Title Page
 Fig. 2
 Table of Contents
 History and background
 Current experiment work
 Components and properties of the...
 Types of degreening rooms
 Construction of degreening...
 Operation of degreening rooms
 Cultural factors affecting...
 Injuries associated with degre...
 Literature cited

Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 620
Title: Degreening of Florida citrus fruits
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00027305/00001
 Material Information
Title: Degreening of Florida citrus fruits
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 80 p. : ill., plans ; 23 cm.
Language: English
Creator: Grierson, William
Newhall, W. F
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1960
Subject: Citrus fruits -- Coloring -- Florida   ( lcsh )
Citrus fruits -- Wounds and injuries -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Bibliography: p. 73-78.
Statement of Responsibility: W. Grierson, and W.F. Newhall.
General Note: Cover title.
General Note: Includes index.
Funding: Bulletin (University of Florida. Agricultural Experiment Station)
 Record Information
Bibliographic ID: UF00027305
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000927058
oclc - 18302504
notis - AEN7761

Table of Contents
    Title Page
        Page 1
        Page 2
    Fig. 2
        Page 3
    Table of Contents
        Page 4
        Page 5
        Page 6
    History and background
        Page 7
    Current experiment work
        Page 7
    Components and properties of the degreening room atmosphere
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
    Types of degreening rooms
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
    Construction of degreening rooms
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
    Operation of degreening rooms
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
    Cultural factors affecting degreening
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
    Injuries associated with degreening
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
    Literature cited
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
Full Text

January 1960

J. R. BECKENBACH, Director
(A Contribution from the Citrus Experiment Station)




Fig. 1.-Degreening cabinets (approximately 50 cubic feet internal capacity
each) used for small-scale experiments.

Bulletin 620


This bulletin is intended as a presentation of what we know
to date concerning degreening of citrus fruits, with particular
reference to Florida conditions.
It is intended primarily for reference and for that reason has
been fully indexed in order that necessary information may be
readily available for readers seeking information on particular
The subject matter has been grouped so as to make available
information on limited aspects (construction, effect of grove
practices, etc.) to building contractors, production managers and
others whose work relates indirectly to the subject of degreen-
ing, but who will not want to read an entire bulletin to obtain
the limited information they need.
Experiments continue here and elsewhere and those not find-
ing the information they need are invited to inquire at the Citrus
Experiment Station, Lake Alfred, Florida. Much of the experi-
mental work reported here has been carried out as a result of
problems brought in by members of the citrus industry.

MMMMM- 1 1 I

Fig. 2.-The modern way: Oranges entering a bulk degreening bin.



INTRODUCTION ---.... ------




Ethylene ..............-......... ---------
Water Vapor ...............................------
Oxygen ................... -.. ---- -
Carbon Dioxide ....--.....- ---------
Organic Volatiles ...............-........- -- -
Nitrogen -......--........- ----------------
Temperature .......-------- --- -----
Air Circulation and Ventilation --------
Slatted-Floor Rooms ....-- ..-- ----------
Solid-Floor Rooms ................-------
Bulk Bins ..........---......- ------ ---.......
Dimensions ..--........ --.-- ---
Exterior Walls .--...... --....----- -- --
Interior W alls .- ..-- .-- ... ..--------------
Doors ...- -- .. ----- --- --------- ------ ----
Floors -----. .. ... --- .... ------ ---- -
OPERATION OF DEGREENING ROOMS ...............-.-- ---
Ethylene ....-.......--......-- --.------
Humidity ...-------- ------------
Temperature ......-......... --- ---
Air Circulation ......------ ---- ----------------
Ventilation .. ----------------
Hardening-off .....---------.--- ------ ---- -

Spray Program --.........-------- -----------
Scale Insects ........--------- ---
Fertilization -........-------- ---------------
Trace Element Nutrition .......----. .. -------
Irrigation ---- ---.. ------ -------- ----- ---------.
Other Factors -------------------------------------
INJURIES ASSOCIATED WITH DEGREENING .-... .---------------------
"Gas Burn" or "Ethylene Burn" of Oranges and Grapefruit
"Gas Burn" or "Ethylene Burn" of Temples ........-----------.-
Handling Damage of Tangerines -----------------------
Peel Injuries of Oranges ....-.....-.-.---------.-----------
Stem-End Rot ..-------------------------------
"Sloughing" of Red Grapefruit .......---------------------
Blue and Green Molds .............----------------
SUMMARY ...------ ------------------------------

INDEX ........----

.-------. 738

- .-.----- -- 8
.........- 13
.----.----- 13
-- 14
.... ... 16

.........-. 18

.. .- 31
....- .. ... 31
S.. 31
...- 32
.. 37
-- 41
--.. 44
.. 47

............. 47
----. 47
.... 49
.. .. 51
.. 52
--. .. 54
... 54

..- .. 56
........ 56
............ 60
..-...- -. 61
... 68
-.. 70
--.-.-. 72
......... 73


Degreening of Florida Citrus Fruits


In many citrus growing districts, Florida being a notable
example, external color and internal quality of the fruit may
bear little relationship to each other. In the absence of cool
nights, early fruits often develop good eating quality while the
external color is still green.
External color of the fruit is due to the presence of the green
pigment chlorophyll and various red and yellow carotenoid pig-
ments. In the absence of chlorophyll, the carotenoid pigments
control external color, which is determined by the total amounts
of yellow and red carotenoids and their relative proportions.
Chlorophyll, if present, can partially or completely obscure
the color due to carotenoid pigments. Even when the fruit is
mature (ripe), various factors may cause chlorophyll to persist
or to reappear in the peel of citrus fruits. Warm weather (par-
ticularly warm nights), high rainfall, high nutrient levels or
any other conditions tending toward vigorous growth tend to
cause chlorophyll to persist or reappear.
In Florida this discrepancy between exterior color and in-
ternal quality can be a considerable obstacle in marketing such
early varieties as Hamlin and Parson Brown and late varieties
such as Valencia and allied strains such as Lue Gim Gong and
Pope Summer.
When buying oranges, grapefruit or tangerines the public
inevitably associates green color with immaturity. Hence pack-
inghouse operators choose to remove this green color by degreen-
ing with ethylene gas, thus destroying the chlorophyll in the
peel without having any "ripening" effect upon the internal tis-
sues. Ethylene degreening of citrus is therefore very different
from ripening of starchy fruits such as bananas, pears or imma-
ture apples. Such ethylene treatment of citrus is variously
known as "coloring," "sweating" or "degreening," according to
the parlance of the citrus growing district concerned. Although
"coloring" is quite commonly used in Florida, "degreening" is
quite the most accurate and specific term and is favored by other
research agencies such as the USDA (67, 95, 98, 100). Hence
it is used throughout this bulletin. It is important to distin-
1Associate Chemist and Assistant Biochemist, respectively, Citrus Ex-
periment Station, Lake Alfred.

Florida Agricultural Experiment Stations

guish between degreening and the "color-added" process by
means of which red or orange color is added to the fruit by
the use of a dye emulsion.
If correctly carried out, degreening does not harm the inter-
nal quality of the fruit which in Florida has to meet exacting
legal standards (17, 59). Susceptibility to certain forms of de-
cay is increased by degreening (7, 24, 35). Early in the season
the output of Florida packinghouses is limited by 2 principal
The first is the quantity of fruit that can pass the legal stand-
ards for maturity. Such standards include an initial "color
break" that must be caused solely by nature, but it can usually
be assumed that any fruits that pass the requirements for juice
content, soluble solids and ratio of soluble solids to acid will be
considered acceptable for degreening. "Spot picking" is often
employed to harvest the very early fruit and Sites and Reitz
(74) have published a detailed study of factors that can help in
such spot picking for internal quality.
The second principal factor limiting output is the amount of
fruit that can be put through the degreening rooms. The rate
at which fruit can be put through the degreening rooms de-
pends on the capacity of the degreening rooms and the time
required to degree. Since time to degree fruit in an ineffi-
cient degreening room may easily be twice that taken in an effi-
cient set-up, it is apparent that the efficiency of degreening prac-
tices materially affects the early season capacity of Florida pack-
inghouses. The importance of this is emphasized by the fact
that, particularly in houses packing a high proportion of grape-
fruit, the season's profits are determined very largely by the
volume of fruit shipped early in the season when prices are high.
This volume depends on the amount of fruit handled through
the degreening rooms and the proportion of this fruit that can
be packed ("percent pack-out"). Profits react very sharply to
this factor of pack-out due to the fact that, particularly early
in the season, packinghouse eliminations may have to be dis-
posed of at a loss (20, 21). Moreover, persistent green color is
an important factor in determining grade (91, 92, 93), and in
some seasons green color accounts for the rejection of more fruit
than any other grade factor (19).
Thus, efficiency of the degreening operation can have a major
effect upon the profits in handling Florida citrus, particularly
early in the shipping season.

Degreening of Florida Citrus Fruits

The history of degreening is very much involved with the
process variously known as "curing," "sweating" or quailingg."
In the 1870's E. Bean, pioneer Florida shipper, advocated
holding fruit for several days until it was slightly wilted, or to
use his own phraseology (as quoted by Hume (43)), "until the
skin was softer and more pliable." In some countries this is still
the normal practice, even when no degreening is carried out, e.g.,
in Australia (42) and the West Indies (94). In districts where
the Mediterranean fruit fly is endemic, such a curing period is
commonly used to hasten the breakdown of infected fruit so
they can be graded out. Hopkins and Loucks (36) have advo-
cated "curing" of Florida citrus to reduce losses from blue and
green molds.
Since the original purpose of this "curing" was to reduce
mechanical damage by increasing the pliability of the rind, it
became customary to use kerosene stoves to raise the tempera-
ture and hence hasten wilting. It was noted that this also
hastened the disappearance of green color, but this was th-n
believed to be due to the increase in temperature. In 1912 Sie-
vers and True (70) reported that such degreening was not due
to heat, but due to some unidentified product of the incomplete
combustion of kerosene.
In 1923 Denny (12, 13, 14) showed that the active constitu-
ent was ethylene. No really major advance has been made since
Denny's day. In fact, kerosene is still used to a surprising ex-
tent. Some excellent and progressive packinghouses claim they
get better color than when using pure ethylene, particularly with
tangerines. Such advances as have been made recently are
either in doing a better job of air conditioning (degreening tech-
niques are essentially a matter of air conditioning the individual
fruit) or else in more efficient handling methods.

The Citrus Experiment Station, Lake Alfred, conducts a con-
tinuing program of research on packinghouse methods, includ-
ing degreening. Wherever possible, experimental results are
quoted throughout this bulletin to illustrate points under discus-
sion. If such results have been published, the prior source of
publication is acknowledged. Results that do not carry acknowl-

Degreening of Florida Citrus Fruits

The history of degreening is very much involved with the
process variously known as "curing," "sweating" or quailingg."
In the 1870's E. Bean, pioneer Florida shipper, advocated
holding fruit for several days until it was slightly wilted, or to
use his own phraseology (as quoted by Hume (43)), "until the
skin was softer and more pliable." In some countries this is still
the normal practice, even when no degreening is carried out, e.g.,
in Australia (42) and the West Indies (94). In districts where
the Mediterranean fruit fly is endemic, such a curing period is
commonly used to hasten the breakdown of infected fruit so
they can be graded out. Hopkins and Loucks (36) have advo-
cated "curing" of Florida citrus to reduce losses from blue and
green molds.
Since the original purpose of this "curing" was to reduce
mechanical damage by increasing the pliability of the rind, it
became customary to use kerosene stoves to raise the tempera-
ture and hence hasten wilting. It was noted that this also
hastened the disappearance of green color, but this was th-n
believed to be due to the increase in temperature. In 1912 Sie-
vers and True (70) reported that such degreening was not due
to heat, but due to some unidentified product of the incomplete
combustion of kerosene.
In 1923 Denny (12, 13, 14) showed that the active constitu-
ent was ethylene. No really major advance has been made since
Denny's day. In fact, kerosene is still used to a surprising ex-
tent. Some excellent and progressive packinghouses claim they
get better color than when using pure ethylene, particularly with
tangerines. Such advances as have been made recently are
either in doing a better job of air conditioning (degreening tech-
niques are essentially a matter of air conditioning the individual
fruit) or else in more efficient handling methods.

The Citrus Experiment Station, Lake Alfred, conducts a con-
tinuing program of research on packinghouse methods, includ-
ing degreening. Wherever possible, experimental results are
quoted throughout this bulletin to illustrate points under discus-
sion. If such results have been published, the prior source of
publication is acknowledged. Results that do not carry acknowl-

Florida Agricultural Experiment Stations

edgment of prior publication refer to hitherto unpublished find-
ings from this Station.
Many of these experiments deal with the effect of various
factors on the length of the degreening period expressed as an
exact number of hours. This value is arrived at by the following
method. Samples under treatment are removed from the de-
greening rooms and examined daily in a colorimeter essentially
similar to that described by Baier and Ramsey (1, 68). At least
3 readings, and sometimes as many as 12, are taken on each
sample and averaged. These averages are then plotted against
time and, from the curve thus obtained, the time to reach an
arbitrarily selected color is taken as the time to degree. These
arbitrarily selected colors have the following notations on the
Munsell (52) scale: oranges Y 8/8; tangerines YR 6/10; grape-
fruit gY 8/12. When repeating experiments over a considerable
period, comparison of results is complicated by the fact that
both degreening time and the amount of subsequent decay
change considerably with the advancing season. Hence, in some
experiments degreening time and decay are compared in terms of
percent, with the results for a control sample degreened under
standard conditions (85' F. dry bulb, 820 F. wet bulb and a con-
stant ventilation rate determined by using a 3/64-inch ventilator
setting on a 4-foot x 4-foot x 4-foot degreening cabinet such as
is shown in Figure 1.
Statistical evaluation of data has been made by the methods
of Snedecor (76).

Ethylene.-Ethylene is a gas at all temperatures above
-103.90 C. It is the simplest of the chemical compounds known
as unsaturated hydrocarbons, having the chemical formula of
CH2=CH2. It occurs in minute quantities in the organic vola-
tiles given off by most fruits. Commercially it is manufactured
as a by-product of the petroleum industry. As mentioned ear-
lier, its role in the degreening of citrus fruits was discovered in
1923 by Denny (12, 13, 14), who was investigating the degreen-
ing of citrus fruits by means of kerosene fumes.
Several other unsaturated gaseous hydrocarbons also act as
degreening agents, although none is as effective as ethylene.
Because it can be made so easily (by adding water to calcium
carbide), acetylene is used in some parts of the world (45, 79),

Degreening of Florida Citrus Fruits

despite the higher concentrations necessary and the greater dan-
ger of explosion.
Ethylene exerts its physiological effects at extremely low con-
centrations. Concentrations as low as 1 part in 20 million
(0.000,005 percent) will damage small seedling plants (15, 65).
Higher concentrations are used in degreening citrus, recommen-
dations ranging from 1:50,000 (1, 97) to 1:5,000 (18, 29, 56)
or even as high as 1:1,000 in 1 instance (79). Once degreening
action is initiated, increasing the concentration of ethylene does
not speed up degreening and may cause damage to the fruit (18,
24, 97).
Unfortunately there is no rapid analytical method for ethy-
lene suitable for use by the packinghouse operator. Hence de-
greening room conditions have to be set up so as to arrive at the
desired ethylene concentration by "rule of thumb." As a conse-
quence of this, it is very common for ethylene concentrations to
be excessively high. In districts where stem-end rot due to
Diplodia 2 is common, excessive amounts of ethylene greatly
increase losses from stem-end rot (4, 6, 7, 18, 24, 44, 97). This
is apparent from the results in Table 1, which shows the effect
upon subsequent decay of various rates of ethylene delivery. In
these experiments 40 cc. per hour was barely adequate for de-
greening and 80 cc. per hour was sufficient to give the fastest
possible degreening. Hence ethylene at 120 cc. per hour ap-
proached twice the minimum concentration necessary for de-
Ethylene is explosive in concentrations between 3 percent and
34 percent in air (51). This should never need to be a hazard
in the packinghouse, since the range of concentrations used for
degreening lies between 0.02 percent and 0.002 percent (1:50,000
to 1:5,000). However, it is not safe to seek ethylene leaks with
a lighted flame, and reasonable precautions should be taken
when administering a single initial charge of ethylene instead
of using the trickle system. When several cubic feet of gas are
admitted into a confined space, the atmosphere in the immediate
vicinity momentarily passes through the range of explosive con-

SIn Florida stem-end rot is caused by either of two organisms: Phomop-
sis citri Faw. (which is also the causal organism of melanose) and Diplodia
natalensis Evans (which is also the causal organism of bark and wood dis-
eases such as collar rot, root rot, twig and branch die-back). Both of these
organisms are endemic in Florida groves. Diplodia, but not Phomopsis, is
stimulated by ethylene (6, 7, 47).

Florida Agricultural Experiment Stations

HALL (24).

Type of No. of
Fruit Expts.

Oranges ............ 2
Oranges ....-....... 3
Oranges ...........-- 5
Tangerines ..... 4
Grapefruit ...... 4
Foster Pink
Grapefruit ...... 1

No. of






Percent Average Total Wast-
age at 3 Weeks from Picking

I Ethylene as cc./hr.
0 40 80 120

26.0 27.6 33.7 36.0

S13.2 22.2 26.2 29.2

30.1 59.4 67.6 76.1
44.2 47.4 60.4 56.1

4.6 15.7 22.7 27.5

1.7 8.3 5.0 10.0

Too few experiments for statistical evaluation.
** Significant at the 1 percent level.
t Significant at the 5 percent level.
("Significant at the 5 percent level" means that the odds are at least 19:1 that these
differences are real. "Significant at the 1 percent level" means that the odds are at least
99:1 that these differences are real.)

Under degreening room conditions, i.e., with very low concen-
trations of ethylene in the atmosphere and a temperature of ap-
proximately 850 F., ethylene has very low solubility in water.
This becomes of some significance in understanding the behavior
of wet fruit in the degreening process.
Just how ethylene destroys the green coloring matter in the
rinds of citrus is still not known. Nor, for that matter, are the
many other roles played by ethylene in plant physiology under-
Water Vapor.-Water vapor is another essential constituent
of the degreening room atmosphere. The fruit is constantly
giving off water vapor. If this process is not checked, the fruit
rapidly shrivels and becomes unsaleable. The rate of loss of
water vapor from fruit varies inversely with the relative hu-
midity of the degreening room atmosphere. Hence the higher
the humidity, the less the shrivelling that will result. At 100
percent relative humidity shrivelling ceases, but condensation
starts, and wet fruit is associated with a number of degreening
room troubles. A film of water on the fruit tends to slow up


Degreening of Florida Citrus Fruits

degreening, an effect that appears more consistently with grape-
fruit than with oranges.
Table 2 shows results of a number of degreening experiments
using 3 different humidity levels. As has been noted before
(23), the rate of degreening of oranges did not appear to be con-
sistently affected by humidity levels. This is interesting in view
of a California report (1) that their oranges fail to degree
properly at very low humidities. A more significant result of
low humidity is the consequent softening of the fruit, as lack
of firmness is a grade lowering factor (92). Rate of degreening
of Duncan grapefruit was consistently and significantly slowed
by excessive humidity. That wet fruit can be hard to degree
is a common observation in Florida and elsewhere (79).


Time to Degreen (Control = 100)
Fruit Picking Date RRelative Humidity
Low Normal High
(65-75% i (80-90% i (90-100%
R.H.) R.H.) R.H.)
Hamlin Sept. 26, 1952 97 100 100
Oct. 1, 1952 100 100 105
Oct. 6, 1952 104 100 103
Sept. 28, 1953 94 100 114
Oct. 14, 1953 110 100 110
Oct. 19, 1953 113 100 93

I Averages 103 100 106

Differences not significant

Duncan Sept. 28, 1953 98 100 124
Oct. 14, 1953 100 100 112
Oct. 19, 1953 96 100 128

Averages 98 100 121.3
L.S.D. (5% level)** 12.3
Time is expressed as relative to the time taken to degree a control sample at normal
** "L.S.D." means "least significant difference" and refers to the difference necessary
before the odds are 19:1 (5 percent level) or 99:1 (1 percent level) that such differences
between treatments are real.

Florida Agricultural Experiment Stations

Another trouble that is aggravated by moisture condensation
is loss due to fungi (rots). Fungal losses, particularly stem-
end rot, can be greatly increased by humidities high enough to
cause occasional condensation. This is illustrated in Table 3,
which shows the effect upon subsequent decay of various levels
of relative humidity during the degreening period. It is ap-
parent from the results shown here that excessive humidity has
a much more consistent effect upon subsequent rots than it does
on rate of degreening. Attention is drawn to the complex rela-
tionships between humidity, peel injury and decay as discussed
in the section on "Injuries associated with degreening".


Percent Total Losses at 3 Weeks
Picking from Picking
Fruit (1953) D Relative Humidity
Low Medium High
(65-75% (80-90% (90-100%
R. H.) R. H.) R. H.)

Hamlin Sept. 28 22.0 48.7 42.0
Oct. 14 18.7 18.0 34.7
Oct. 19 50.0 48.7 44.0

Averages 30.2* 38.5* 40.2*

Duncan Sept. 28 5.3 10.7 30.7
Oct. 14 17.3 30.7 48.0
Oct. 19 20.0 22.7 34.7

Averages 14.2 21.4 37.8

L.S.D.** (5% level) 7.63
(1% level) 11.96

Differences not significant.
** See explanatory note, Table 2.

Another harmful effect of such condensation is sometimes
encountered. A peculiar ring-like injury sometimes occurs at
the points of contact between wet fruit (Figure 22). This is
popularly attributed to ethylene dissolved in the surface water,
but it is almost certainly attributable to dirt, spray residues,

Degreening of Florida Citrus Fruits

etc., dissolved in the water that gathers at these points. As
the water evaporates, the solution ultimately can become strong
enough to cause tissue injury. This action is essentially the
same as "fertilizer burn" on plants.
From the foregoing it will be seen that humidity levels high
enough to cause condensation during degreening are associated
with slow degreening, increased decay and other troubles. On
the other hand, low humidities, while checking decay, cause ex-
cessive shrinkage, shrivelling, what Rose et al. have termed
"stem-end aging" (66) and other forms of peel breakdown often
followed by increased decay (41). Thus, the humidity should
be maintained as high as possible without causing condensation
and its consequent problems.
Oxygen.-Since living fruit respire continually (i.e., take in
oxygen and give off carbon dioxide and heat), they must have
adequate oxygen if they are not to develop serious off-flavors.
Also, it has been demonstrated (14, 48) that oxygen is necessary
for the degreening action of ethylene to take place. Because
of this, it is sometimes stated that oxygen levels can fall low
enough in the degreening room to slow up degreening. This is
most unlikely to happen, as quite elaborate measures have to be
taken when lowering oxygen levels intentionally as in controlled
atmosphere storage.
Carbon Dioxide.-For every volume of oxygen used by the
fruit in respiration, 1 volume of carbon dioxide (COs) is given
off. Carbon dioxide is an excellent plant narcotic and is used to
arrest ripening and color change in such fruits as apples and
pears and in stored cut flowers. Its action is just as marked
with citrus fruits. It has been found in South Africa (56), Cali-
fornia (1) and Florida (18) that as little as 1 percent of carbon
dioxide almost completely arrests degreening, even in the pres-
ence of what would otherwise be an adequate concentration of
In view of this, it becomes imperative that carbon dioxide
levels be kept down during degreening. Since the fruit produces
carbon dioxide continually, this can be accomplished econom-
ically only by some form of ventilation.
Organic Volatiles.-In addition to giving off carbon dioxide
and water vapor, fruits of any kind also give off minute quanti-
ties of organic volatiles. Ethylene is 1 of these. But other vola-
tile compounds also are given off, some of which account for the

Florida Agricultural Experiment Stations

distinctive aroma of each kind of fruit. As well as the volatiles
evolved by respiratory processes, citrus fruits give off appreci-
able quantities of peel oil whenever the oil glands in the rind
are damaged. The effect of such volatiles on degreening is not
known, but it has been shown (36) that peel oil atomized directly
onto the fruit materially increases losses from decay. Also,
peel oil destroys epidermal cells, causing "oil spotting" or oleocel-
losis. Experiments in which peel oil has been volatilized in the
degreening chamber have not shown enough consistent increase
in decay to justify attributing decay due to poor ventilation to
such volatiles alone. Measures to keep down carbon dioxide in
the degreening rooms will also tend to reduce the level of organic
volatiles and so may serve a twofold purpose.
Nitrogen.-Seventy-five percent or more of the degreening
room atmosphere is made up of nitrogen. Gaseous nitrogen is,
however, completely inert and plays no part in the degreening
Temperature.-Temperature is of crucial importance in the
degreening of citrus fruits, affecting the process in many ways.
Chemical reactions are certainly involved in the destruction of
chlorophyll, and in general the speed of chemical reactions in-
creases with increasing temperature. Within plant tissues, how-
ever, a limit is soon reached as chemical reactions are controlled
by enzymes, which are sensitive to temperature.
In addition to such chemical effects, the temperature acts
through such physical means as affecting diffusion rate of gases,
the relative humidity resulting from a given amount of water
vapor in the air, etc. Nor are the effects of temperature limited
to those exerted directly on the fruit. The severity of injury
by various fungi causing such diseases as blue mold and stem-
end rot is also directly related to temperature.
The interplay of all these factors results in an optimum tem-
perature above or below which degreening is slowed down. This
optimum tends to vary with variety, season and, most strikingly,
with the particular citrus growing area. For Florida citrus it
has been found to lie in the neighborhood of 850 F. (10, 18, 23,
25). This is considerably higher than is generally the case in
other citrus growing areas throughout the world (67, 79). In
experiments at the Citrus Experiment Station, Lake Alfred, it
has been found that, in general, raising the temperature above
850 F. slows up degreening at least as much as does an equivalent

Degreening of Florida Citrus Fruits

decrease in temperature below 85' F. This is apparent in the
results shown in Figure 3.

WJ >.
w .
0a 140-
W z

s w

Z 0
o i
z z

Fg1 -fe


Fig. 3.-Effect

70* 75* 80* 85* 90* 95* 100"
of temperature on rate of degreening of Hamlin oranges.
Adapted from Grierson and Newhall (23).

In Florida the maximum degreening temperature when heat
is being applied is set by law at 850 F. (59). The wisdom of this
ruling is shown by the data in Table 4 and Figure 3. In the ex-
periments reported in Table 4 there is a tendency for subsequent
decay to increase with increasing temperature, the effect being

Florida Agricultural Experiment Stations

more marked with Marsh and Duncan grapefruit than with Ham-
lin oranges. In commercial practice these differences could be
expected to be greater since, as is shown in Figure 3, degreening
period increases with increasing temperature above 850 F.
Hence, to achieve a comparable degree of color, fruit degreened
at higher temperatures would have to be left in the room longer
and a consequent further increase in decay could be expected.
Attention is also drawn to Table 12, which shows the role of
temperature as affecting so-called "gas-burn."

TURES FROM 800 TO 91' F.

Variety No. of

Hamlin .... 3
Marsh .... 4

Hamlin .... 7
Duncan -... 4

Average Percent Total Decay at
3 Weeks from Picking Date
I: Degreening Temperatures
50 80' 850 90

7.6 27.4 28.4 30.3
3.4 21.6 23.6 27.0

II: Degreening Temperatures
3 850 88' 91

0.8 22.0 24.1 23.2
0.0 16.6 16.3 18.7

See explanatory note Table 1.
** Significant at the 5 percent level.
t Not significant.

In citrus degreening the temperature of the rind is the only
temperature exerting an effect. It is not uncommon to find
operators running temperatures as high as 1000 F. soon after
closing the rooms "in order to get the pulp temperature up."
Such a practice is not only useless, it is definitely harmful.
Air Circulation and Ventilation.-Air circulation within the
rooms serves 2 principal purposes. The first is to equalize con-
ditions throughout the room. The best indication in this regard
is temperature. If the temperature is kept constant throughout
the degreening rooms, it is certain that air circulation is suffi-
cient to ensure an equitable distribution of ethylene in the at-



Degreening of Florida Citrus Fruits

Related to the matter of air circulation, but nevertheless sep-
arate, is the controversial subject of ventilation. More differ-
ences of opinion exist with regard to ventilation methods than
all the other aspects of degreening combined. Much of this is
due to lack of comprehension as to just what ventilation seeks
to accomplish. It is often said that the principal functions of
ventilation are to introduce fresh air or oxygen and to lower the
temperature. If either of these is needed, it is because condi-
tions in the degreening room were faulty in the first place.
The function of ventilation is to remove the waste gases
(carbon dioxide, volatiles such as peel oil vapor, etc., and possibly
excess water vapor) before these can slow up degreening or stim-
ulate decay. If this is done well enough to maintain optimum
degreening, then there will always be enough fresh air or oxygen.
The apparent advantages occurring from cooling during inter-
mittent ventilation are probably due to the excellent air circula-
tion when cold air is blown over stacks of warm fruit, an effect
that is particularly marked in cold weather or when degreening
temperature has been too high.


No. of ITime to Degreen* Decay**
Type of Ventilation Experi- I
ments Hamlin Duncan Hamlin I Duncan

Nonet ............................ 5 99 110 35 22
(three times daily) 8 99 99 40 31
Continuous: 1/64" ......... 1 108 88 47 42
Continuous: 3/64" ....... 6 100 100 29 26
Continuous: 1/16" ....... 119 109 25 6

Time to degree is expressed as a percentage of the time taken to degree a control
** Decay is expressed as average percent unmarketable fruit at three weeks from picking.
t Ventilation was actually more than "none" since samples had to be removed daily for
color readings.
Control sample was that using continuous ventilation at 3/64 of an inch. This refers
to the setting on the ventilators of the experimental cabinets shown in Fig. 1.

Experiments at the Citrus Experiment Station have indicated
that, providing carbon dioxide is kept well below 1 percent, the
particular method of ventilation does not have any very con-

Florida Agricultural Experiment Stations

sistent effect upon rate of coloring. An effect has been noted,
however, on subsequent decay and is apparent in the results
shown in Table 5. Possibly the increase in decay due to periodic
ventilation as compared with no ventilation was due to condensa-
tion of moisture caused by the unavoidable temperature fluctu-
ations during ventilation periods. Decay in samples subjected
to various rates of continuous ventilation tends to decrease as
ventilation increases. However, a practical limit is set on the
amount of ventilation due to loss of ethylene. It will be noted
that at the maximum rate of continuous ventilation degreening
time was increased by up to 19 percent.

Many different types of degreening rooms exist, but they
can be broadly classified according to: (1) whether air delivery
is up from the floor or down from the ceiling; (2) whether solid
or slatted floors are used. A further type is the bulk degreening
bin in which boxes are not used. Instead, the fruit is harvested
in bulk, using special equipment to minimize damage. On ar-
rival at the packinghouse it enters the top of tall degreening
bins (see Figure 2). In these bins the fruit rest on baffles of
soft porous cloth while being degreened. This method is de-
scribed in detail elsewhere (55, 57) and hence will be mentioned
only briefly here.
Slatted-Floor Rooms.-Slatted-floor rooms are of 2 principal
types which are usually known in Florida by the names of the
companies that install them. The older type (Hale rooms, see
Figures 4 and 5) have overhead fans that deliver air downward
in the center of the room. The fan is above the ceiling and
draws air from beneath the slatted floor through a shaft at the
side of the degreening room. The space under the slatted floor
is limited to the depth of the joists (about 8 inches), the joists
being arranged radially, converging at the air return shaft. The
theory behind this is that the space between the joists is sup-
posed to act as return air ducts drawing air from under the
whole room. This is fallacious, as the spaces between joists are
tapered in the wrong direction for action as return ducts, and
in practice the authors have found that nearly all the air being
returned to the fan is drawn from the immediate vicinity of the
return shaft. Hence air distribution in this type of room depends
principally on the air from the ceiling delivery spreading over

Degreening of Florida Citrus Fruits

the surface of the fruit. Thus, it is advantageous to have the
fruit stacked tightly to spread the incoming air over the surface
of the entire load of fruit, letting it move down through the
stacked fruit more due to pressure build-up than to direct blast
from the fan. Small Hale-type rooms (e.g. 400 boxes) can be
quite efficient. With larger rooms of this type (e.g. 1,200 boxes)
real inefficiency occurs, due to the fact that the bulk of the air
tends to move along the shortest possible path from the air de-
livery to the return duct, thus by-passing most of the fruit in
the room.
Centrifugal Fan
Adjustable Air intake Motor Ethylene Line
efor Ventilation) /
earn Radiator
Steam' Line
iter Spray

Perforated /
SBaffle /
I From Ethylene Tank

Heavy Doors
r Return Duct

dating Joists

Fig. 4.-Diagrammatic representation of a Hale-type degreening room.
(Note that the scale is distorted, the size of the room being small by con-
trast with that of the machinery.) Compare with Figure 5.

A more modern type of slatted-floor room is the type that
Florida operators usually refer to as F.M.C. rooms (Figures 6
and 7). In this type of room the fan and air conditioning appa-
ratus are below floor level. The space under the floor is usually 2
to 3 feet deep. A portable metal duct or "stack" is placed over
the fan and directs the air blast against a conical deflector at
ceiling level. Thus the action of the fan causes a vacuum (low
pressure) area below the floor and a plenum (high pressure)
area above the fruit, thereby inducing a steady air movement
downward through the fruit.

20 Florida Agricultural Experiment Stations


*fL~~: *,".-.
r~_l;-- ..r:";~rL~E~'~:;~

, i

f :I Ij*A

Fig. 5.-Above, machinery and below, interior of a typical Hale-type room.
(Compare with diagrammatic view in Figure 4.)

: 4

Conical Baffle or "Diverter"

Ceiling /

Wall / High Pressure (Plenum)Areo High Pressure (Plenum)Areo
or r
Curtain Cr"

I 1 i I/i 1 \ It 1 11_ ___
B I-- %Z Ie

Portable Stock
Ethylen Supply Water Supply
thyln Supply Steam Nozzles /
Slotted Floor Fan Finned Radiator "
Joist /
Partition oo.....r / Adjustable Fresh
Low Prssue )Va Ic .. uu...) Area Air Inler--_ .V
Fig. 6.-Slatted-floor degreening room. Note that the use of a slatted floor with an air space below allows for
the establishment of a low pressure area under the stacks of fruit and a high pressure above, with a consequent
flow of air downward through the stack. Note also that the presence of the vacuum area under the floor allows con-
tinuous ventilation by means of an adjustable opening. (Compare with Figure 7.)

Fig. 7.-Interior of a small FMC-type degreening room, above. View
of the fan, steam and water nozzles (below) visible below floor level when
the stack is removed. The steam radiator is below the fan. (Compare with
Figures 6 and 13.)

Degreening of Florida Citrus Fruits

In small rooms (e.g. 400 boxes) a very even air distribution
results. In larger rooms (e.g. 1,200 boxes) there is marked
tendency for air movement to be excessive in the region of the
stack and insufficient through the stacks of fruit remote from
the fan. For this reason, in this type of room, the fruit should
be stacked tightly, especially in the center of the room. It should
not be stacked tightly against the walls, lest the air currents
from the fan be deflected back toward the center of the room.
This is easily demonstrated with a smoke generator such as a
bee smoker.
A better device is the 1 used at Lake Alfred, a titanium tera-
chloride smoke gun that generates a "cold smoke." Figure 6
shows the movement of air in this type of room.
Occasionally trouble is encountered when a single unit of this
type is used in a long narrow room. Since there is very little
momentum to force air toward the ends of the room, consider-
able inequalities in air circulation can result. Figure 8 shows 1
way of dealing with this. The simple ceiling ducts constructed
of wallboard deliver air to the ends of the room.
Solid-Floor Rooms.-When solid floors are used, it is no longer
possible to establish a pressure differential between the areas
above and below the fruit. Hence a pressure differential has to
be established on either side of the stacked fruit. Figure 9
shows how this is accomplished when a generous space is left
around the walls. Air moves across the ceiling and down the
walls, forming a plenum high pressure area. The fan in the
central stack is drawing air from the center of the room at floor
In this type of room it is clearly advantageous to have the
fruit stacked with spaces between the rows and, if possible, be-
tween the stacks. The air can then move back to the fan in the
manner indicated in Figure 9. The space at the walls contributes
greatly to the efficiency of this type of room. Such a space can
easily be ensured by running a rail around the room about 6 or 8
inches from the wall. It is better still to use a double rail, 1
about the height of the second box and another at the height of
the fourth box. This saves close supervision of truckers load-
ing the rooms.
No matter how excellent the reasons for not doing so, there
is an inevitable tendency to overload degreening rooms and the
effect of this is particularly bad in solid-floor rooms. Another
disadvantage of most solid floor rooms is that the permanent

Florida Agricultural Experiment Stations




Degreening of Florida Citrus Fruits

center stack in the middle of the room complicates the loading
and unloading of the room, particularly when using power trucks.

High Pressure Area

0L[IItI i I

:IIIiIiii -: ,


High Pressure Area
PLAN Cailina
High Pressure Arro a

F 1-1-

--Is w -w --- .. ]

-74 Low Pr ,ssure eArea *- |
<^^^^^^/// /////-///.//,//Solid Floor//', ./'////// /////
Fig. 9.-A typical solid-floor degreening room using a fixed center stack.
Note how efficient air distribution depends upon leaving an adequate air
space at the walls. (Compare with Figures 10 and 14.)

The authors have designed a new type of solid floor room in
which overloading is of less consequence and in which the center
stack is completely mobile and can be pushed into place as load-
ing of the room progresses (Figure 10). Equally suitable is a
stack with an angle iron base moved by clamp trucks. In this
type of room the fan, steam heat and ethylene are all in a unit

Fig. 8.-Above: Use of simple ceiling duct to distribute air to the ends
of a degreening room. Vertical 2 x 6's prevent stacking against the end
walls and allow channels for good air distribution. Below: Duct encloses
standard conical baffle. The space between the stack and the duct prevents
backpressure developing against the fan and allows air delivery to the cen-
ter of the room. The dark object in the upper right corner is the tempera-
ture-sensitive element of the automatic control on the steam line.

Fig. 10.-A new design for solid-floor degreening rooms. Note that all services are in the ceiling and hence the
stack can be very light and portable; air is delivered into the middle of the stacked fruit; the double ceiling prevents
"short circuiting" back to the fan. The thermostat is in the airstream under the fan. (Compare with Figure 9.)

Degreening of Florida Citrus Fruits

in the ceiling. The fan blows downward into a portable stack
with a cross-section identical with that of 2 stacks of fruit and
hence fits into the loading pattern. The bottom part of the stack
is open and thus the conditioned air is forced into the center of
the stacked fruit. The room has a false ceiling with a narrow
opening at ceiling level around the perimeter of the room; the
effect of this is to force the air to pass through the stacks of
fruit prior to returning to the fan. If a steam jet is to be used,
it should open above the radiator and into a container with a per-
forated top to catch any drops of hot water. If automatic venti-
lation is desired, it can be provided by running an open pipe from
the outside, above the false ceiling to the vacuum area immedi-
ately above the fan. The end outside the room is then equipped
with an adjustable damper. A number of these rooms have
been built and are performing very satisfactorily. One warning
is necessary, however. Since the air passes through the fruit
prior to reaching a thermometer placed in any easily accessible
position, the air temperature is being checked at a point at which
heat has been given up to the fruit and the air is returning to
the unit for re-heating. Therefore, such rooms must be run
with the apparent temperature reading about 3 degrees lower
than is customary. A dry bulb temperature of 850 F. should
be considered the absolute maximum and the sensitive unit of
the thermostat should be under the fan.
This type of room is excellently suited to degreening citrus in
large "pallet boxes" (101).
Many solid-floor rooms exist that do not correspond to any
of the types described above. In very small rooms faults in cir-
culation patterns seldom cause apparent harm. In larger rooms
some of these improvised systems can prove very inefficient un-
less modified to give desirable air circulation patterns.
To summarize: either slatted-floor or solid-floor rooms can
be very efficient, provided an intelligent effort is made to see
that all fruit is situated between areas of high and low pressure
with consequent systematic air movement. Slatted-floor rooms
are more foolproof and usually easier to run. Solid-floor rooms
need more care in stacking, but are easier to keep clean and ad-
mirably suited for power trucks. An improved design is offered
for solid-floor rooms.
Bulk Bins.-The concept of degreening fruit in bulk is not
new, but only within the past few years has it been practiced
successfully. Bulk degreening is a necessary part of any bulk

Florida Agricultural Experiment Stations

harvesting and handling operation that eliminates the use of
field boxes. As a result of designs developed by the Citrus Ex-
periment Station and the operational data obtained in coopera-
tion with several commercial packinghouses3, bulk degreening
has now become an accepted practice in Florida. The construc-
tion of bulk degreening bins is described elsewhere (55, 57) and
plans are available from the Citrus Experiment Station. A typi-
cal design is shown in Figures 11 and 12. Attention is also drawn
to Figures 2 and 19.

Stp -I 5

Ia'. CW ,- .. .'-0

Fig. 11.-Cross-section through a typical bulk degreening bin. The cloth
baffles are secured by wooden members which are shown. The cloth baffles
are not shown, but are clearly visible in Figure 12.

3 Acknowledgment is made to Haines City Citrus Growers Association,
Chase and Company, and the Indian River Exchange Packers for their co-
operation in experiments on bulk degreening.


Degreening of Florida Citrus Fruits


Fig. 12.-Interior of a bulk degreening bin in the process of being loaded.
The lowest visible baffle is full and the fruit is starting to build up on the
next baffle. The cloth used is soft and porous, allowing adequate air move-
ment through the fruit. (See also Figure 11.)


-- -

*i *

Florida Agricultural Experiment Stations

The introduction of bulk degreening has introduced a number
of new possibilities, since the fruit can be given various pretreat-
ments such as washing, pregrading, treatment with fungicides,
etc., prior to degreening. This, in turn, has given rise to a num-
ber of new problems, outstanding among which is the matter of
whether fruit should be washed prior to degreening.
The arguments in favor of washing prior to degreening are
that (1) the bins remain much cleaner; (2) pregrading is facili-
tated; (3) when degreening capacity limits the amount of fruit
handled, then such pregrading increases the total output of the
The principal argument against washing prior to degreening
is that washing slows up the degreening process. When the
degreening period is down to 36 hours or less, it seems likely that
the advantages of washing ahead of degreening outweigh the
disadvantages. For very early fruit, particularly grapefruit,
the slowing of degreening due to washing can be very serious.
Table 6 shows the results of a series of experiments comparing
the degreening of washed and unwashed early Duncan grape-
fruit and Hamlin oranges. In another series of experiments
prior washing slowed up degreening in 39 of 44 trials using 4
varieties of grapefruit and 2 of oranges. The average percent
increases in degreening time were: Duncan 42, Marsh 23, Ruby
Red 31, Foster Pink 28, Hamlin 13 and Parson Brown 17 (27).
Why washing slows degreening is not known, but it is associated
in some way with brushing. Merely dipping the fruit in water
has no consistent effect upon degreening. Passage over the
washer brushes (either with or without soap) causes an appre-
ciable slowing of degreening. If grapefruit are then dried on a
polisher-drier4, a drastic increase in degreening time usually
results (Table 6).
The Florida packinghouse that first adopted bulk handling
combined it very successfully with pre-washing and use of the
Dowicide A-hexamine fungicidal treatment (37, 38), which also
causes some delay in degreening of very early fruit. This pack-
inghouse, however, is 1 that makes a principle of not picking
until the natural color break is well advanced.
Waxing has an even more drastic effect in stopping degreen-
ing. Despite the fact that this was reported by Winston and
Lutz as long ago as 1931 (95), there are still occasional attempts
SThe term "polisher-drier" refers to a drier in which hot air is blown
over the fruit as it passes over transverse horsehair, or fine nylon, brushes.

Degreening of Florida Citrus Fruits

to degree waxed fruit that has been graded out as being too
green. This practice is never successful.


Fruit Picking Date Time to Degreen in Hours Washed
Unwashed Dipped Washed Polished

Duncan Sept. 24, 1954 63 63 90 120
Sept. 28, 1954 61 48 73 92
S Oct. 12, 1954 64 51 80 92

Averages 62.7 54 81 99.3

(5% level)-18.8
L.S.D.* (1% level)-28.6

Hamlin Sept. 24, 1954 105 108 113 115
Sept. 28, 1954 81 97 97 97
Oct. 12, 1954 92 93 102 109

Averages 92.7 99.3 104 107

L.S.D.* (5% level)- 8.2
L.S.D. (1% level)-12.2

(See explanatory note, Table 2.)


Dimensions.-Within reason, small rooms are easier to run
than big rooms. Square rooms are easier to operate than long,
narrow rooms. Rooms having low ceilings are easier to run than
rooms with excessively high ceilings.
On the other hand, traffic is easier to manage in larger rooms
and when motor trucks are used, high ceilings are an advantage.
In general, degreening rooms with capacities smaller than 400
boxes or larger than 1,000 boxes are not advantageous.
Exterior Walls.-Exterior walls should be heavy enough that
temperature changes do not cause condensation on the inner sur-
faces of the walls and on the fruit adjacent to the walls. If ex-
isting outside walls are of poor insulating quality (as for instance
when outside walls are sheet metal), a cheap and effective meas-

Florida Agricultural Experiment Stations

ure is to build an inner wall of canvas or light wallboard sepa-
rated from the outer wall by approximately 4 inches of air space.
Such light walls should be protected by rails or planks.
Interior Walls.-Interior walls can be of very light construc-
tion. Canvas curtains are extremely satisfactory. Such walls
are sufficiently gas tight to allow the necessary concentration of
ethylene to be established, and yet allow sufficient ventilation to
provide against carbon dioxide build-up. Another advantage of
such canvas walls is that they can be rolled up to the ceiling,
allowing for free traffic movement. Figures 13 and 14 show 2
packinghouses that make excellent use of such curtains. In the
example shown in Figure 13 solid walls beneath the slatted floor
divide the various "rooms." The degreening units are beneath
the floor. When they are not in use, the cylindrical "stacks" are
replaced with metal plates and the whole area becomes available
for other uses such as "set-back" space, i.e., for the assembling
of various varieties, grades and sizes of packed fruit.

Fig. 13.-Canvas-walled rooms in multiple units with slatted floor. The
various rooms are divided by solid walls below floor level. Above floor level
all walls are canvas and can be rolled up to give a large uncluttered area
that can be used for assembling packed fruit, etc. The workman is stand-
ing on the metal plate that covers a degreening unit when the central stack
is not in place. (Compare with Figures 6 and 7.)



Fig. 14.-Canvas rooms with a solid ceiling, a very efficient system.
Above: Note thermographs for continuous temperature recording and ethy-
lene trickle units beside them. The interior (below) shows the central unit
on wheels. It is supplied by a single steam coupling and an electric plug.
The ethylene pipe delivers just below the conical baffle or "diverter". This
type room is particularly well suited to the layout in Figure 10.

Bom =qW) ft-

Florida Agricultural Experiment Stations

Figure 14 shows a similar arrangement with solid floors and
portable degreening units. These are on castors and are con-
nected by a single steam line coupling and 1 electric plug-in.
Another, and even more simple, version has the heating unit at-
tached to the ceiling and the only equipment in the portable
stack is the fan. An extreme example of the use of canvas walls
is shown in Figure 15. In this type of set-up the "degreening
rooms" are tents suspended from the roof trusses by means of
wire cable. With such an arrangement the space above the de-
greening room is not available for a mezzanine floor as it is with
the types shown in Figures 9 and 10.
Doors.-At the time of the fruit fly infestation in 1929-30
many degreening rooms were built that were also designed for
vapor-heat sterilization. During the 1956-58 infestation vapor-
tight rooms were used for fumigation with ethylene dibromide.
Both these types of rooms had to have very tight-fitting doors,
many of which remain now that these rooms are used only for
degreening. Too tight construction accounts for more trouble
in degreening rooms than any other factor encountered by these
authors. Moreover, hinged doors are necessarily limited in size,
slow up traffic and invite accidents. Doorways in interior walls
are far better replaced by curtains. Curtains, however, are
hardly suitable for outside doorways, since in cold weather they
afford little protection against heat loss and invite condensation
on the fruit near the doorway. Hinge-type doors are frequently
used, but have the disadvantages mentioned above. Figure
16(a) shows the use of garage-type overhead doors. These al-
low for wide doorways and swing out of the way when not closed.
Figure 16(b) shows a very simple and inexpensive home-made
garage-type door suitable for degreening rooms.
Floors.-Floors have already been discussed in the section
on types of degreening rooms. Attention is drawn, however, to
the problems imposed by the type of clamp trucks used, i.e.,
power trucks or hand trucks. Hand trucks impose little addi-
tional strain upon the floors and hence can be disregarded when
selecting the type of floor. Motorized trucks are not well suited
to wooden floors in general or slatted floors in particular.
In older buildings trucks may go through the floor due to
unsuspected deterioration of joists or other supporting members.
Other more minor difficulties are that the vibration and flexing
of the floor boards tends to make the nail heads work up until

Degreening of Florida Citrus Fruits 35


Fig. 15.-Above: Tent-type degreening room. The "tent" is suspended
from the room trusses with wire cable. Below: Note that in this type of
room the conical baffle is attached to the center unit.

Florida Agricultural Experiment Stations

S.. ; -:
a- ----- ||


a1--- ;
.-...,* : ---- .....jg

Fig. 16.-Above: Garage-type overhead doors used on the outside walls
of degreening rooms. Note (top right) that canvas curtains are used for
the interior walls. Below: A very simple and inexpensive home-made ver-

(f -- _A L

Degreening of Florida Citrus Fruits

they catch on field boxes, cause workers to stumble, etc. Floor
plates covering degreening units, floor chain motors, etc., need
to be especially reinforced. If power trucks are to be introduced
into old degreening rooms, such matters need to be attended to
first. Power trucks are seldom fully successful on anything but
concrete or other rigid floors.

Ethylene.-Ethylene can be supplied either as the chemically
pure gas, purchased in cylinders, or, alternatively, by the old
method of using the fumes from the incomplete combustion of
kerosene. This latter method has little to recommend it, although
a few operators maintain that they get better results with kero-
sene fumes than with the bottled ethylene. It has been sug-
gested (97) that this may be due to the fact that the kerosene
method (whereby the fumes are blown through a duct from the
"smoke house" to the degreening rooms) necessitates the intro-
duction of considerable quantities of fresh air and hence ensures
continuous and adequate ventilation.
At one time ethylene was commonly administered by the
"shot method" in which a metered volume of ethylene is intro-
duced to the degreening room at regularly spaced periods, such
as every 5 or 6 hours. Today this method is seldom encountered,
being very largely replaced by the "trickle" method in which
ethylene is added in a continual slow stream, the gas bubbling
through water, thus affording a convenient visual check on
ethylene flow (5). Some operators use light mineral oil in their
trickle units instead of water, thereby preventing the growth of
molds and algae in these units.
Figure 17 illustrates a commonly used type of trickle unit.
In this type the ethylene passes through a diaphragm with a pin-
point hole (or "metering orifice"). This causes a back pressure
that forces up the level of the water in the manometer tube.
The purpose of this device is to provide a flow meter; the flow
rate is indicated by the height of the water column and interpre-
ted by means of a graph. In actual practice this flow meter at-
tachment is usually ignored and the rate of flow determined
merely by counting the number of bubbles per minute, in which
case a simple bottle and needle valve arrangement is adequate.

Florida Agricultural Experiment Stations




Fig. 17.-"Trickle unit" used for dispensing ethylene gas to a degreen-
ing room. Water or white oil is introduced through the funnel "F" until
the level is as shown. Ethylene from the main supply line enters through
the cut-off valve "C" and is regulated by the needle valve "R". The de-
livery pipe "A" is inverted so that the ethylene has to bubble through the
water. The metering orific "M" causes a back pressure resulting in a rise
in the manometer column proportional to the rate of gas flow. (Courtesy
Food Machinery and Chemical Corporation.)


Degreening of Florida Citrus Fruits

A simple and positive system is the use of a flow meter, of
which several types are available. If a flow meter is used, useful
figures to know are that 50 bubbles per minute on a typical trickle
unit is approximately equal to 12 cc. per minute and that there
are about 28,370 cc. in a cubic foot.
Whatever method of regulating supply is used, flow rate
should be adjusted to deliver the minimum amount of ethylene
that will do the job effectively. The amount will vary with the
size of the room. In theory, the amount of ethylene should be
varied if the room is only partially filled. However, the differ-
ence is minor and is probably best ignored.
A rough approximation is that the amount of ethylene needed
will be in the neighborhood of 1 bubble per minute for each 10-
box 5 capacity. In rooms with strong continuous ventilation,
more may be needed. In rooms with little ventilation, or in very
tightly constructed rooms, less ethylene may be needed.
The purpose in supplying ethylene is to build up a certain
minimum concentration of ethylene in the atmosphere around
each fruit. In practice, considerably more than the minimum
amount of ethylene is usually used, on the unfortunate theory
that "if a little is good, a lot must be better." Such an attitude
is encouraged by the low cost of ethylene 6.
The sooner the minimum concentration (which is somewhere
near 1:100,000) is reached, the sooner degreening will start.
Until then the fruit is suffering the ill effects of being held in a
humid atmosphere at a high temperature without benefit in the
way of degreening. If gas flow is sufficient to build up this con-
centration rapidly, it will probably supply excessive amounts of
ethylene thereafter, while slower flow rates take excessively long
to build up this minimum concentration. Hence the logical pro-
cedure is to supply an initial quantity sufficient to build up the
minimum concentration needed, and then have the ethylene
delivery set at a rate sufficient to maintain this level. The initial
amount added should be approximately 1/50 of a cubic foot for
every thousand cubic foot capacity. For example: in a room
40 x 25 feet with an 8-foot ceiling and 2 feet beneath the slatted
floor, total volume is 10,000 cubic feet. In such a room 1/10 of
"Throughout this bulletin the term "box" refers to the standard field
box as defined in the Florida Citrus Code (17). Its internal volume is 4,800
cubic inches (2.232 U. S. bushels).
6 Ethylene retails at approximately $30 for 25 lbs. At this rate the
ethylene necessary to degree 600 boxes for 72 hours would cost less than
250. Used at a rate of 60 bubbles per minute, a 25-lb. cylinder of ethylene
can deliver continuously for a year.

40 Florida Agricultural Experiment Stations


Fig. 18.-Exterior (above) and interior (below) of a masonry "smoke
house" in which kerosene burners generate ethylene-rich fumes to be car-
ried to the degreening rooms by a forced ventilation system.

Degreening of Florida Citrus Fruits

a cubic foot of ethylene will raise the concentration to 1:100,000.
This quantity can be measured very approximately by using the
water column and chart method; e.g. consulting the manufac-
turer's chart for a typical unit, it would take 18 minutes at 3
inches water pressure. Using such a trickle unit, a very rough
approximation is to raise the water level to 3 inches and hold it
there 1 minute for each 100-box capacity. Thereafter the flow
should be cut to the minimum necessary to maintain effective
degreening, e.g. the 1 bubble per minute per 10-box capacity, as
recommended above.
When kerosene fumes are used as the source of ethylene,
Florida regulations (59) prescribe that the burners shall be ex-
ternal to, and at least 15 feet from, the coloring rooms. This
requirement is fulfilled by having a stone or masonry "smoke
house" in which the burners are situated. Such a structure is
shown in Figure 18. A baffle over each wick assures a smokey
flame with fumes rich in ethylene. These fumes are then blown
through ducts to the coloring rooms by means of forced ventila-
tion. This is why it is suggested above that some of the benefits
attributed to kerosene may be due to the good ventilation in-
herent in this method. Although the possibility exists that
there may be some other beneficial component of kerosene fumes,
there is no positive evidence of this.
Humidity.-Accurate regulation of humidity is difficult; so
much so that some operators do not attempt to regulate humidity
during degreening.
Most degreening rooms are equipped with 6 types of con-
trols, namely: fan; ethylene delivery; radiator ("dry steam");
steam nozzles ("wet steam"); water spray; and ventilation
openings. Adjustment of any of these except ethylene delivery
will affect relative humidity within the degreening room. More-
over, the harmful effects of using too low a humidity depends
greatly on the amount of air circulation. The higher the rate
of air circulation, the more harmful the effects of too low a hu-
midity level. Shrivelling (and to some extent peel breakdown)
is a function of both humidity and rate of air flow over the fruit.
The rooms should be run in such a manner that humidity is
high enough to restrict shrivelling, but without the fruit ever
becoming wet. Wet fruit should never be brought into a de-
greening room; but sometimes this may be unavoidable, as when
trucks coming in from the grove are caught in a rain storm.
When this happens the fruit should be dried as rapidly as pos-

42 Florida Agricultural Experiment Stations

sible. To do this the air needs to be moved rapidly, changed fre-
quently and (if below 85 F.) heated. This is best done by load-
ing the room, turning on the fan and radiator and leaving the
ventilators and doors open until the standing water has dried
off the surface of fruit.
Once the fruit is dry, the room can be closed and the ethylene
turned on. To avoid the possibility of condensation, a tempera-
ture difference of about 2 to 3 degrees should be maintained
between wet and dry bulb temperatures, e.g. wet bulb 82 F. and
dry bulb 85 F. If the temperature spread increases beyond
this, moisture should be added. If the temperature is too low,
then moisture is best added by a steam jet. If the temperature
is too high, then moisture should be introduced by the water
spray. This also has a slight cooling action due to the absorp-
tion of heat in the evaporation of water. This cooling effect is
unlikely to be more than 1 degree, F.
Any regulation of the controls will take an appreciable time
to change the atmosphere in the degreening room. Hence the
degreening room conditions should be rechecked a half hour or
so after each adjustment.
When in doubt, it is usually better to allow the humidity to
fall a little too low rather than to let it get too high with conse-
quent risk of condensation and wet fruit. An exception to this
would be when degreening fruit known to be susceptible to peel
Temperature.-In hot weather fruit may come in at tempera-
tures very much above 85 F. When this happens, it is best to
air out the room after loading and, if possible, not start degreen-
ing until the fruit temperature is lower. Once the degreening
room is closed, the temperature can be expected to rise to slightly
above that of the temperature in the packinghouse, due to the
heat of respiration of the fruit.
If the temperature is below 850 F., it is usually raised by
means of the radiator (if the difference between wet and dry
bulb temperatures is narrow) or the steamjet (if the wet bulb
temperature is too low).
When in doubt, it is better to have the temperature a little
too low, rather than a little too high. At the Citrus Experiment
Station the best degreening temperature has sometimes been as
low as 80 F. It has never been over 85 F. (23).
Early in the season a temperature as low as 85 F. is often
impossible to maintain due to (1) high air temperatures; (2)

Degreening of Florida Citrus Fruits

high fruit temperatures (a fact that is often overlooked is that
fruit that has been exposed to the direct rays of the sun may
come in at temperatures very much higher than that of the sur-
rounding air) ; (3) heat of respiration. In consequence degreen-
ing rooms may go to as high as 1000 F., even without added heat.
Such very high temperatures prolong the degreening period
(which is already unduly long at this season) and consequently
decrease the keeping quality of the fruit. Because of this it
might well pay to have some of the degreening capacity refrig-
erated. Since packinghouses run only intermittently in the
fall, for those having precooler rooms or other refrigeration it
might be quite practical to devise a system whereby the com-
pressor system could be used to cool some of the degreening
rooms when such a need becomes pressing.
Efficient temperature control involves maintaining correct
temperatures throughout the whole room at all levels. This in
turn is quite largely dependent on efficient air circulation.
Air Circulation.-The efficiency of air circulation is largely
determined by the type of room used and the equipment installed
in it. Once a room is set up, comparatively little can be done
to regulate air circulation without modification of the physical
plant. Hence it is essential that several simple rules be followed
in the installation of degreening rooms.
A common misconception is that forced air circulation neces-
sarily involves blowing or forcing the air through the stacked
fruit. It is often difficult and inefficient to blow air through a
stack of fruit. On the other hand, it is easy to draw large vol-
umes of air through stacked fruit by establishing slight differ-
ences in atmospheric pressure on 2 sides of the fruit. When
this is done, the air moves readily through the stack in an in-
evitable tendency toward equalization of the pressure. For the
fan or fans must tend to draw their air from one side of a stack
of fruit and deliver it to another side. Fans that merely churn
up the air over the fruit are almost useless.
Efficient air circulation involves having adequate fan ca-
pacity, but just how much fan capacity is adequate will vary with
the type and size of the degreening room. One way of expressing
fan capacity is in terms of cubic feet of air per minute (C.F.M.)
circulated per thousand cubic feet volume within the degreening
room (when empty). Efficiently functioning degreening rooms
in Florida packinghouses have had between 625 and 1,500 C.F.M.
per 1,000 cu. ft. air volume. Baier and Ramsey (1), who made

44 Florida Agricultural Experiment Stations

a very thorough study of fan capacities for California degreen-
ing rooms, state that one 1,500 C.F.M. fan is necessary per 200
square feet of floor area. This is approximately 750 to 1,000
C.F.M. per 1,000 cu. ft. volume within the degreening room. Ex-
pressed another way, this is approximately 7.5 to 10 C.F.M. of
fan capacity per 1 box capacity in the degreening room.
The USDA regulations for fruit fly fumigation rooms (50)
stipulate fan capacity to give an air change once per minute
based on the air volume of the empty room, i.e., 1,000 C.F.M.
per 1,000 cubic feet capacity. (This ensures continuous circula-
tion of the heavy ethylene dibromide vapor). When adapting
existing degreening rooms to serve as fumigation chambers, this
increased fan capacity considerably, resulting in a remarkable
increase in efficiency when these same rooms were then used
for degreening.
It must be borne in mind, however, that the harmful effects
of too low humidity are exaggerated in a degreening room in
which rate of air circulation is high. When air circulation is
enough to ensure the maximum rate of degreening, then hu-
midity level must be kept as high as possible without involving
Ventilation.-As has been mentioned already, ventilation can
be either continuous or intermittent. The larger the load of fruit
in relation to the air space in the degreening room, the more need
for adequate ventilation.
Winston and Tilden (97) and Rebour (58) (whose account
is probably largely based on Winston's reports) have advised a
combination of both continuous and intermittent ventilation,
but the present writers feel that in well run degreening rooms
1 method or the other should be adequate.
Continuous ventilation, although less common, is the easiest
to run, and in experiments at Lake Alfred has been found to be
as good as, if not better than, intermittent ventilation. In con-
tinuous ventilation an opening on the vacuum side of the fan
draws in fresh air continually. Three such arrangements can be
seen in Figures 4, 6 and 19. Since the total volume of air in the
room has to stay approximately constant, an equivalent volume
of stale air escapes from the room through any openings avail-
able. In very tightly constructed rooms (such as fruit fly fumi-
gation rooms), it might be necessary to make a special opening,
but in rooms with canvas walls or ill-fitting doors no special pro-
vision is necessary to allow for escape of stale air.

Degreening of Florida Citrus Fruits

In some types of degreening rooms arrangements for con-
tinuous ventilation can be set up by running a light metal pipe
from the outside to an area just behind the fan. Such a pipe or
duct should be equipped with an adjustable damper. The bulk
degreening system is particularly well suited to a continuous
ventilation system. Figure 19 shows the simple adjustable open-
ing for such ventilation. For any continuous ventilation system
the size of the opening is dependent upon the size of the room,
the load of fruit that it holds, the vacuum created by the fan
and other minor factors such as the type of fruit in the room
(oranges, for example, respire more rapidly and hence put out
more carbon dioxide than do grapefruit).
Because of such factors the intake has to be set by trial and
error for any given room. In checking rooms running success-
fully on the continuous ventilation system, rates of fresh air in-
take have been found between 1.4 percent and 3.6 percent of the
total volume of the room per minute. If a velometer or anemom-
eter is available, such a ventilation opening should be set to draw
in about 2 percent of the total volume of the room per minute.
Adjustment can be made thereafter to get maximum degreening
rate for that particular room. Such a system is a little trouble
to set up, but once in operation it runs automatically.


Length of Opening
in Inches


Setting finally adopted.

Area of Opening
(Square Inches)


Percent CO in Degreening


A great deal of guess work can be eliminated by use of a
simple gas analyzer of the "Orsat" type. These are inexpensive,

Florida Agricultural Experiment Stations

can be operated without special training and can read carbon
dioxide to 0.1 percent. Table 7 shows the readings obtained in
adjusting the ventilation opening (shown in Figure 19) on a bulk
degreening bin. The setting determined for 1 bin could be used
on all the other bins of identical pattern. The following year,
however, shrinkage of construction materials had provided
enough accidental ventilation that the opening had to be reset
to a smaller size.
Intermittent ventilation involves no initial experimentation
to arrive at the correct setting, but makes continual demands
upon labor as long as the degreening rooms are running. Meth-
ods differ widely in detail, but all involve opening the degreening
room doors or curtains at intervals throughout the degreening
period to ventilate the rooms. Sometimes portable fans are used
to blow fresh air into the rooms. This should not be necessary
for rooms of 400 boxes capacity or less, but might be advan-
tageous in large rooms. The permanent fan or fans should be

Fig. 19.-Adjustable ventilation opening on bulk degreening bins. Three
bins are operated from a single conditioning unit, so this opening supplies
fresh air and reduced CO. level in 3 bins holding a total of about 600 boxes
of fruit.

I W' 1 ,o
ft .tft- .-

Degreening of Florida Citrus Fruits

left running during the ventilation period to facilitate air ex-
Hardening-off.-Certain crops, particularly of grapefruit,
sometimes develop a form of rind breakdown known as pitting.
This is aggravated by various forms of handling and can be se-
rious enough to cause considerable concern. In order to mini-
mize pitting of grapefruit, most operators prefer to let fruit
stand for a "hardening" period after degreening and before it
is run over the packinghouse machinery. With some varieties
color change can be expected to go on after removal from the
presence of ethylene. When this is the case, a hardening period
can be given without slowing up packinghouse operations by
opening up the degreening rooms before the degreening process
is completed. The fruit can be either left in the degreening room
or, if the degreening capacity is limited, set out on the packing-
house floor.
In experiments with Florida citrus, color change in Duncan
grapefruit continued virtually uninterrupted for at least 24
hours after removal from the degreening rooms. Color change
in Hamlin oranges ceased within the first 6 hours after removal
from the ethylene atmosphere. Valencia oranges continued to
change color for about 24 hours (see Figure 20). This is at vari-
ance with a report from California that Navels continued to
color after removal from the degreening room, but Valencias
did not (1).
Although there seems to be a fair measure of agreement
among packinghouse operators with regard to the possible ben-
efits of "hardening-off" grapefruit, the situation with regard to
peel injuries of oranges is so much more complex that this is
discussed in detail in the section on injuries associated with de-
greening. In general, "hardening off" of oranges is not advised.

This bulletin is concerned with the handling of the fruit after
it has been grown. However, cultural methods have so great an
effect upon degreening that they should be considered in any
comprehensive discussion and no comprehensive review is known
to these authors. Frequently difficulty in degreening, incor-
rectly attributed to inefficient packinghouse procedures, is trace-
able to the grove.
The effect of various grove practices upon degreening is fol-
lowed closely in the packinghouse research program at the Citrus

u 50


40 30 20 10 0 10 20 30 40

Hours Prior to Leaving Degreening Room Hours After Leaving Degreening Room

Fig. 20.-Rate of degreening of Hamlin and Valencia oranges and Duncan grapefruit before and after re-
moval from a degreening room.

Degreening of Florida Citrus Fruits

Experiment Station and certain tendencies are showing up con-
sistently enough to merit mentioning. In addition, some infor-
mation bearing on this problem has been published and refer-
ence to such literature may prove helpful.
Spray Program.-The tendency of oil sprays to delay de-
greening is widely known, although the seriousness of this effect
is often not realized. As early as 1929 Yothers and McBride
(102) reported that oil sprays delay the maturing of citrus
fruits. Thompson (83, 86) and Winston (98), in 1942, reported
that oil sprays cause serious retardation of ethylene degreening.
Sites and Thompson (72), in 1948, stated that, "An oil emulsion
spray may have an effect on the degreening of fruit 4 or 5 months
after the application if the nights are warm during October and
November." They go on to say, "From the standpoint of timing
oil sprays to obtain the least retarding of degreening of early
varieties, the same dates should be observed as with timing the
sprays to have the least effect upon solids."
With the advent of parathion, an alternative scalicide was
available which had no discernible effect upon subsequent de-
greening. Table 8 shows data taken from a table of Thompson,
Griffiths and Sites (86). Twelve weeks after sprays were ap-
plied, marked differences in degreening were still apparent be-
tween the oil-sprayed and the parathion-sprayed fruit. This was
so marked that after 48 hours' degreening, the parathion-
sprayed fruit had more than 16 times as high a percentage of
well-colored fruit as did those receiving the oil spray.

AND SITES (86).)

Time in Well Colored Fairly Well I Slightly Colored
Degrening I Colored to Green
Room Oil Parathion** Oil Parathion || Oil Parathion
48 hours ......... 4 57 71 43 25 0
65 hours .......... 16 77 84 23 0 0
72 hours ........ 62 97 38 3 0 0

Oil emulsion, 1.3 percent actual oil.
** Parathion (15 percent), 1.66 lbs. per 100 gallons.

Thompson, Griffiths and Sites (85) and Thompson and Des-
zyck (84) investigated the effect of very small quantities of oil

50 Florida Agricultural Experiment Stations

used in conjunction with parathion, but found that, when used
in September, sprays as little as 0.4 percent actual oil delayed
degreening. In 1953 Harding and Fisher (31) reported that not
only did parathion-sprayed fruit degree earlier than fruit
sprayed with oil emulsion, but that the resultant color was a
deeper, more reddish orange.
Malathion is another scalicide that does not affect subse-
quent degreening (84). In our checks of Ruby Red grapefruit
from scalicide spray plots, the exterior red blush is sometimes
much more pronounced in the fruit from plots that received
parathion or malathion without oil.


Spray Date Hours to Degreen
(1956) Picked* Nov. 13 J Picked** Nov. 26 Picked** Dec. 10
June 15 -......... 61 32 10
June 29 .........- 63 36 14
July 17 ............ 61 38 13
August 15 ...... 72 41 12
August 31 ...... 66 49 15

Final color on all samples tended to be dull and yellowish.
** Final color usually reddish orange.

That such effects do not always show up consistently is un-
derstandable, since the response of the fruit to degreening is
affected not only by the type of scalicides used but also by the
number and date of applications and the date of picking. This
latter point is illustrated in Table 9, which shows the time taken
to degree tangerines from one of W. L. Thompson's oil spray
timing experiments at the Citrus Experiment Station. All these
tangerines were from plots sprayed with 1 percent oil emulsion,
the only variable being the date of application. The samples
picked November 13, 1956, showed no consistent effect of date
of spray application on subsequent degreening. The samples
picked November 26 showed a consistent relationship, the later
the spray application the longer the fruit took to degree. A
still later picking, December 10, showed little correlation be-
tween spray date and rate of degreening, as by that time these
samples needed only over-night degreening. This, incidentally,

Degreening of Florida Citrus Fruits

is a remarkably rapid recovery from oil sprays applied so late
in the season.
The slowing up of degreening by summer oil sprays is well
known, but nevertheless many early season troubles with de-
greening still trace back to oil sprays applied too late for subse-
quent early picking. Nor is this effect confined to Florida. Re-
ports from California (3, 54, 71, 81, 82) state that even their
very light, highly refined spray oils have been found to cause
serious delay in the degreening of Valencia and Navel oranges
as well as of lemons.7 An excellent and detailed report from
South Africa (80) states that oil sprays applied in April delayed
degreening of Valencia oranges picked in September. On Navels
the effect was even more marked; a single oil spray had a statis-
tically significant effect in delaying degreening in 2 successive
Since summer oil sprays also delay maturity in terms of sol-
uble solids (corresponding approximately to sugar concentration
in the juice) (34, 72, 73, 81, 82, 84, 102), they are always risky
on fruit that is to be harvested for the early market.
A minor problem in Florida, but 1 that is often erroneously
attributed to degreening room conditions, is "water spotting"
of Navel oranges. This is discernible at time of picking, but is
seldom noticed until after degreening which, along with other
packinghouse treatments, intensifies the trouble. So few Navels
are grown in Florida that no systematic study of this trouble has
been made here. However, reports from California (46, 64)
indicate that not only is this trouble aggravated by oil sprays
but (under California conditions) the effect can be still discern-
ible 7 months after spraying.
Scale Insects.-Infestations of scale insects are directly re-
lated to the effectiveness of the spray program and hence have
both a direct and an indirect effect upon degreening. Purple
scale (Lepidosaphes beckii Newm.), and chaff scale (Parlatoria
pergandii Comst.) greatly retard degreening. A single scale
will arrest degreening of the rind immediately around it. A
considerable scale population upon a fruit will completely stop
degreening. Purple scale is readily visible and the reason for
the green areas on the fruit is apparent. Chaff scale is much
harder to see and often cause green spots (particularly on tan-
gerines) sufficient to downgrade the fruit without the reason
for these blemishes being readily apparent. Thompson, Pratt

Ethylene degreening of Florida lemons is not advised.

52 Florida Agricultural Experiment Stations

and Johnson (87), in discussing the effect of these 2 scale in-
sects on degreening, say, "Control measures should be taken as
early as possible, especially on tangerines, because it is not known
how long before harvest scale must be killed to stop their effect
on degreening."
Since, as is stated above, it is well known that purple scale
and chaff scale delay or arrest degreening, it is often presumed
that this is true of all scale insects. The Florida red scale (Chry-
somphalus aonidum L.) is a common pest that does not affect
Fertilization.-There is an increasing amount of evidence
that the type and time of application of fertilizers can affect the
degreening of citrus fruits. Most such reports deal only with
color break on the tree, rather than in the degreening room, but
there is no evidence that these are separate phenomena.
Reuther and Smith (62) report that heavy applications of
potassium delay maturity of Valencia oranges both in terms of
ratio and in regard to external color, the larger fruit still being
green in May. The same authors (61) and also Winston (99)
and Winston and Lutz (95) report that heavy applications of ni-
trogen also tend to delay color break.
Reuther and Smith (61) found that the effect of nitrogen
upon fruit color was less than that of potassium. The effect of
the 2 was accumulative, an effect that Tomkins (88) has reported
with regard to "ratio." That this relative effect of these 2 ferti-
lizers is not necessarily constant is shown by the results in Table
10 giving data obtained by these authors using Valencia oranges
from some of the Indian River fertilizer plots of H. J. Reitz.
From this table it will be seen that increasing the total amount
of nitrogen sharply decreased the proportion of oranges meeting
the color requirements for No. 1 grade. Ethylene degreening,
although it raised the pack-out generally, did not have a great
deal of effect on fruit from the high-nitrogen plots. In this
experiment the effect of high potash levels was ill-defined.
Reuther and Smith (61) reported that Valencia oranges from
high-phosphate plots "regreened" to a much greater extent than
those from low-phosphate plots. This might account for the
observation by these authors that in 1956-57 (a bad regreening
year) color at picking and after degreening was very much better
in fruit from a fertilizer experiment in which phosphorus was
omitted, as compared to fruit from a treatment in which phos-
phorus had been used but potash was omitted.

Degreening of Florida Citrus Fruits


Nitrogen as Pounds N per Tree per Year
1.2 1.8 2.4 1.2 1.8 2.4
Potash as Pounds of
PotaO erPounds ofTree Percent of Sample Meeting Color Requirement
per Year Tfor U. S. No. 1 Grade*

Before Degreening After Degreening

0 68.8 44.9 28.0 85.1 56.3 51.0
2.4 72.0 36.0 25.0 84.0 57.4 46.9
4.8 58.8 50.0 25.5 80.4 58.8 40.4

Each figure is the average of samples taken from 4 or more randomized plots.

In view of these findings, it is inevitable that the total amount
of mixed fertilizers applied to the tree should affect fruit color
and subsequent degreening. This has been confirmed by these
authors when degreening Valencia oranges from the Indian River
fertilizer plots of H. J. Reitz. A summary of the results ob-
tained is shown in Table 11; the color of the fruit samples are
indicated by the proportion of each sample meeting the require-
ments for No. 1 grade (92) both before and after degreening.
This was a particularly bad year with regard to color and it will
be noted that, with fruit from both the medium and high rates,
color after degreening was worse than in the fruit from the low
rate plots prior to degreening. Such differences could be ex-
pected to be very much less in a season such as 1957-58 when
cold weather hastened color break and slowed regreening in the


Fertilizer Percent of Sample Meeting the Color
Application Requirement for U. S. No. 1 Grade*
8-4-10-7 Mix Before Degreening I After Degreening

4 lbs. per tree twice a year .... 63.3 86.9
13 lbs. per tree twice a year .... 45.4 60.1
22 lbs. per tree twice a year -.. 41.3 59.4

*Each figure is the average of samples taken from four randomized plots.

Florida Agricultural Experiment Stations

The timing of fertilizer applications also affects degreening
and other criteria of maturity. Reuther and Smith (63) re-
ported on the effect of the number of fertilizer applications and
the season at which they were applied. It was found that early
disappearance of green color is favored by a single fall applica-
tion of nitrogen rather than by applying the same total quantity
of nitrogen in the form of 3 (spring, fall and winter) applica-
tions. This parallels the findings of Bahrt and Roy (2) and Roy
(69), who report that when total potash requirement was applied
in the fall, rather than in the customary 3 applications, legal ma-
turity (in terms of ratio) of Parson Brown oranges was advanced
by 2 to 3 weeks. They do not report on the effect upon external
color or degreening, but the findings of Reuther and Smith (63)
would indicate that these effects are related.
Reitz (60) reports that the color of Indian River Valencia
oranges fertilized only in October was outstanding in December
and January; however, during February this difference dimin-
ished so that by harvest regreening had obliterated the differ-
ences between the treatments. This affords another example of
how the apparent effect of a grove treatment on color break may
be affected by the date of picking. (Compare with the results of
oil sprays on tangerines as shown in Table 9.)
Martin (49), reporting on Marsh grapefruit grown in Ari-
zona, found that color break was accelerated by a low nitrogen
content of the tissues of the tree, regardless of whether this
effect was due to reduced fertilization, application of nitrogen in
winter rather than in spring or summer or competition for nitro-
gen by summer cover crops.
Trace Element Nutrition.-In the course of checking several
hundred fruit samples from trace element experiments,8 no
consistent effect on fruit color or degreening has been discerned.
Irrigation.-In reviewing the above papers and experiments
on sprays and fertilizers, it is apparent that those factors that
tend to delay degreening are the same factors that tend to delay
maturity in terms of other standards such as ratio and solids.
This affords some degree of confirmation of the observation com-
monly made by packinghouse operators that "high-solids crops
degree easier than low-solids crops." With irrigation no such
clear-cut relationship is apparent and hence the problem has to
be approached with particular caution.

8 Acknowledgment is made to Drs. H. J. Reitz, E. J. Deszyck and J. T.
Griffiths, from whose experiments these samples have been obtained.

Degreening of Florida Citrus Fruits

One of the most difficult problems in early season degreening
is associated with handling a crop set from a scattered or irreg-
ular bloom period. The authors have seen such a crop of Parson
Brown oranges picked in the first week of November pack out as
low as 20 percent due to failure to degree properly. Such a low
pack-out with very early season fruit is particularly costly due
to the poor market for packinghouse eliminations at that season
(21). Sites, Reitz and Deszyck (75) report that, in experiments
with Marsh and Silver Cluster grapefruit, late or scattered bloom
could be controlled to some extent by judicious irrigation. Thull-
berry (89), writing some 6 years later, stated that growers wish-
ing to raise an early crop of grapefruit sometimes start irrigation
in December to force an early bloom. As Turnbull (90) has
pointed out, such a practice is hazardous in the event of a severe
Other Factors Affecting Degreening.-Other factors affecting
color break and degreening include some that are not readily
controlled by the grower. Despite the numerous publications
dealing with the effect of rootstocks upon other aspects of fruit
quality, there is very little known of their effect upon color and
color break. Studies such as those of Harding (30, 31, 32, 33)
indicate that rootstock influences follow the general tendency
for vigorous vegetative growth (such as is characteristic of
rough lemon stock) to be associated with delayed color break
and slow degreening. This observation appears to be confirmed
by observations made on the samples from various rootstocks
examined periodically in the Citrus Station packinghouse.
Climate and- seasonal differences have well defined effects
upon color break and degreening. Stearns (77) and Stearns and
Young (78) carried out very careful studies of the relationship
between climatic conditions and color break. With Hamlin, Par-
son Brown and Pineapple oranges they found that there was no
consistent color break until minimum temperatures dropped be-
low 55 F. and thereafter the extent of color break was related
to the duration and severity of the periods when minimum tem-
peratures were below 55 F. They also reported that the dura-
tion of ethylene degreening necessary to degree oranges was
related to previous climatic conditions, even when considering
oranges having the same degree of green color.
These same authors also investigated color break in Marsh
and Duncan grapefruit but could find no such correlation with
climatic conditions as they found with oranges. Color break

56 Florida Agricultural Experiment Stations

tended to be gradual and fairly consistent throughout the fall
and early winter. Caprio (8, 9), reporting on a 28-year study of
regreening of California Valencia oranges, states that serious
regreening was related to delayed blooming date, immaturity at
onset of winter and warm weather in the several months prior
to harvest.
Arsenic sprays are often erroneously credited with affecting
degreening. Since these are used to hasten maturity of grape-
fruit, it is sometimes assumed that they must have an effect
upon color break. Experiments at the Citrus Experiment Sta-
tion (16) indicate that arsenic sprays have no consistent effect
on subsequent degreening. This confirms Juritz' (44) observa-
tion that arsenical sprays did not affect external appearance of
South African oranges.

Discussion of degreening methods throughout this bulletin
has of necessity involved the mention of the various injuries and
diseases that are associated, one way or another, with degreen-
ing. However, these troubles are often the cause of much con-
troversy, much of which is due to imperfect understanding of
factors that cause them.
"Gas Burn" or "Ethylene Burn" of Oranges and Grapefruit.-
Several distinct types of epidermal injury are commonly included
in the terms "gas burn" or "ethylene burn." The commonest

Fig. 21.-So called "gas burn" on early season Hamlin oranges.
The lesions are usually brown and slightly sunken.

Degreening of Florida Citrus Fruits

2 are a brown spotting that may appear as either scattered pits
or else as widespread, slightly sunken discolored areas (Figure
21) and "ring burns" which are discolored circular injuries that
sometimes occur at the points of contact between the individual
fruits (Figure 22).

Fig. 22.-"Ring burns." Note the circular discoloration formed where
fruit have been in contact with one another.

On oranges and grapefruit such blemishes are seldom, if
ever, initiated by ethylene, although it may be a contributing
factor. Very definite ethylene injury has, however, been found
on Temples (22) and, to a lesser extent, tangerines (24).
Rose et al (66) state categorically that such injuries are due
to degreening room conditions other than ethylene. Later re-
search (22, 24) would indicate that this statement is still true,

Florida Agricultural Experiment Stations

with certain reservations. They attribute such so-called "gas-
burn" to low humidity in the degreening room. Table 12 shows
the "gas burn" found in a series of experiments with immature
Hamlins. The fruit shown in Figure 21 are from this same ex-
periment. The amount of this injury was related to degreening
temperature and to picking date. Raising the temperature from
850 F. to 1000 F. caused approximately 1,000 percent increase in
the amount of "gas burn." Comparing the samples degreened


Picking Date

September 26, 1952

October 1, 1952 ......

Relative I Tempera-
Humidity* | ture oF.







Peel Injury |




Hours to




October 6, 1952 ...... Low 70 0 88

Normal 70 0 85

High 70 0 85

Normal 85 0 66

October 13, 1952 .... Normal 75 0 63

Normal 85 0 42.5

Normal 95 0 48

October 16, 1952 ... Normal 80 0 45.5
Normal 85 0 41

Normal 90 0 42

Low-60-70 percent; Normal-80-90 percent; High-90 percent and up.
** All degreened to the same color as judged with a visual comparison colorimeter.
(40 percent green = Munsell g Y 8/10 (52).
All samples received ethylene and at the same rate.

Degreening of Florida Citrus Fruits

at 85 F. and normal humidity (which was used as the control
treatment for all picks), the amount of "gas burn" decreased as
the fruit approached maturity, dropping from 4.8 percent for the
September 26 picking to zero for the October 6 picking. No cor-
relation was found with humidity. (But note that other types
of peel injury on oranges, as discussed below, are closely related
to humidity.)
Table 13 shows results from another experiment in which
washed and unwashed fruit were held in the degreening cabinets
with and without ethylene. In this experiment, which was with
immature fruit also, the most serious amounts of this so-called
"gas burn" occurred with unwashed fruit. In another experi-
ment washing prior to degreening reduced "gas burn" of Hamlin
oranges from 17 percent to 1 percent and from 18 percent to zero
for Navel oranges.


Percentage of Fruits Injured
Treatment Date Hamlin Oranges Duncan Grapefruit
(1954) With No With No
I IEthylene Ethylene Ethylene Ethylene
Washed .... Sept. 13 2 0 0 0
Sept. 16 0 0 8 0
Sept. 24 0 0 0 0
Averages 0.7 0 2.7 0

Unwashed Sept. 13 25 18 0 0
Sept. 16 25 0 2 0
Sept. 24 0 0 0 0
Averages 16.7 6 0.7 0

Hence it would appear that much of this so-called "gas burn"
is due to the "burning" action of dirt, fertilizer dust, spray resi-
dues, etc., which dissolve in water on the surface of the fruit,
and resultant solution gradually grows more concentrated as it
evaporates. This would agree with the observation by Stevenson
(79) that spray residues on Australian citrus commonly cause
blotchingg" during degreening. Either this is not the sole cause,
or else it is indistinguishable from some less common injury

Florida Agricultural Experiment Stations

since, although this injury can occur in the absence of ethylene,
ethylene often increases its severity. This is apparent in the
data presented in Table 13. Moreover, as in Table 13, in these
experiments occasional apparent "gas burn" is encountered on
washed fruit, indicating that dirt is not the sole cause.


Days in Days from
Degreening Ethylene Entering Degreening Cabinet
Cabinet 3 Days 6 Days) 9 Days 18 Days

Percentage of Fruits Injured*
1 ...................... Normal Concentration I 0 0 4 6
2 .............-.. .I Normal Concentration 0 16 30 54
3 ...................... Normal Concentration 2 40 64 74
3 (Control) None 0 I 0 0 0

For type of injury see Fig. 23.

"Gas Burn" or "Ethylene Burn" of Temples.-A very serious
"burn" or skin breakdown of Temples caused by ethylene (Figure
23). The amount of this injury is related to both the ethylene
concentration used (Figure 24) and the duration of exposure to
ethylene (Table 14). A factor that makes this trouble hard to
recognize is its delayed appearance. It seldom appears until at
least 2 days after removal from the degreening room and can
continue to appear for as long as 18 days from picking (Table
14). Because of this, Temples shipped in apparently excellent
condition can develop severe rind breakdown during shipment

Fig. 23.-Peel breakdown on Temples caused by ethylene.
(See also Figure 24 and Table 14.)

Degreening of Florida Citrus Fruits

and marketing. In view of this it has been suggested that ethyl-
ene degreening of Temples might well be prohibited (22).

12 6 3

Fig. 24.-Peel breakdown of Temples held for 2 days at 850 F. in vari-
ous concentrations of ethylene (6 bubbles per minute approximates normal
concentration) and held thereafter at 700 F. Note that in all ethylene-
treated samples, fresh injury continues to appear to or beyond 16 days from
picking (i. e., 14 days after leaving the degreening room). From Grierson
and Newhall (22). (See also Figure 23 and Table 14.)

Handling Damage of Tangerines.-Tangerines that have been
degreened become particularly sensitive to various forms of
handling damage. This is illustrated by the results from a com-
mercial packinghouse presented in Figure 25. The damage pat-
tern shown here corresponds closely to that in many experiments
carried out at the Citrus Experiment Station. Tangerines that
have been degreened behave quite differently from those that
have not. Not only do degreened tangerines suffer more damage
due to the polisher brushes, but this damage is not repaired by
due to the polisher brushes, but this damage is not repaired by

6%(1 l




.0 0
o 2


. 20

lI I I I I I 1

Sampling positions along Tangerine line

-o' o (.
.S' SIC a .. C
aE E .

o 4O C

Fig. 25.-Handling damage in degreened and non-degreened tangerines processed on a tangerine line in
a commercial packinghouse and held thereafter at 70' F.


- Degreened

Not degreened




Fig. 26.-Above: Injury to tangerines due to accumulative effect of
degreening, polishing and waxing fruit picked without a good color break.
This injury appeared approximately 1 week after picking. Below: Injury
to tangerines picked with a full orange color and then held in the degreen-
ing room while the greener fruits of the same picking were degreened.
Photographed 1 week from picking. From Grierson and Newhall (25).

64 Florida Agricultural Experiment Stations

waxing, as happens with the non-degreened tangerines. Indeed,
additional damage sometimes occurs that is attributable to the
cumulative effects of grove conditions, degreening, polishing and
Figure 26 shows how this injury, which is sometimes called
"zebra skin," takes the form of dark sunken areas that follow
the divisions between the fruit segments. The discolored fruit
also develop an objectionable flavor and soon succumb to decay.
This type of injury shows up several days after packing and
hence is not often seen in the packinghouse.
The occurrence of zebra skin has been found to be related
to the moisture conditions in the grove, the quantity of ethylene
used, the duration of the degreening period and the color of the
tangerines prior to degreening. A bad outbreak can be expected
when degreening tangerines from groves where rain or irriga-
tion has maintained a high moisture level. High ethylene con-
centrations or prolonged degreeing followed by rough handling,
particularly polishing, accentuates this disorder. Losses are apt
to be higher in fully colored tangerines that are mixed in with
green tangerines during degreening and in tangerines that have
no color break at picking. For this reason it is recommended
that for at least a week after very heavy rain or heavy irriga-
tion, tangerines be spot picked for color so that they may receive
the very minimum of degreening. Because tangerine elimina-
tions are almost invariably handled at a loss (21), such spot
picking would probably pay for itself in increased pack-out, re-
gardless of the benefits from improved keeping quality.
Peel Injuries of Oranges.-Perhaps the most puzzling form
of damage associated with degreening is peel injury of oranges,
various forms of which are shown in Figure 27. This can take
many forms and is known by many names, e.g., "pitting," "stem-
end pitting," "stem-end peel breakdown," "aging," "burnt stem,"
"brown stem" and "rind staining." Despite considerable study-
ing of this subject, these authors are not prepared either to
classify these various forms of injury or to state categorically
the role played by degreening. Nevertheless, certain observa-
tions may prove helpful.
The predisposition toward peel injury starts in the grove,
although extensive checking of oranges from a wide variety of
fertilizer, spray and irrigation plots has failed to produce any
consistent correlation with particular grove treatments. Some
crops will develop peel injury almost regardless of post-harvest

Degreening of Florida Citrus Fruits

treatment, whereas others will withstand considerable abuse
without developing any peel injury other than inevitable shrivel-
ling. It is with the intermediate crops that have some predispo-
sition toward peel injury that the effect of post-harvest treat-
ments are significant.
With such crops there is a tendency for any treatment at all
to increase the amount of peel injury. The role of degreening is
indicated in Tables 15 and 16. The figures shown in Table 15
were obtained from Hamlin oranges being run in a commercial
packinghouse that still uses kerosene vapors for degreening. It
will be noted that in the fruit harvested November 1 up to 3 per-

Fig. 27.-Peel injuries on oranges. Above left: Stem-end peel break-
down on Valencia. Above right: Lateral pitting on Pineapple. Lower left:
"Brush burn" on heavily degreened Hamlin. Lower right: Stem-end peel
breakdown on Pineapple.

.207- Iov-k

Florida Agricultural Experiment Stations


S Post-
Picking Date Degreening Degreening
Treatment Treatment

Nov. 1, 1954 Kerosene
vapors Unwashed

degreened Unwashed

Kerosene Washed
vapors and waxed

Not Washed
degreened and waxed

Nov. 8, 1954 Kerosene
vapors Unwashed

degreened Unwashed

Kerosene Washed
vapors and waxed

Not Washed
degreened and waxed

*See also Figure 27 and Table 16.

Percent Stem-End
I Pitting after
Storage at 700 F. for
S1 Week 12 Weeks 3 Weeks











Degreened only ............................

Washed and polished ....-................

Washed, polished, and waxed
with a solvent wax ..................

Washed, no polishing, and
Lake Alfred 101A waxt ..........

Percent Oranges Having Peel Injury
1 Week** i 2 Weeks 1 3 Weeks

0 0 0

21 29 34

* See also Figure 27 and Table 15.
** Times are from date of picking, which was March 14, 1957.
t This refers to a fungicidal emulsion-type wax developed at the Citrus Station (53).

Degreening of Florida Citrus Fruits

cent peel injury showed up without any treatment at all. Wash-
ing and waxing without degreening raised this to 9 percent. De-
greening without washing raised peel injury to 13 percent at 3
weeks. But if the fruit from this picking was degreened, then
washed and waxed, the amount of peel injury then jumped to as
high as 58 percent. The effect of crop variability is shown by the
results with the Hamlin oranges picked a week later and handled
by this same packinghouse. The only peel injury was a mere 3
percent in the treatment that included degreening, washing
and waxing.
In most packinghouses washing and waxing also involves
polishing, since the fruit is often dried on a horsehair "polisher-
drier." If oranges are liable to develop peel injury, then de-
greening makes them particularly susceptible to damage from
the polisher brushes. With early oranges this may take the
form of lateral marking somewhat similar to "zebra skin" of
tangerines; with the Valencia variety it is more apt to show up
as stem-end pitting (Figure 27). This effect of polishing is
shown in Table 16. In this example the comparatively low level
of peel injury in the water-waxed sample is due not to the differ-
ence in the waxes but to the fact that (in accordance with com-
mercial practice) the oranges that were being treated with the
solvent wax were highly polished prior to waxing. The damage
is largely due to increased sensitivity as a result of degreening
prior to polishing. In many experiments at the Citrus Station
this form of damage could be minimized by degreening after
washing and polishing instead of before. This, however, is not
a commercial treatment as prior washing, polishing or waxing
slows or arrests degreening.
Table 17 (from Hopkins and Loucks (40)) shows how pre-
vious degreening also sensitizes the fruit (in this case Valencia
oranges) to further damage from the color-add treatment. In
fruit that had not been degreened, color-adding increased peel
injury from zero to 4.85 percent. With fruit from the same
crops that had been degreened, color-adding increased peel in-
jury from 13.25 to 35.5 percent.
The extent to which degreening brings out peel injury is
dependent not only on the use of ethylene but also on the condi-
tions within the degreening rooms. Hopkins and Loucks (40)
have reported that Valencia oranges that developed as high as
23 percent stem-end pitting when degreened under low humidity
conditions, developed only 1.5 percent stem-end pitting when de-

68 Florida Agricultural Experiment Stations

greened under high humidity conditions. Hopkins and McCor-
nack (41) have also found that air velocity (as well as humidity)
is an important factor. The higher the air velocity the more
danger of peel injury, particularly at low humidities. Moreover,
since such injured fruit are particularly vulnerable to fungal
attack, such conditions can indirectly accelerate subsequent de-
cay (41).
Hours I
from Degreened for 46 Hours Not Degreened
Replicate Treatment
when Color- Not Color- Color- Not Color-
Examined Added Added Added Added
I 114 hrs. 40.0 11.5 2.7 0.0
II 90 hrs. 31.0 15.0 7.0 I 0.0

Averages 202 hrs. 35.5 13.25 4.85 0.0

Degreening also involves a delay imposed between picking
and running the fruit through the packinghouse. Any increase
in the time between picking and washing, waxing, etc., tends
to increase subsequent peel injuries. This is illustrated in Table
18 which shows the effect of various post-harvest treatments on
Indian River Pope Summer oranges. Keeping the oranges under
moist conditions during any such delay decreases the harmful
effect upon peel injuries. Similar effects of such delays have
been reported by deFossard (11) in a very thorough study of
"brown stem" of Valencia oranges in Jamaica, and by Hopkins
and Loucks (39) and Hopkins and McCornack (41) in Florida.
Stem-End Rot.-Various workers have shown conclusively
that stem-end rot caused by Diplodia 9 is stimulated by ethylene
(4, 6, 7, 18, 24, 35, 47, 94, 96). Brooks (7) states that a de-
greening period of 42 to 45 hours caused a 9-fold increase in
stem-end rot at 2 weeks from picking. Although such results
have been found occasionally in the experiments described here,
they are hardly typical. Hopkins, Loucks and Stearns (35),
reporting results of a large number of such experiments, state
that on the average ethylene degreening increased stem-end rot
of oranges from 20.8 to 47.0 percent at 3 weeks from picking.

See footnote, page 9.

Degreening of Florida Citrus Fruits

Such results are essentially similar to those shown in Table
19 in which the effect of ethylene degreening on stem-end rot
is shown for a series of 102 experiments on 10 varieties of citrus
through three seasons. Throughout this series of experiments
the weighted averages show that degreening increased stem-end
rot at 2 weeks from picking 2.51 times. Note that the stimula-
tion of stem-end rot shown in Table 19 is due to the combination
of all factors involved in the degreening process, whereas that
shown in Table 1 is attributable solely to ethylene, since the con-
trol samples were held under normal degreening room conditions
except that ethylene was not added.

Fig. 28.-"Sloughing" on red grapefruit. Note that where finger pres-
sure has been exerted on the diseased tissue it has slipped off the sound
flesh below.

"Sloughing" of Red Grapefruit.-The term "sloughing" is
used for this disease for want of a better term. The symptoms
are quite striking (Figure 28). The outer surface of the grape-

70 Florida Agricultural Experiment Stations

fruit turns brown, soft and moist, and at the slightest pressure
separates from the sound flesh below. The trouble does not pen-
etrate through the albedo to the flesh, and eating quality is un-
affected, although the fruits are, of course, quite unsaleable.
Since this trouble appears shortly after leaving the degreen-
ing room, those instances that have come to the writers' atten-
tion have usually been blamed upon degreening. This does not
appear to be the real cause, since the occurrence of "sloughing"
seems to be related to growing conditions rather than to post-
harvest conditions (26, 28). Efforts to study and ultimately
control this disease are currently hampered by the fact that it
occurs only spasmodically (although it may cause almost total
loss of a crop when present) and disappears as suddenly as it


Percentage Losses from Peel Injury
Picking Date (1958) at 1 Week from Picking Date

February 12 -- .----... 6 21
March 3 .......................... 20 28
March 3 --------------------------------- 20 28
M arch 18 --.. ........... ............. 2 22
April 8 .. ..-.. .......... .. 2 35
April 24 .....--.....- ... .. ...................... 10 88
M ay 8 .... ................................ 2 77

A = Washed, polished, and waxed immediately on arrival at packinghouse. Stored at
70" F. in closed cartons.
B = Degreened for 48 hours in a very dry degreening room. Washed approximately
three days after picking, polished, waxed, and stored at 70 F. in closed cartons.

SBlue and Green Molds.-Although blue and green molds are
common storage diseases of citrus, the various species of the
fungus Penicillium responsible for these molds do not thrive
at temperatures much above 750 F. Due to the weakening of
these fungi by degreening room conditions, losses due to blue
and green molds are usually reduced by degreening. This is true
for various types of Florida citrus fruits and has been amply
demonstrated by Hopkins and Loucks (36).


Type of Fruit

Tangerines .............................

Hamlin Oranges ................

Valencia Oranges .............

Parson Brown Oranges .......

Pineapple Oranges .... ......

King "Oranges" ...................

T em ples ...............- .....-.........

Duncan Grapefruit ...........

Marsh Seedless Grapefruit

Foster Pink Grapefruit ........




No. of









Weighted Averages

Significant at the 1 percent level.
** Too few experiments for statistical evaluation.
t Significant at the 5 percent level (see explanatory note, Table 1).
$ Losses from stem-end rot reduced (and hence statistical significance reduced)
See also Figure 23.

Total No.
of Fruit











Average Percent Losses
from Stem-End Rot

Not Degreened Degreened

12.8 26.1

5.1 17.8

7.1 17.4

26.0 35.5

8.0 60.0

29.0 60.0

11.3 31.2

3.2 10.7

0.0 8.5
1.0 9.5

8.51 21.3

due to losses from peel injury prior to second week examination.

Increase in Analysis of
Stem-End Variance
Rot Due to "F" Values

204 60.87*

350 8.97*

245 22.32*

135 -**
750 -**

206 -**

276 7.48t, t

335 53.86*

950 -*


72 Florida Agricultural Experiment Stations

Degreening (the removal of green color by ethylene) is a
necessary process in citrus growing districts such as Florida,
where luxuriant growing conditions cause chlorophyll to persist
or reappear in the rinds of mature fruit.
The degreening process is carried out in special rooms de-
signed to treat the fruit with air containing a low (about 1:50,-
000) concentration of ethylene at controlled temperature and
Three types of degreening rooms are described: slatted-floor
rooms, solid-floor rooms (both for fruit in boxes) and degreen-
ing bins in which the fruit is handled in bulk. In all these it is
recommended that air be conditioned to approximately the fol-
lowing conditions: 85 F. dry bulb temperature, 82-830 F. wet
bulb temperature; ethylene delivery at 1 bubble per minute per
10-box capacity. Adequate air movement necessitates a fan ca-
pacity of 7.5 to 10 C.F.M. per 1-box capacity. (Here the term
"box" refers to the Florida field box of 2.232 bushels.) Ventila-
tion to prevent carbon dioxide accumulation should be either a
continual intake of approximately 2 percent of the total volume
of the room per minute, or else a complete airing twice daily.
The success of the degreening operation is dependent not only
upon packinghouse operations but also on the conditions under
which the fruit is grown. Review of the literature shows that
degreening is retarded or arrested by any factors that tend to-
ward vigorous growth, such as heavy nitrogen or potassium fer-
tilization, certain rootstocks, etc. Oil sprays and the presence
of purple scale or chaff scale also retard degreening. A crop from
a delayed or scattered bloom period is very difficult to degree.
Color break on the tree is affected by weather conditions; the
true orange color of oranges is masked by the presence of chlor-
ophyll until the the advent of cool weather, particularly cool
(below 55 F.) nights. On-tree color break of grapefruit shows
much less correlation with temperature, the changes proceeding
gradually throughout the season.
Degreening affects losses due to various post-harvest diseases
of citrus and experiments show that stem-end rot, when caused
by Diplodia, is increased considerably by degreening. Peel in-
juries of oranges and grapefruit and sloughing of red grapefruit
are also increased by degreening, although the original cause of
these troubles usually goes back to conditions prior to picking.
The epidermal injury of oranges and grapefruit usually called

Degreening of Florida Citrus Fruit

"gas burn" has been found to be caused not by ethylene directly
but by a combination of moisture and certain unidentified resi-
dues on the surface of the fruit under degreening room condi-
tions. A severe epidermal injury of Temples (and to a much
lesser extent of tangerines) has been shown to be caused by
ethylene, itself, rather than by residues or degreening room con-
ditions. Losses from Penicillium sp. (blue and green molds) are
decreased by the degreening process due to the weakening of
these fungi at temperatures above 750 F.

Acknowledgment is made to K. W. Loucks for his assistance with sta-
tistical analyses.


1. Baier, W. E., H. J. Ramsey et al. Coloring of citrus fruit. Unnum-
bered Bul. Cal. Fruit Growers Exchange. 1932.
2. Bahrt, G. M., and W. R. Roy. Progress report on the effects of no
potassium and various sources and amounts of potassium on citrus.
Fla. State Hort. Soc. 53: 26-34. 1940.
3. Bartholomew, E. T., W. S. Stewart and G. E. Carman. Some physi-
ological effects of insecticides on citrus fruits and leaves. Bot.
Gaz. 112: 501-510. 1951.
4. Bates, G. R. The development of the artificial coloration of oranges
in Southern Rhodesia and its relation to wastage. Brit. So. Africa
Co. Mazoe Citrus Expt. Sta. Pub. No. 2c. 1933.
5. Braverman, J. B. S. Citrus Products. Interscience Publishers, Inc.,
N. Y. 1949.
6. Brooks, C. Prevention of stem-end rot. Proc. Fla. State Hort. Soc.
55: 61-69. 1942.
7. Brooks, C. Stem-end rot of oranges and factors affecting its control.
Jour. Agr. Res. 68(10): 363-381. 1944.
8. Caprio, Joseph M. Regreening of Valencia oranges: temperature re-
lationships. Cal. Citrograph 40(7): 287. May, 1955.
9. Caprio, Joseph M. An analysis of the relation between regreening of
Valencia oranges and mean monthly temperatures in Southern
California. Proc. Am. Soc. Hort. Sci. 67: 222-235. 1956.
10. Clark, C. K. Coloring room studies. Ann. Rept. Fla. Agr. Expt. Sta.
1942, pp. 155-156.
11. deFossard, R. A. Progress Report: Brown stem of oranges investi-
gation. Dept. of Agr., Kingston, Jamaica. Nov. 1957.
12. Denny, F. E. Method of coloring citrus fruits. U. S. Patent (Public
Service) No. 1,475,938. Dec. 4, 1923.
13. Denny, F. E. Hastening the coloration of lemons. Jour. Agr. Res.
27: 757-769. 1924.
14. Denny, F. E. Effect of ethylene upon the respiration of lemons. Bot.
Gaz. 77: 322-329. 1924.

Degreening of Florida Citrus Fruit

"gas burn" has been found to be caused not by ethylene directly
but by a combination of moisture and certain unidentified resi-
dues on the surface of the fruit under degreening room condi-
tions. A severe epidermal injury of Temples (and to a much
lesser extent of tangerines) has been shown to be caused by
ethylene, itself, rather than by residues or degreening room con-
ditions. Losses from Penicillium sp. (blue and green molds) are
decreased by the degreening process due to the weakening of
these fungi at temperatures above 750 F.

Acknowledgment is made to K. W. Loucks for his assistance with sta-
tistical analyses.


1. Baier, W. E., H. J. Ramsey et al. Coloring of citrus fruit. Unnum-
bered Bul. Cal. Fruit Growers Exchange. 1932.
2. Bahrt, G. M., and W. R. Roy. Progress report on the effects of no
potassium and various sources and amounts of potassium on citrus.
Fla. State Hort. Soc. 53: 26-34. 1940.
3. Bartholomew, E. T., W. S. Stewart and G. E. Carman. Some physi-
ological effects of insecticides on citrus fruits and leaves. Bot.
Gaz. 112: 501-510. 1951.
4. Bates, G. R. The development of the artificial coloration of oranges
in Southern Rhodesia and its relation to wastage. Brit. So. Africa
Co. Mazoe Citrus Expt. Sta. Pub. No. 2c. 1933.
5. Braverman, J. B. S. Citrus Products. Interscience Publishers, Inc.,
N. Y. 1949.
6. Brooks, C. Prevention of stem-end rot. Proc. Fla. State Hort. Soc.
55: 61-69. 1942.
7. Brooks, C. Stem-end rot of oranges and factors affecting its control.
Jour. Agr. Res. 68(10): 363-381. 1944.
8. Caprio, Joseph M. Regreening of Valencia oranges: temperature re-
lationships. Cal. Citrograph 40(7): 287. May, 1955.
9. Caprio, Joseph M. An analysis of the relation between regreening of
Valencia oranges and mean monthly temperatures in Southern
California. Proc. Am. Soc. Hort. Sci. 67: 222-235. 1956.
10. Clark, C. K. Coloring room studies. Ann. Rept. Fla. Agr. Expt. Sta.
1942, pp. 155-156.
11. deFossard, R. A. Progress Report: Brown stem of oranges investi-
gation. Dept. of Agr., Kingston, Jamaica. Nov. 1957.
12. Denny, F. E. Method of coloring citrus fruits. U. S. Patent (Public
Service) No. 1,475,938. Dec. 4, 1923.
13. Denny, F. E. Hastening the coloration of lemons. Jour. Agr. Res.
27: 757-769. 1924.
14. Denny, F. E. Effect of ethylene upon the respiration of lemons. Bot.
Gaz. 77: 322-329. 1924.

Florida Agricultural Experiment Stations

15. Denny, F. E., and L. P. Miller. Production of ethylene by plant tis-
tues as indicated by epinastic response of the leaves. Contr. Boyce
Thompson Ins. 7(2): 97-102. 1935.
16. Deszyck, E. J., and W. Grierson. Unpublished data.
17. Florida Citrus Code of 1949 (as revised 1951, 1953 and 1955). Pub-
lished by the Florida Citrus Commission, Lakeland, Florida, as
"State of Florida Citrus Fruit Laws," November, 1957.
18. Fulton, H. R., H. E. Stevens and J. F. Wooten. Injuries and rots that
may follow the use of gasses in the coloring of Florida citrus fruits.
Proc. Fla. State Hort. Soc. 42: 184-191. 1929.
19. Grierson, W. Causes of low pack-outs in Florida packinghouses. Proc.
Fla. State Hort. Soc. 71: 166-170. 1958.
20. Grierson, W. Reducing losses in harvesting and handling tangerines.
Proc. Fla. State Hort. Soc. 69: 165-170. 1956.
21. Grierson, W. The effect of pack-out on grower profits. Proc. Fla.
State Hort. Soc. 70: 21-28. 1957.
22. Grierson, W., and W. F. Newhall. Should gassing of Temples be
banned? Citrus Magazine 16(2):30-31, 35. October, 1953.
23. Grierson, W., and W. F. Newhall. Degreening conditions for Florida
citrus. Proc. Fla. State Hort. Soc. 66: 42-46. 1953. (Reprinted
in Citrus Industry 34(12): 10-11, 15. December, 1953.)
24. Grierson, W., and W. F. Newhall. Tolerance to ethylene of various
types of citrus fruits. Proc. Am. Soc. Hort. Sci. 65: 244-250. 1955.
25. Grierson, W., and W. F. Newhall. Reducing losses in ethylene de-
greening of tangerines. Proc. Am. Soc. Hort. Sci. 67:236-243.
26. Grierson, W., and W. F. Newhall. "Sloughing"-A new disease of
red grapefruit. The Citrus Industry 36(10): 16-17. October, 1955.
27. Grierson, W., and W. F. Newhall. Degreening citrus fruits. Ann.
Rept. Fla. Agr. Expt. Sta. for 1956, pp. 186-188.
28. Grierson, W., and Roger Patrick. The sloughing disease of grapefruit.
Proc. Fla. State Hort. Soc. 69: 140-142. 1956.
29. Hall, E. G. Ethylene gas to color fruits and hasten the ripening of
tomatoes. Agr. Gaz. N. S. Wales 51:98-101, 143-145. (As quoted
by Rose, Cook and Redit, 67.)
30. Harding, P. L., J. R. Winston and D. F. Fisher. Seasonal changes in
Florida oranges. USDA Tech. Bul. 753. December, 1940.
31. Harding, P. L., and D. F. Fisher. Seasonal changes in Florida grape-
fruit. USDA Tech. Bul. 886. April, 1945.
32. Harding, P. L., and M. B. Sunday. Seasonal changes in Florida tan-
gerines. USDA Tech. Bul. 988. October, 1949.
33. Harding, P. L., and M. B. Sunday. Seasonal changes in Florida Tem-
ple oranges. USDA Tech. Bul. 1072. October, 1953.
34. Harding, P. L. Effects of oil emulsion and parathion sprays on com-
position of early oranges. Proc. Am. Soc. Hort. Sci. 61: 281-285.
35. Hopkins, E. F., K. W. Loucks and C. R. Stearns. A study of certain
methods for the control of stem-end rot and blue mold in oranges.
Proc. Fla. State Hort. Soc. 57: 87-97. 1944.

Degreening of Florida Citrus Fruit

36. Hopkins, E. F., and K. W. Loucks. A curing procedure for the reduc-
tion of blue mold decay in citrus fruits. Fla. Agr. Expt. Sta. Bul.
450. 1948.
37. Hopkins, E. F., and K. W. Loucks. Prevention of the phytotoxic action
of sodium orthophenylphenate on citrus fruits by examine. Sci-
ence 112(2920): 720-721. December 15, 1950.
38. Hopkins, E. F., and K. W. Loucks. Preservation of citrus fruits. U. S.
Patent 2,674,537. April 6, 1954.
39. Hopkins, E. F., and K. W. Loucks. Decay control research. Ann.
Rept. Fla. Agr. Expt. Sta. for 1954, p. 185.
40. Hopkins, E. F., and K. W. Loucks. Unpublished data.
41. Hopkins, E. F., and A. A. McCornack. Prevention of Rind breakdown
in organes. Citrus Mag. 21(3): 18-23, 25. November, 1958.
42. Huelin, F. E. The handling and storage of Australian oranges, man-
darins, and grapefruit. Council for Sci. and Ind. Res. (Australia)
Bul. 154. 1942.
43. Hume, H. H. The cultivation of citrus fruits. Macmillan. 1926.
44. Juritz, Chas. F. Chemical investigations in regard to citrus. Union
of South Africa. Dept. of Agr. Sci. Bul. No. 40. 1925.
45. Kaltenbach, D. The artificial ripening of fruit by acetylene. Bul. Int.
Inst. Refrig. 20: 214. 1939. Abst. in Hort. Abst. 9(4): 1471. 1939.
46. Klotz, L. J., et al. Water spot of Navel oranges. Studies of the prob-
lem to 1948. Calif. Agr. Expt. Sta. Unnumbered, undated leaflet.
47. Loucks, K. W., and E. F. Hopkins. A study of the occurrence of
Phomopsis and Diplodia rots in Florida oranges under various con-
ditions and treatments. Phytopath. XXXVI(9): 750-757. Septem-
ber, 1946.
48. Lynch, L. J. A suggested co-enzyme hypothesis for the ripening of
fruits by ethylene gas treatment. Proc. Roy. Soc. of Queensland
47(3):18-24; 1935. 1936.
49. Martin, W. E. Physiological studies of yield, quality and maturity
of Marsh grapefruit in Arizona. Ariz. Agr. Expt. Sta. Tech. Bul.
97. 1942.
50. Mediterranean Fruit Fly Program. USDA cooperating with the
Florida State Plant Board, Memorandum No. 15, August 13, 1958.
51. Merck, Index, The. Sixth Ed. Merck and Co., Inc., Rahway, N. J.
52. Munsell Book of Color. Munsell Color Co., Inc., 10 East Franklin St.,
Baltimore 2, Maryland.
53. Newhall, W. F., and W. Grierson. A low cost, self-polishing, fungi-
cidal water-wax for citrus fruits. Proc. Am. Soc. Hort. Sci. 66:
146-154. 1955.
54. Nixon, H. W. Lemons: Picking, washing, grading, packing. Calif.
Citrog. 25: 101. 1940.
55. Phillips, R. V., and W. Grierson. Cost advantages of bulk handling
through the packinghouse. Proc. Fla. State Hort. Soc. 70: 171-177.
56. Powell, H. C., and I. Matthew. Ethylene colouring of citrus fruits.
Univ. of Pretoria (Union of S. Africa) Agr. Bul. Ser. 1(25):1-20.

Florida Agricultural Experiment Stations

57. Prosser, D. S., W. Grierson, Eric Thor, W. F. Newhall, and J. K.
Samuels. Bulk handling of fresh citrus fruit. Fla. Agr. Expt.
Sta. Bul. 564. June, 1955.
58. Rebour, H., Le Deverdissage des Agrumes: Comment tirer parti, en
algerie de de l'experience floridienne. Direction de L'Agriculture,
Service Agricole General, Service de l'Aboriculture, Government
General de 1'Algerie.
59. Regulations: Pursuant to the Florida Citrus Code. Florida Citrus
Commission. August 1, 1957.
60. Reitz, H. J. Timing fertilization of citrus in the Indian River area.
Citrus Mag. 19(5): 8, 14, 18. January, 1957.
61. Reuther, W., and P. Smith. Fertilization and quality of oranges.
Citrus Mag. 15(2):31-34. October, 1952.
62. Reuther, W., and P. Smith. Relation of nitrogen, potassium, and mag-
nesium fertilization to some fruit qualities of Valencia orange.
Proc. Am. Soc. Hort. Sci. 59: 1-12. 1952.
63. Reuther, W., and P. Smith. Effect of method of timing nitrogen fer-
tilization on yield and quality of oranges. Proc. Fla. State Hort.
Soc. 67: 20-26. 1954. (Repr. in Citrus Industry 36(3): 5-7, 12-13,
19. March, 1955.)
64. Riehl, L. A., and G. E. Carman. Water spot on Navel oranges: Only
slight injury observed in orchards treated with parathion for Cali-
fornia red scale control. Calif. Agr. 7(10): 7-8. October, 1953.
65. Rohbaugh, P. W. Measurement of small concentrations of ethylene
and automobile exhaust gases and their relation to lemon storage.
Plant Phys. 18(1): 79-89. 1943.
66. Rose, D. H., C. Brooks, C. O. Bratley, and J. R. Winston. Market
diseases of fruits and vegetables: Citrus and other subtropical
fruits. USDA Misc. Pub. 498. June, 1943.
67. Rose, D. H., H. T. Cook, and W. H. Redit. Harvesting, handling and
transportation of citrus fruits. USDA Bibl. Bul. No. 13. January,
68. Rouse, A. H., and J. C. Bowers. Packinghouse research. Citrus Expt.
Sta., Lake Alfred, Fla. Progress Report. June 30, 1950.
69. Roy, W. R. Effect of potassium deficiency and of potassium derived
from different sources on the composition of the juice of Valencia
oranges. Jour. Agr. Res. 70(5): 143-169. 1945.
70. Sievers, A. F., and R. H. True. A preliminary study of the forced cur-
ing of lemons as practiced in California. USDA Bur. of Plant Ind.
Bul. 232. 1912.
71. Sinclair, W. B., E. T. Bartholomew and W. Ebeling. Comparative
effects of oil spray and hydrocyanic acid fumigation on the compo-
sition of orange fruits. Jour. Econ. Ent. 34: 821-829. 1941.
72. Sites, J. W., and W. L. Thompson. Timing of oil sprays as related
to fruit quality, scale control, coloring and tree condition. The
Citrus Industry 29(4): 5-9, 26. 1948.
73. Sites, J. W., W. L. Thompson and H. J. Reitz. A comparison of para-
thion and oil sprays in regard to their effect on the internal quality
of citrus fruit. Citrus Mag. 12(8): 30-33. 1950.

Degreening of Florida Citrus Fruit

74. Sites, J. W., and H. J. Reitz. The variation in individual Valencia
oranges from different locations of the tree as a guide to sampling
methods and spot-picking for quality. Proc. Am. Soc. for Hort.
Sci. 54: 1-10, 1949; 55: 73-80, 1950; 56: 103-110, 1950.
75. Sites, J. W., H. J. Reitz and E. J. Deszyck. Some results of irrigation
research with Florida citrus. Proc. Fla. State Hort. Soc. 64: 71-79.
76. Snedecor, G. W. Statistical methods. Iowa State College Press.
77. Stearns, C. R., Jr. Color break studies. Fla. Agr. Expt. Sta. Ann.
Rept. for 1942, pp. 156-157.
78. Stearns, C. R., Jr., and Geo. T. Young. The relation of climatic con-
ditions to color development in citrus fruit. Proc. Fla. State Hort.
Soc. 55: 59-61. 1942.
79. Stevenson, C. D. Artificial colouring and ripening of fruits. Queens-
land Agric. Jour. (Australia) 78(3): 151-155. March, 1954.
80. Stofberg, F. J., and E. E. Anderssen. Effets of oil sprays on the yield
and quality of Navel and Valencia oranges. Union So. Africa,
Dept. Agr. Sci. Bul. 296. 1949.
81. Taylor, O. C., G. E. Carman, R. M. Burns, P. W. Moore and E. M.
Nauer. Effect of oil and parathion sprays on orange size and
quality. Cal. Citrog. 41(12): 452-454. October, 1956.
82. Taylor, O. C., G. E. Carman, R. M. Burns, P. W. Moore, and E. M.
Nauer. Size and quality of oranges as affected by oil and para-
thion sprays. Citrus Leaves 36(11): 10-11. November, 1956.
83. Thompson, W. L. Some problems of control of scale insects on citrus.
Proc. Fla. State Hort. Soc. 55: 51-59. 1942.
84. Thompson, W. L., and E. J. Deszyck. Phosphatic insecticides mixed
with oil emulsion for scale control and their effect upon fruit qual-
ity. Citrus Industry 39(3): 7-8, 28-29. March, 1958.
85. Thompson, W. L., J. T. Griffiths and J. W. Sites. A comparison of oil
emulsion and parathion for the control of scale insects on citrus.
Proc. Fla. State Hort. Soc. 64: 66-71. 1951.
86. Thompson, W. L., J. T. Griffiths and J. W. Sites. A comparison of
oil emulsion and parathion for the control of scale insects on citrus.
Citrus Mag. 14(9): 24-27. May, 1952.
87. Thompson, W. L., R. M. Pratt and R. B. Johnson. Citrus insect con-
trol. Citrus Industry 35(11): 3, 17. November, 1954.
88. Tomkins, R. G. Unsolved problems in the preservation of food: The
influence of cultural conditions on the quality and preservation of
fruits and vegetables. Jour. Sci. Food Agr. 5: 161-167. 1954.
89. Thullbery, Howard A. Irrigation practices. Citrus Mag. 19(5): 29.
January, 1957.
90. Turnbull, James. Determining effect of different quantities of irriga-
tion water on quantity of fruit produced. Fla. Agr. Expt. Sta. Ann.
Rept. for 1949, pp. 317-321.
91. U. S. Standards for Florida Grapefruit: (17 F.R. 7408) 9/14/52. Pro-
duction and Marketing Administration, USDA, Washington, D. C.
92. U. S. Standards for Florida Oranges and Tangelos (20 F.R. 7205)
10/14/55. Production and Marketing Administration, USDA,
Washington, D. C.

Florida Agricultural Experiment Stations

93. U. S. Standards for Florida Tangerines (20 F.R. 5845) 9/12/55. Pro-
duction and Marketing Administration, USDA, Washington, D. C.
94. Wardlaw, C. D. Tropical fruits and vegetables: Their storage and
transport. Trop. Agr. XIV(5): 131-139 and (6): 163-170. 1937.
95. Winston, J. R., and J. M. Lutz. Recent developments in citrus color-
ing. Jour. Agr. Res. 28: 45-48. 1931.
96. Winston, J. R. Preparation and packing of oranges for shipment.
Ind. and Eng. Chem. XXVI(7): 762-765. 1934.
97. Winston, J. R., and R. W. Tilden. The coloring or degreening of ma-
ture citrus fruits with ethylene. USDA, unnumbered multilith,
September, 1932. Rev. July, 1935.
98. Winston, J. R. Degreening of oranges affected by oil sprays. Proc.
Fla. State Hort. Soc. 55: 42-45. 1942.
99. Winston, J. R. Harvesting and handling citrus fruits in the Gulf
States. USDA Farmers Bul. 1763. Rev. 1950.
100. Winston, J. R. The coloring or degreening of mature citrus fruits
with ethylene. USDA Circ. 961. May, 1955.
101. Yost, G. E., E. K. Bowman, W. Grierson and F. W. Hayward. De-
greening citrus fruits in large pallet boxes. Citrus Magazine
21(9): 10-11. May, 1959.
102. Others, W. W., and 0. C. McBride. The effect of oil sprays on the
maturity of citrus fruits. Proc. Fla. State Hort. Soc. 42: 193-218.


Acetylene, 8
Adjustable air intake, 44-46
Air circulation. 16, 43-44, 68, 72
Air velocity, 68
Air conditioning, 7
Arsenic, 56
Australia, 7, 59
Bahrt and Roy, 54
Baier and Ramsey, 8, 43
Bean, E. H., 7
Bloom, 55
"Blotching", 59
Blue mold, 7, 70, 73
Box, capacity, 39, 72
Brooks, 68
Brush burn, 65
Bulk degreening bins, 3, 27-30
Bulk handling, 3, 27-30, 45-46
California, 11, 13, 51, 58
California Navels, 47
Canvas curtains, 31-35, 44
Caprio, 56
Carbon dioxide, 13, 32, 45-46
Carotenoid pigments, 5
Ceilings, 27
Chaff scale, 51
Chlorophyll, 5, 72
Clamp trucks, 15, 32, 34
Climatic conditions, 5, 42, 53, 55
Color-added, 5

Color break, 55
Colorimeter, 8
Condensation on fruit, 12
Condensation on walls, 31
Control sample, 8
Construction of rooms, 31-37
Cooling by refrigeration, 43
Cost of ethylene, 39
Cultural factors, 47-56
Curing, 7
Curtains, 31-35, 44

Decay, 6, 12
deFossard, 68
Degreening cabinets, 8
Degreening room construction, 31-37
Degreening room floors, 18, 23, 34-37
Degreening room temperature, 14-16
Degreening room operation, 37-47
Denny, 6, 7, 8
Deszyck, 49, 54
Diplodia natalensis, 9, 68, 72
Doors, 34, 36
Double ceiling, 26-27
Dowicide-hexamine, 30
Dry bulb temperature, 14-16, 27,
42-43, 72
Drying fruit, 41-42
Ducts, 24-25
Duncan grapefruit, 10, 11, 16, 17, 30,
31, 47, 48, 55, 71

Degreening of Florida Citrus Fruit

Early fruit, 6
Eliminations, 6
Enzymes, 14
Ethylene, 5. 8-10, 13, 37-41
"Ethylene burn", 12-13
Ethylene composition, 8
Ethylene cost, 39
Ethylene concentrations, 9, 39-41, 61
Ethylene delivery, 9, 37-41
Ethylene injury, 12-13, 56-61
Excelsior grapefruit, 49
Experimental results, 7
Explosion hazard, 9

False ceiling, 26-27
Fans, 20. 21, 22, 26, 41, 43, 72
Fertilizers, 52-55, 64
Floor, 18, 23, 34-37
Floor chain motor, 37
Florida red scale, 52
Flow meter, 39
Foster Pink, 10, 30, 71
F. M. C. room, 19, 23
Fruit fly, 44
Fumigation, 44
Fungicides, 30, 67-68

Gas analyses, 45-46
"Gas burn", 16, 56-61, 73
Green spots, 14, 51
Grades, 6, 52, 53
Grapefruit, 8, 11, 16, 17, 56, 72
Griffiths, 54
Grove practices, 47-56
Growing conditions, 47-56

Hale rooms, 18-19, 20
Hamlin oranges, 5, 10, 16, 17, 30, 31,
47, 48, 56. 58, 65, 66, 71
Hand trucks, 15, 32, 34
Handling damage of tangerines,
Hardening-off, 47, 50
Harding, 55
History, 7
Hopkins and Loucks, 67-68, 70
Hopkins and McCornack. 68
Humidity, 10-13, 41-42, 58-59, 68

Immature fruit, 58
Indian River, 52, 53
Injuries (degreening), 56-71
Irrigation, 54-55, 64

Jamaica, 68
Johnson, 52
Juice content, 6
Juritz, 56

Kerosene fumes, 7, 8, 37, 41, 65, 66
Kerosene stoves, 7, 40
King "oranges", 71

Late bloom, 55
Laws, 6, 15
Legal standard (maturity), 6
Lemons, 51
Lue Gim Gong, 5
Malathion, 50
Manometer tube, 38
March grapefruit, 16, 30, 54, 55, 71
Martin, 54
Maturity, legal standards, 6
Mechanical injury, 14
Metering orifice, 37, 38
Mezzanine floors, 34
Mineral oil, 37
Minor elements, 54
Munsell color scale, 8
Navel oranges, 47, 51, 59
Night temperatures, 5
Nitrogen, 14, 52, 53, 72
Off bloom fruit, 55
Oil spotting, 14
Oil sprays, 49, 72
Oleocellosis, 14
Operation of degreening rooms,
Organic volatiles, 13
Overloading, 23
Oxygen, 13
Packout, 6, 55
Parathion, 49
Parson Brown oranges, 5, 30, 54, 71
Peel injury, 12, 14, 41, 42, 60, 64-68,
Peel oil, 14
Penicillintm, 70, 73
Phomopsis citri, 9
Phosphate, 52
Pineapple oranges, 65, 71
Pitting, 47, 50, 65-68
Plant narcotics, 13
Plenum area, 19, 23
Polisher-driers, 30, 61
Pope Summer oranges, 5, 70
Potassium, 52, 72
Power trucks, 25, 31, 36, 37
Precipitation of moisture, 12
Pregrading, 30
Presorting, 30
Pretreatments, 30
Prewashing, 30
Prices, 6, 55
Production methods, 47-56
Profits, 6
Purple scale, 51-52
Quailing, 7
Radiator, 14, 41
Ratio, 6
Red grapefruit, 69-70

Florida Agricultural Experiment Stations

Refrigeration, 43
Regreening, 52
Re-running waxed fruit, 30-31
Regulation of degreening rooms,
Reitz, 52, 53, 54, 55
Relative humidity, 10-13, 41-42,
58-59, 68
Respiration, 13
Reuther and Smith, 52
"Ring burns", 57
Rootstock, 55
Rose et al., 13, 57
Rots, 6, 12
Ruby Red, 30

Scale insects, 51-52
Self-polishing fungicidal wax, 66
"Set back" space, 32
"Shot" method of delivering ethyl-
ene, 9
Shrinkage, 13
Shrivelling, 10, 13, 41
Sievers and True, 7
Silver cluster grapefruit, 55
Sites, 49, 55
Slatted floor rooms, 18-23
"Sloughing" of red grapefruit, 69-70
Smoke gun, 23
"Smoke house", 40
Snedecor, 8
Soap, 30
Solid floor rooms, 23, 25-27
"Solids", 51, 54
South African oranges, 13, 56
Spot picking, 6
Spray program, 49-52, 64, 72
Spray residues, 12, 73
Stacking, 23
Statistical significance, 10, 11
Steam nozzles, 42
Stearns, 55, 68

Stem-end "aging", 65-68
Stem-end rot, 9, 68-71
Stevenson, 59
Sweating, 5, 7

Tangerines, 8, 10, 57, 61-64, 71, 73
Temperature, 8, 14-16, 42, 58
Temperature control, 42-43
Temples, 10, 57, 60-61, 71, 73
Tent degreening rooms, 34-35
Thermostat, 24-25, 26
Thompson, 49, 50, 51
Timing of fertilizers, 54
Tompkins, 52
Trace element nutrition, 54
"Trickle" method, 9, 37-39
Turnbull, 55

U.S.D.A., 5
Vacuum area, 19, 27
Valencia oranges, 5, 10, 47, 48, 51,
52, 53, 56, 66, 67, 71
Ventilation, 16-18, 44-47
Volatiles, 13, 17
Wall construction, 31-32
Washing, 30, 66
Waste gases, 16-18
Water column, 38
"Water spotting", 51
Water spray, 41
Water vapor, 10
Waxing, 30-31, 66-67
Weather, 5, 42, 53, 55
West Indies, 7
Wet bulb temperature, 41-42, 72
Wet fruit, 10, 41
Winston, 30, 44, 49, 52
Others, 49
"Zebra skin", 64

University of Florida Home Page
© 2004 - 2010 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated October 10, 2010 - - mvs