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Group Title: Circular
Title: Postharvest handling of Florida blueberries
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 Material Information
Title: Postharvest handling of Florida blueberries
Series Title: Circular
Physical Description: 8 p. : ill. ; 28 cm.
Language: English
Creator: Talbot, Michael T ( Michael Thomas ), 1948-
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1992
 Subjects
Subject: Blueberries -- Handling -- Florida   ( lcsh )
Blueberries -- Postharvest technology -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
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Bibliography: Includes bibliographical references (p. 8).
Statement of Responsibility: M.T. Talbot ... et al.
General Note: Title from cover.
General Note: "May 1992."
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Bibliographic ID: UF00014450
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA6907
ltuf - AJG5666
oclc - 26846478
alephbibnum - 001752709

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0992
C 1992


Postharvest Handling

of Florida Blueberries

M. T. Talbot, T. E. Crocker, P. M. Lyrene, and J. P. Emond


























Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida
John T. Woeste, Dean


Circular 1050


I













































































M.T. Talbot, Associate Professor, Agricultural Engineering Department, T.E. Crocker, P.M. Lyrene, Professors, Fruit Crops
Department, and J.P. Emond, Graduate Assistant, Agricultural Engineering Department.








Introduction
Blueberries are one of the most delicate and
highly perishable fruits. Their climacteric physi-
ological characteristics allow them to be harvested
in a "just ripe" condition. The quality of fresh blue-
berries depends on their maturity and appearance
(color, fruit size, freedom from defects and decay),
firmness, and flavor (determined by amounts of
sugars, organic acids, phenolics, and characteristic
aromatic volatiles). The principal decay likely to
affect blueberries during postharvest are gray mold
(Botrytis rot), Anthracnose, and Alternaria rot.
Even a small amount of infestation can quickly
spread throughout an entire package.

The most important factors in attaining and
maintaining good quality are harvesting at the
"just ripe" stage, avoiding physical injuries during
all handling steps, enforcing strict quality control
procedures, prompt precooling, and providing
proper temperature and relative humidity during
transport and handling at destination.

Loss of quality, results in blueberries which are
not acceptable to consumers. Quality decreases
rapidly at ambient temperatures, therefore, proper
temperature management is important in main-
taining blueberry quality. Proper temperature
management of blueberries begins with proper
precooling (rapid removal of field heat) from field
temperatures which can be higher than 300C
(860F). Rapid removal of field heat is critical to
retard deterioration of blueberries. For maximum
quality retention, blueberries should be precooled
to near -0.5 to 0C (31 to 320F) within 1 hour of
harvest and maintained at -0.5 to 0C (31 to 320F)
and 90 to 95% relative humidity throughout the
marketing channels [71.1 For commercial blue-
berry operations in Florida, this ideal is rarely
achieved. The level of precooling achieved with
Florida blueberries depends on various factors, in-
cluding volume of blueberries handled, cooling and
handling equipment availability and capability,
economics, energy, and market conditions.

Blueberries are an important crop in the United
States. Nationally, Florida follows Michigan, New
Jersey, North Carolina, Georgia, Washington, and
Oregon in fresh blueberries production with an av-
erage annual value of $5 million for the last 5 years
[3]. During the past 5 years, blueberry yields in
Florida averaged about 3,000 pounds per acre with
6 million pounds packed off2.1 thousand acres.
Yields per acre should increase as the acreage


matures. Prices for fresh blueberries averaged over
$4.00 per pound between April 1 and May 20 (due
to a favorable world market window). This
normally falls to $1.00 per pound after June 1.

Blueberry growers and packers in Florida are
aware of the value of their crop and of the quality
demands of consumers. Improvements in tempera-
ture management will allow them to produce
higher quality blueberries. Most blueberries in
Florida are room cooled although some operations
use forced-air cooling (including evaporative cool-
ing) in fiberboard flats stacked on pallets. Room
cooling of blueberries is not an acceptable precool-
ing method nor is reliance on refrigerated trucks
during transit.

This publication presents quality parameters,
handling and cooling requirements, cooling meth-
ods, and management guidelines for maintaining
the quality of Florida blueberries. Studies
conducted to establish the relationship between
condensation and container design and the effects
of new container designs on cooling rates of blue-
berries are discussed. Management guidelines or
recommendations to the packinghouse operators
concerning possible system performance
improvements are presented, such as increasing
resident time within the forced-air precooler to
achieve better cooling or lowering the cold room
temperature to prevent warming ofprecooled
blueberries.

Quality parameters
The United States grade standards for blue-
berries are based on the following quality factors;
maturity, color, size, and freedom from defect and
decay [8]. Florida shippers might not use U.S.
grades for shipping, but these, or similar grades,
are used for inspection purposes at destination.
Therefore, all growers should be aware of the grade
specifications. If the blueberries do not meet the
grade standards when they are picked, it is impos-
sible for them to make grade at destination. For
hand-harvested operations, it is important that a
system be developed by which each container of
fruit harvested is inspected and weighed in the
field to make sure it meets quality standards before
the picker is credited. For machine-harvested
operations, it is important that immature and
overmature berries, damaged berries and trash be
eliminated on the sorting line.

'Numbers in brackets refer to cited references








U.S. #1 grade blueberries must be of one variety
or with similar varietal characteristics with small
dry stem scars, which are firm, not overripe or un-
developed, and which are free from mold or decay
and free from damage caused by dirt, moisture, for-
eign matter, disease, insects, mechanical or other
means. Each blueberry should be blue in color
with a minimum diameter of 10 mm (7/16 inch) [5].
Other suggested quality attributes include pH (2.25
to 4.25), citric acid (0.3 to 1.3%), soluble solids
(greater than 10%), soluble solids to acid ratio (10
to 33) and firmness (greater than 7 grams for 0.01
cm on Instron testing machine) [5].

Moisture loss from the blueberry fruit causes
weight loss and shriveling and must be minimized.
The whitish waxy covering on the fruit (bloom) is
important, both for its effect on the color of the fruit
and in preventing moisture loss through the fruit
skins. Postharvest steps which removed the bloom
should also be avoided [13].

Cooling requirements
Understanding the cooling requirements of horti-
cultural commodities requires knowledge of their
biological responses. Fresh horticultural crops are
alive and carry on many biological processes essen-
tial to the maintenance of life. They must remain
alive and healthy until processed or consumed.
Energy that is needed for these life processes comes
from the food reserves that accumulated while the
commodities were still attached to the plant [8].

Respiration is the process by which food reserves
are converted to energy. Through a complex se-
quence of steps, stored food (sugars and starches)
are converted to organic acids and subsequently to
simple carbon compounds. Oxygen from the sur-
rounding air is used in the process while carbon di-
oxide is released. Some of the energy of respiration
is used to maintain the life processes and some is
released in the form of heat, called "vital heat".
Removal of this heat must be considered in the
temperature management program.

The respiration rate varies with commodity,
variety, ripeness, injuries, temperature, and other
stress related factors. Blueberries have a moderate
respiration rate, 2-10 mg CO/kg-h (440-2,200 Btu
per ton per day) at 0C (320F) [7]. The major factor
affecting respiration rate is the product tempera-
ture. Since the final result of respiration activity is
productdeterioration and senescence, achieving as
low a respiration rate as possible is desirable. For
each 100C (180F) temperature decreases respiration


activity decreases by a factor of 2 to 4 [3]. For ex-
ample the respiration of blueberries at 100C (500F)
is 23-35 mg CO/kg-h (5,100-7,700 Btu per ton per
day), over 4 times greater than at 0C (320F).
Therefore blueberries must be rapidly precooled to
slow their metabolism (physiological deterioration)
to maximize quality and storage life for shipping
and handling operations.

Blueberries are not a chilling sensitive crop
(crops which must be stored at temperatures gener-
ally above 100C (500F) to prevent physiological
damage). Therefore, they can be safely cooled to a
temperature of-0.5 to 0C (31 to 320F) and should
be maintained at that temperature throughout the
marketing channels. The required rate of cooling
during precooling can be expressed in terms of the
half cooling time or the 7/8 cooling time (Figure 1).
These values remain constant for the particular
set of precooling conditions from which they were
determined. The half cooling time is the time
required to remove one half of the temperature dif-
ference between the initial pulp temperature and
the cooling medium temperature. For commercial
precooling, it is recommended [14] that 7/8 of the
difference between the pulp temperature and the
cooling medium temperature be removed prior to
storage and transport. Under ideal circumstances
the 7/8 cooling time is equal to about three times
the amount of the half cooling time.

For example, if blueberries are harvested at
30C (860F) and cooled in a forced-air cooler with
an air temperature of 1.1C (340F) the half cooling
time would be the time required to remove 14.5C
(260F)3 or for the blueberries to cool to 15.5C
(600F)'. For the same situation, the 7/8 cooling


25-

o
20-

s 15-
-.4
S 10.

5


Initial Product Temperature


Curve of Average Produce Temperature

- A g P 1/2 Cool

C_ 3/4 Cool
I I 7/8 Cool
-----1-"----!---^- ---_
Room Air Tenmperature II
S1 2 3 4


NUMBER OF HALF-COOLING TIMES ELAPSED
Figure 1. Cooling curve showing the drop In temperature from
the Initial product temperature through one (112
cool), two (3/4 cool), and three (7/8) cool half-cooling
times.








time would be the time required to remove 25.3C
(45.50F)5 or for the blueberries to cool to 4.7C
(40.50F)6. By developing a precooling schedule [14]
the 7/8 cooling time could be established. Therefore
after precooling for a time period equal to the 7/8
cooling time or by determining that the pulp tem-
perature was 4.70C (40.50F), the blueberries would
be removed from the precooler and moved to cold
storage for additional cooling to o0C (320F).

Cooling schedules should be utilized to maximize
efficiency. Use of a schedule allows cooling times to
be adjusted based on the initial temperature of the
berries. Blueberries coming from the field at
18.3C (650F) need less time in the precooler than
fruits arriving at 32.20C (900F). Leaving blueber-
ries in the forced-air cooler longer than necessary
can lead to undesirable water loss because of rapid
air movement. On the other hand, inadequate
cooling can lead to rapid deterioration due to high
temperatures.

Cooling methods
The selection of a particular precooling method is
determined by several factors including: the rate of
cooling required, compatibility of the method with
the commodities to be cooled, subsequent storage
and shipping conditions, and equipment and
operating costs.

During precooling, the sensible heat (or field
heat) from the product is transferred to the ambi-
ent air. The rate of heat transfer, or cooling rate, is
critical for the efficient removal of field heat and
depends on three factors: time, temperature, and
contact. In order to achieve maximum cooling, the
product must remain in the precooler for sufficient
time to remove the heat (7/8 cooling time). This is
particularly important during busy periods when it
may be tempting to "push" product through the
precooler. A correctly sized precooler should have
sufficient capacity so as to provide adequate resi-
dent time for precooling, while at the same time
not slowing subsequent packing and/or handling
operations. The cooling medium (air) must be
maintained at a constant temperature throughout
the cooling period. If the refrigeration system is
undersized for the capacity of product requiring
precooling, the temperature of the medium will
increase over time. The cooling medium must also


s [30 1.1] 1/2 = 14.5C
[30 14.5]= 15.5C
S[30 1.1] 7/8 = 25.3C
S[30 25.3] = 4.70C


([86 34] 1/2 =260F)
([86 26] = 60F)
([86 34] 7/8 = 45.5F)
([86 45.5] = 40.50F)


have intimate contact with the surfaces of the blue-
berry. Inappropriately designed containers can
markedly reduce flow of the cooling medium.

The rate of cooling depends not only on time,
temperature, and contact with the commodity, but
also on the cooling method employed. As noted
above, most blueberries in Florida are room-cooled
with some forced-air cooling. Hydrocooling (shower-
ing or immersion in chilled water) is not recom-
mended because wet berries are much more suscep-
tible to decay. Cooling with crushed or slush ice is
even worse because the berries are likely to sustain
physical damage. Vacuum cooling would produce
critical moisture loss and procedures using water
spray could not be used. Again, room cooling of
blueberries is not an acceptable precooling method
because it is too slow nor is reliance on refrigerated
trucks during transit.

Forced-air cooling (pressure cooling)
Forced-air cooling, which has been described in
detail in various publications [1, 2, 6, 8, 12, 14], can
solve many difficult cooling problems because it
provides for cold air movement through, rather
than around, containers. The system, which cre-
ates a slight pressure gradient to cause air to flow
through container vents, achieves rapid cooling as a
result of the direct contact between cold air and
warm product. With proper design, fast, uniform
cooling can be achieved through unitized pallet
loads of containers. Various cooler designs can be
used, depending on specific needs. Existing cooling
facilities can often be converted to forced-air cool-
ing, provided sufficient refrigeration capacity and
cooling surfaces (evaporator coils) are available.
Some variations in forced-air cooler design are
described here.

Forced-air tunnel
This is the traditional forced-air cooling system.
Essentially, two rows of palletized containers or
bins are placed on either side of an exhaust fan
leaving an aisle between rows. The aisle and the
open end are then covered to create an air
plenum tunnel (Figure 2). With the exhaust fan
operating, a slight negative air pressure is created
within the plenum tunnel. Cold air from the room
then moves through any openings in or between
containers toward the low pressure zone (the tun-
nel), cooling the product as it moves. The exhaust
fan can be a portable unit that is placed to direct
the warm exhaust air toward the air return of the
cold room, or it can be a permanent unit which




























Figure 2. Forced-air tunnel with portable exhaust fan.

also circulates the air over the cooling surface and
returns it to the cold room (Figure 3).

Cold wall
This is a permanently constructed air plenum
equipped with an exhaust fan. It is often located at
one end or side of a cold room, with the exhaust fan
designed to move air over the cooling surface.
Openings are located along the room side of the
plenum against which stacks on pallet loads of
containers can be placed. Various damper designs
have been developed so that air flow is blocked
except when a pallet is in place. Each pallet will
start cooling as soon as it is in place; thus there is
no need to await deliveries to complete a tunnel.
Shelves are often built so that multi-layers of
pallets can be cooled with this system. Different


Figure 3. Forced-air cooler with permanent constructed air
plenum.


packages, and even partial pallets, can be accom-
modated by proper design of the damper system.
This is a benefit in some operations where a range
of commodities or varieties is handled. Each pallet
must be promptly moved from the cooler as soon as
it is cooled in order to avoid unnecessary desicca-
tion from continued rapid air flow over the product.

The usual design air flow rate for blueberry
cooling is 2.1x103 m3/s per kg (2 ft3/min per Ib) of
fruit with the air temperature at -0.5 to o0C (31 to
320F) [8]. The cooling time varies from 1.5 to 2.5
hours depending on initial temperature of the fruit.
In practice, air flow rate generally varies from
1.0x10-3 to 4.2x103 m3/s per kg (1 to 4 ft3/min
per lb) of fruit.

Blueberries are usually precooled at the packing-
house in pallets consisting of 96 open-top fiber-
board, single-layer tray cartons containing 12 200
or 400 gram (1/2 or 1-pint) containers, weighing
approximately 454 kg (1,000 pounds). The pallet is
usually 3 cartons deep, 2 cartons wide, and 16
cartons high. Most boxes are constructed in such a
manner that tray cartons are connected together
with wires and each carton is connected to the car-
ton below with tabs protruding up into the carton
above for load stability. The cartons have enough
open area to allow for passage of cooling air. Cold
air is forced through the pallet and recycled
through a refrigeration unit.

Fresh market packaging
A considerable amount of information is avail-
able on the effect of package type on blueberries [4,
5, 6, 10, 11]. All of these studies have shown the
importance of a good packaging system maintain-
ing the quality of blueberries. The traditional
molded pint pulp carton covered with cellophane
wrap is being replaced by new packages which lend
themselves to mechanized forming, filling, and clos-
ing, are easy to handle and transport, are attractive
and convenient to the consumer, increase shelf life,
and reduce water loss. New flat-top containers
(Figure 4) have shown a high degree of approval
and acceptance by marketers and consumers.
These containers eliminate the 20% overfill
normally associated with the traditional pulp con-
tainers to compensate for their high rate of water
loss. New film wrappings are being developed
which are superior to cellophane overwrap in terms
of reduced moisture loss, decay and condensation.

Effective carton venting is essential for forced-air
cooling to work efficiently. Cold air must be able to

























0.09 m
Figure 4. Experimental 220 g package for fresh blueberries.

pass through all parts of a carton. For this to hap-
pen, carton vents must remain open after stacking.
Thus, venting patterns are important. Too little
venting will restrict air flow; too much venting will
weaken the carton.

The standard blueberry carton has a vent hole
that looks like a channel with sloping sides cut in
the upper fourth of two opposite sides of the carton
(Figure 5). The opening represents 14% of the side
of carton. When the air is forced through the vent
hole, it passes through the gap between the top of
the blueberry containers and the bottom of the
carton immediately above, thus cooling the fruit
from the top of the container.

Cooling research for strawberries [1], has estab-
lished the relationship between cooling rate and air
flow rate which should be adequate for blueberries.
This study [11 indicates a large increase in cooling
rate when the air flow rate was increased from
1.0x10-3 to 2.1x103 m3/(kg s) (1.0 to 2.0 ft3/min Ib)
and a relatively small increase at higher flow rates.


Figure 5. Blueberry containers In tray carton.


Cooling time was also shown to be a function of
location of the fruit in the carton with respect to the
entering air [6]. The more down-stream the loca-
tion, the longer the cooling time Figure 5. Figure 6
shows the effect of fruit location on cooling time at
various air flow rates for the traditional container
while Figure 7 indicates the more uniform cooling
of an experimental flat-top container with a perfo-
rated cover. The new container allowed blueberries
to be cooled up to 20% faster than the traditional
container.

When cooling pallets three cartons in depth, the
last container in the inside carton can take approxi-
mately twice as long to reach 7/8 cooling as the first
container in the outside carton. This is known as
the bed effect in terms of the temperature gradient
along the flow path at the time the first container
achieved 7/8 cooling. A temperature gradient of 5

25-




20.


E 10 1 2 3

7/8 coong tlme

room---

o0 O 1o 10 200 2
Time (mn)
Figure 6. Temperature versus time during precooling for
standard pulp container [6].

25

20.


E 15
SO !


Figure 7. Temperature versus time during precooling for
experimental performated flat-top container [6].








to 60C (9 to 10.80F) can exists between the first
(coldest) container and the last (hottest) container.
In some packinghouses, the operators use the fruit
on top of the first container to gauge the degree of
cooling because it is the most readily accessible
fruit. A large temperature gradient within the pal-
let ofblueberries could exist when the top fruit of
the first container has reached 7/8 cooling. This
shows that care must be taken when choosing a
fruit to measure the temperature to determine
when cooling is completed.

Condensation in a package of berries prevents
the berries from being easily seen by consumers
and can potentially wet the berries, although
research indicates condensation does not increase
the incidence of decay [13]. Since condensation in
packages is perceived as a problem by marketers
and consumers, the packages should be designed to
prevent condensation. Condensation in a package
is a function of the amount of water vapor inside
the package, the transpiration rate of blueberries,
and the temperature and relative humidity in the
cold room. Warm blueberry packages placed in a
cold room are susceptible to condensation because
the package temperature drops rapidly below the
dew point temperature. Since blueberries are
usually packed warm and then cooled, the package
should remain free of condensation during any
change of temperature. The top of the package
should be designed to reduce water loss from the
berries, at the same time the package should allow
enough ventilation so as to not increase the cooling
time and to prevent condensation inside the pack-
age. Use of a perforated top was found to be the
best solution [6].

Refrigerated storage, and shipping
After precooling, blueberries should be stored
briefly in refrigerated storage prior to shipment.
Figure 8 illustrates that forced-air cooling is 12 to
16 times faster than still-air (room) cooling [2]. The
cooling rate would have been faster if the cooling
room air was at the recommended temperature
(0OC (320F)) rather than 70C (44F). Refrigerated
trucks should be precooled prior to loading the
precooled blue-berries. After precooling, top icing
of blueberries is not desirable during holding or
transport.

Modified atmosphere
Refrigeration is sometimes supplemented with
modified atmosphere during transit or storage.
With solid loads, the modified atmosphere may be


80

75
E.
E 70
C
665


Blueberry Cooling Tests
Comparison of Forced nod Still Air Averages


0 20 40 .60 s0 100 120
Minutes of Cooling
.Forced Air Stil Air
American- Burgaw 65/90
Room Air Temp. 44 F
Figure 8. Comparison of averages of still and forced-air
cooling [2].

established for the entire transport vehicle. Plastic
shrouds can be placed over individual pallets
equipped with a base that can be sealed. Pallet
bags are installed after cooling, usually just before
loading for transport. Carbon dioxide (CO2) is then
injected into the package to establish the desired
atmosphere. Use of plastic films with selected per-
meability to control the carbon dioxide and oxygen
within the individual containers has also shown
promise. Elevated levels of CO2 (10 to 30 percent)
slow the respiration rate of the fruit and reduce the
activity of decay causing organisms, thus extending
storage and market life. Increasing CO2 (10 to 30
percent) reduces the respiration rate and the inci-
dence of decay through direct or indirect effects on
pathogens. Lowering 02 levels can reduce the res-
piration rate of the fruit. Optimal concentrations of
5-10% 02 and 15-20% CO2 are recommended for
blueberries. CO2 atmospheres of 30 percent or
greater can cause off-flavor [7].

Management guidelines
The following management guidelines or recom-
mendations summarize the important postharvest
information discussed above.

Blueberries should be handled gently at all times
to maintaining quality since they are so easily
bruised. Bruised berries are very susceptible to
decay. Anytime a fruit is bruised, the bruised area
will discolor. In addition, bruising increases water
loss and enhances softening. Only sound fruit
should be shipped, because decay fungi can easily
spread throughout each shipping container. Ber-
ries without small dry stem scars are particularly
perishable. Strict grading should eliminate out of







grade berries. It is important to acknowledge that
while proper postharvest cooling and handling
techniques can help maintain product quality, the
quality packed can never be improved.

Cartons should not be overfilled because stack-
ing will cause crushing. After packing, blueberries
should be kept in the shade and transported to the
cooler as soon as possible. The temperature of
harvested blueberries in the field can be as high as
300C (860F), and even higher when exposed to sun;
and when fruits are allowed to remain at this
temperature for 4 hours, marketability drops by at
least 40 percent. Again, very careful handling of
the packed blueberries is essential to maintaining
quality.

A large percent of the rabbiteye blueberry crop
that is destined for the fresh market is machine-
harvested into field lugs. These lugs are hauled
into the packinghouse where they often sit for
several hours until the packingline can handle
them. Some growers pick blueberries mechanically
between 10 PM and 10 AM, if possible, to take
advantage of lower field temperatures. Others try
to lower the temperature of these lugs to 70F or
lower prior to packing. The lugs must not be cooled
below the dew point temperature in the packing-
house or condensation will form on the cold
berries when they are exposed to the warmer
packinghouses air.

A well designed forced-air cooler should be main-
tained at a constant temperature near 0C (320F).
As noted above, the air flow rate has a definite
effect on the cooling rate of blueberries in cartons,
and new container designs can improve cooling effi-
ciency. A cooling schedule should be developed for
the forced-air cooler to maximize efficiency. Use of
a schedule allows cooling times to be adjusted
based on the initial temperature of the berries and
prevents inadequate or excessive precooling
resident time.

Temperatures should be measured with a
reliable electronic thermometer. Fruit pulp tem-
peratures should be taken prior to precooling and
during precooling. Fruit temperatures should be
measured on the warm side of the cooler (inside of
the stack in systems that draw air through the
berries; outside of the stack in systems which blow
air through the berries). Care should be taken in
sampling the blueberry temperatures to determine
when cooling is completed. There is a large differ-
ence in the temperature between the fruit near the


air inlet and the fruit in the last container down-
stream. Precooler personnel should be trained to
use proper blueberry temperature measurement
techniques. Leaving blueberries in the forced-air
cooler longer than necessary can lead to undesir-
able water loss because of rapid air movement. On
the other hand, inadequate cooling can lead to
rapid deterioration due to high temperatures.

Following cooling, blueberries should be stored
in a cold room maintained at -0.5-0,C (31-320F), for
the shortest time possible. The cold room tempera-
ture should be colder than the temperature of the
berries leaving the precooler. In addition to ineffi-
cient use of refrigeration, berries that have been
cooled and then allowed to rewarm (causing
moisture to condense on them) are susceptible to
decay. Humidity as well as temperature must be
controlled in storage facilities. If the air inside the
storage room is too dry, water will evaporate from
the blueberries and they will become soft and shriv-
eled. At a storage room temperature of-0.5 to 0C
(31 to 320F), the relative humidity should be from
90 to 95 percent. Much of the water that evapo-
rates from the fruit is absorbed into or passes
through the packing materials and condenses on
the inside surfaces of the room. Under certain
atmospheric conditions, it may be necessary to add
moisture with a humidification system to maintain
the relative humidity.

Trailers that are to carry blueberries should be
precooled to -0.5 to 0C (31 to 320F) prior to
loading. Also, extreme care must be exercised in
loading palletized units to prevent shifting during
transit by using strapping and corner boards.
Proper bracing is a must for palletized blueberry
shipments. The pallet units should be loaded away
from the walls to prevent outside heat from
transferring directly into the berries.

Summary
This publication presents cooling requirements,
cooling methods, quality parameters, and manage-
ment guidelines for maintaining the quality of
Florida blueberries. Studies conducted to establish
the relationship between condensation and con-
tainer design and the effects of new container de-
signs on cooling rates of blueberries are discussed.
Management guidelines or recommendations to the
packinghouse operators concerning possible system
performance improvements are presented, such as
increasing resident time within the forced-air
precooler to achieve better cooling or lowering the
cold room temperature to prevent warming of







precooled blueberries. To insure delivery of a high-
quality product, growers need to grow and harvest
high-quality blueberries and maintain product
quality after harvest with the right precooling,han-
dling, and storage methods.

References
1. Arifin, B.B. and K.V. Chau. 1988. Cooling of
strawberries in cartons with new vent hole
designs. Trans. ASHRAE. Vol. 94 (1):
1415-1426.

2. Boyette, M.D. 1990. Enhancing quality consis-
tently in packaged blueberries with forced-air
cooling. N.C. State Univ., Dept. of Biological
and Agricultural Engineering Report to the
Southeastern blueberry council.

3. Crocker, T. E. 1990. Survey of southern high-
bush and rabbiteye blueberries in Florida.
Proc. Fla. State Hort. Soc. 102:204-206.

4. Dekazos, E.D. and C.J.B. Smit. 1976. Effect of
variety, packaging and storage conditions on
the shelf life and quality of rabbiteye blue-
berries. Ga. Agr. Res. 18:19-23.

5. Eck, P. 1988. Blueberry Science. Rutgers
University Press. New Brunswick, N.J.

6. Emond, J. -P., K.V. Chau, and J. K. Brecht.
1991. New retail package for blueberries. Ag.
Eng. Res. Report, University of Florida.

7. Hardenburg, R. E., A. E. Watada, and C. Y.
Wang. 1986. The commercial storage of fruits,
vegetables, and florist and nursery stocks.


Agricultural Handbook No. 66. U.S. Depart-
ment of Agriculture. Washington, D.C.

8. Kader, A.A., R.F. Kasmire, F.G. Mitchell, M.S.
Reid, N.F. Sommer, and J.F. Thompson. 1985.
Postharvest technology of horticultural crops.
California Coop. Ext. Serv. Pub. 3311.
9. Lyrene, P.M. and T.E. Crocker. 1990. Com-
mercial blueberry production in Florida. Univ.
FL, IFAS, Fruit Crops Department Special
Series SS-FRC-002.

10. Miller, W.R., R.E. McDonald, E.F. Melvin, and
KA. Monroe. 1984. Effect of package type and
storage time/temperature on weight loss, firm-
ness, and spoilage of rabbiteye blueberries.
HortScience 19:638-640.

11. Miller, W.R., R.E. McDonald, and T.E
Crocker. 1988. Fruit quality of rabbiteye
blueberries as influenced by weekly harvests,
cultivars, and storage duration. HortScience
23:182-184.

12. Mitchell, F.G., R. Guillou, and R.A. Parsons.
1972. Commercial cooling of fruits and veg-
etables. California Agr. Expt. Sta. Man. 43.

13. Moore, J.N. 1987. Post-harvest handling of
fresh market blueberries. Proc. Ark. St. Hort.
Soc. 107:92-95.

14. Sargent, S.A., M.T. Talbot, and J.K. Brecht.
1991. Evaluating precooling methods for veg-
etable packinghouse operations. Univ. FL,
IFAS, Vegetable Crops Department Special
Series SS-VEC-47.















































































COOPERATIVE EXTENSION SERVICE,UNIVERSITY OF FLORIDA, INSTITUTE OF FOODANDAGRICULTURAL SCIENCES, JohnT.Woeste,
Director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and June
30,1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institutions that
function without regard to race, color, sex, age, handicap or national origin. Single copies of extension publications (excluding 4-H and youth
publications) are available free to Florida residents from county extension offices. Information on bulk rates or copies for out-of-state purchasers
is available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Floida, Gainesville, Forida3261 1. Before publicizing
this publication, editors should contact this address to determine availability. Printed 5/92.




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