Title Page
 Front Matter
 Table of Contents
 Citrus pulp and molasses
 Citrus peel oil
 Citrus alcohol
 Citrus feed yeast
 Citrus seed oil
 Citrus bland syrup
 Citrus pectin
 Other potential by-products of...

Group Title: Bulletin / University of Florida. Agricultural Experiment Station ;
Title: Citrus by-products of Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00027148/00001
 Material Information
Title: Citrus by-products of Florida commercial production methods and properties
Series Title: Bulletin / University of Florida. Agricultural Experiment Station ;
Alternate Title: Citrus by products of Florida
Physical Description: 56 p. : ill. ; 23 cm.
Language: English
Creator: Hendrickson, Rudolph
Kesterson, J. W
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville, Fla
Publication Date: 1951
Copyright Date: 1951
Subject: Citrus fruit industry -- By-products -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 54-56).
Statement of Responsibility: R. Hendrickson and J.W. Kesterson.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00027148
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: ltuf - AEN6404
oclc - 18266244
alephbibnum - 000925748

Table of Contents
    Title Page
        Page 1
    Front Matter
        Page 2
        Page 3
    Table of Contents
        Page 4
        Page 5
        Page 6
    Citrus pulp and molasses
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
    Citrus peel oil
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
    Citrus alcohol
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
    Citrus feed yeast
        Page 34
        Page 35
        Page 36
    Citrus seed oil
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
    Citrus bland syrup
        Page 44
        Page 45
        Page 46
        Page 47
    Citrus pectin
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
    Other potential by-products of citrus
        Page 53
        Page 54
        Page 55
        Page 56
Full Text
FEB7 1952

Bulletin 487 December 1951


Citrus By-Products of Florida

Commercial Production Methods and Properties


Single copies free to Florida residents on request to


Frank M. Harris, Chairman, St. Petersburg J. Francis Cooper, M.S.A., Editor
Hollis Rinehart, Miami Clyde Beale, A.B.J., Associate Editor
Eli H. Fink, Jacksonville L. Odell Griffith, B.A.J., Asst. Editor
George J. White, Sr., Mount Dora J. N. Joiner, B.S.A., Assistant Editor s
Mrs. Alfred I. duPont, Jacksonville
George W. English, Jr., Ft. Lauderdale ENTOMOLOGY
W. Glenn Miller, Monticello
W. F. Powers, Secretary, Tallahassee A. N. Tissot, Ph.D., Entomologist
L. C. Kuitert, Ph.D., Associate
EXECUTIVE STAFF H. E. Bratley, M.S.A., Assistant
SF. A. Robinson, M.S., Asst. Apiculturist
J. Hills Mille, Ph.D., Presidentfor Agr. R. E. Waites, Ph.D., Asst. Entomologist
J. Wayne Reitz, Ph.D., Provost for Agr.3
Willard M. Fifield, M.S., Director
J. R. Beckenbach, Ph.D., Asso. Director HOME ECONOMICS
L. 0. Gratz, Ph.D., Asst. Dir., Research
Geo. F. Baughman, M.S., Business Mgr.s Ouida D. Abbott, Ph.D., Home Econ.1
Rogers L. Bartley, B.S., Admin. Mgr.3 R. B. French, Ph.D., Biochemist
Claranelle Alderman, Accountant3
MAIN STATION, GAINESVILLE G. H. Blackmon, M.S.A., Horticulturist'
F. S. Jamison, Ph.D., Horticulturist s
AGRICULTURAL ECONOMICS Albert P. Lorz, Ph.D., Horticulturist
H. G. Hamilton, Ph.D., nA 4Economist's R. K. Showalter, M.S., Asso. Hort.
H. G. Hamilton, Ph.D., Agr. Economist R. A. Dennison, Ph.D., Asso. Hort.
R. E. L. Greene, Ph.D., Agr. Economist 3 R. H. Sharpe, M.S., Asso. Horticulturist
M. A. Brooker, Ph.., Ar. Economist V. F. Nettles, Ph.D., Asso. Horticulturist
Zach Savage. M.S.A., Associate F. S. Lagasse, Ph.D., Asso. Hort.2
A. H. Spurlock, M.S.A., Associate R. D. Dickey, M.S.A., Asso. Hort.
D. E. Alleger, M.S., Associate L. H. Halsey, M.S.A., Asst. Hort.
D L. Brooke, M.S.A., Associate C. D. Hall, Ph.D., Asst. Horticulturist
M. R. Godwin, Ph.D., Associate 3 Austin Griffiths, Jr., B.S., Asst. Hort.
"H. W. Little, MS., Assistant S. E. McFadden, Jr., Ph.D., Asst. Hort.
Tallmadge Bergen, B.S., Assistant C. H. van Middelem, Ph.D., Assistant
D. C. Kimmel, Ph.D., Assistant
W. E. McPherson, M.S., Economist 3
J. F. Lankford, B.S., Agr. Statistician LIBRARY
Orlando, Florida (Cooperative USDA) Ida Keeling Cresap, Librarian
G. Norman Rose, B.S., Asso. Agr. Economist
J. C. Townsend, Jr., B.S.A., Agr. PLANT PATHOLOGY
Statistician 2
J. B. Owens, B.S.A., Agr. Statistician W. B. Tisdale, Ph.D., Plant Pathologist 3
Phares Decker, Ph.D., Plant Pathologist
AGRICULTURAL ENGINEERING Erdman West, M.S., Mycologist and Botanist
Frazier Rogers, M.S.A. Agr. Engineer s Robert W. Earhart, Ph.D., Plant Path.2
J. M. Johnson, B.S.A.E., Agr. Eng.3 Howard N. Miller, Ph.D., Asso. Plant Path.
J. M. Myers, B.S. Asso. Agr. Engineer Lillian E. Arnold, M.S., Asst. Botanist
R. E. Choate, B.S.A.E., Asso. Ar. Eng. C. W. Anderson, Ph.D., Asst. Plant Path.
A. M. Pettis, B.S.A.E., Asst. Agr. Eng.s s
J. S. Norton, M.S., Asst. Agr. Eng. POULTRY HUSBANDRY

AGRONOMY N. R. Mehrhof, M.Agr., Poultry Hush.13
Fred H. Hull, Ph.D., Agronomist' J. C. Driggers, Ph.D., Asso. Poultry Husb.
G. B. Killinger, Ph.D., Agronomists
H. C. Harris, Ph.D., Agronomist SOILS
R. W. Bledsoe, Ph.D., Agronomist
W. A. Carver, Ph.D., Associate F. B. Smith, Ph.D., Microbiologist la
Darrel D. Morey, Ph.D., Associate Gaylord M. Volk, Ph.D., Soils Chemist
Fred A. Clark, B.S., Assistant J. R. Henderson, M.S.A., Soil Technologist 3
Myron C. Grennell, B.S.A.E., Assistant J. R. Neller, Ph.D., Soils Chemist
E. S. Horner, Ph.D., Assistant Nathan Gammon, Jr., Ph.D., Soils Chemist
A. T. Wallace, Ph.D., Assistant Ralph G. Leighty, B.S., Asst. Soil Surveyor 3
D. E. McCloud, Ph.D., Assistant 3 G. D. Thornton, Ph.D., Asso. Microbiologist 3 4
C. F. Eno, Ph.D., Asst. Soils Microbiologist *
ANIMAL HUSBANDRY AND NUTRITION H. W. Winsor, B.S.A., Assistant Chemist
R. E. Caldwell, M.S.A., Asst. Chemist 3
T. J. Cunha, Ph.D., An. Husb.1 V. W. Carlisle, B.S., Asst. Soil Surveyor
G. K. iavis, Ph.D., Animal Nutritionist3 James H. Walker, M.S.A. Asst. Soil
J. E. Pace, M.S., Asst. An. Husb.' Surveyor
S. John Folks, M.S., Asst. An Husb. S. N. Edson, M.S., Asst. Microbiologist
Katherine Boney, B.S., Asst. Chem. lFed E. Koehler, Ph.D., Asst. Soil Micro-
A. M. Pearson, Ph.D., Asso. An. Husb.' biologist
John P. Feaster, Ph.D., Asst. An. Nutri. William K. Robertson, Ph.D., Asst. Chemist
H. D. Wallace, Ph.D., Asst. An. Husb. 0. E. Cruz, B.S.A., Asst. Soil Surveyor
M. Koger, Ph.D., An. Husbandman W. G. Blue, PhD., Asst. Biochemist
DAIRY SCIENCE J. G. A. Fiskel, Ph.D., Asst. Biochemist
E. L. Fouts, Ph.D., Dairy Tech.1 VETERINARY SCIENCE
R. B. Becker, Ph.D., Dairy Husb.3
S. P. Marshall, Ph.D., Asso. Dairy Husb.3 D. A. Sanders, D.V.M., Veterinarian'
W. A. Krienke, M.S., Asso. in Dairy Mfs.3 M. W. Emmel, D.V.M., Veterinarians
P. T. Dix Arnold, M.S.A., Asst. Dairy Husb.' C. F. Simpson, D.V.M., Asso. Veterinarian
Leon Mull, Ph.D., Asso. Dairy Tech. L. E. Swanson, D.V.M., Parasitologist
H. Wilkowske, Ph.D., Asst. Dairy Tech. Glenn Van Ness, D.V.M., Asso. Poultry
James M. Wing, M.S., Asst. Dairy Husb. Pathologist

Geo. D. Ruehle, Ph.D., Vice-Dir. in Charge
NORTH FLORIDA STATION, QUINCY D. 0. Wolfenbarger, Ph.D., Entomologist
Francis B. Lincoln, Ph.D., Horticulturist
Robert A. Conover, Ph.D., Plant Path.
J. D. Warner, M.S., Vice-Director in Charge John L. Malcolm, Ph.D., Asso. Soils Chemist
R. R. Kincaid, Ph.D., Plant Pathologist R. W. Harkness, Ph.D., Asst. Chemist
L. G. Thompson, Ph.D., Soils Chemist R. Bruce Ledin, Ph.D., Asst. Hort.
W. C. Rhoads, M.S., Entomologist J. C. Noonan, M.S., Asst. Horticulturist
W. H. Chapman, M.S., Asso. Agronomist
Frank S. Baker, Jr., B.S., Asst. An. Hush. WEST CENTRAL FLORIDA STATION,
Mobile Unit, Monticello William Jackson, B.S.A., Animal Husband-
R. W. Wallace, B.S., Associate Agronomist man in Charge

Mobile Unit, Marianna
W. G. Kirk, Ph.D., Vice-Director in Charge
R. W. Lipscomb, M.S., Associate Agronomist E.. Hodges Ph.D., Agronomist
D. W. Jones, M.S., Asst. Soil Technologist
Mobile Unit, Pensacola
R. L. Smith, M.S., Associate Agronomist CENTRAL FLORIDA STATION, SANFORD
R. W. Ruprecht, Ph.D., Vice-Dir. in Charge
J. W. Wilson, Sc.D., Entomologist
Mobile Unit, Chipley P. J. Westgate, Ph.D., Asso. Hort.
J. B. White, B.S.A., Associate Agronomist Ben. F. Whitner, Jr., B.S.A., Asst. Hort.
Geo. Swank, Jr., Ph.D., Asst. Plant Path.
A. F. Camp, Ph.D., Vice-Director in Charge WEST FLORIDA STATION, JAY
W. L. Thompson, B.S., Entomologist C. E. Hutton, Ph.D., Vice-Director in Charge
R. F. Suit, Ph.D., Plant Pathologist,
E. P. Ducharme, Ph.D., Asso. Plant Path. H. W. Lundy B.S.A., Associate Agronomist
C. R. Stearns, Jr., B.S.A., Asso. Chemist W. R. Langford, Ph.D., Asst. Agron.
J. W. Sites, Ph.D., Horticulturist
H. O. Sterling, B.S., Asst. Horticulturist SUWANNEE VALLEY STATION,
H. J. Reitz, Ph.D., Horticulturist LIVE OAK
Francine Fisher, M.S., Asst. Plant Path.
I. W. Wander, Ph.D. Soils Chemist G. E. Ritchey, M.S., Agronomist in Charge
J. W. Kesterson, M.S., Asso. Chemist
R. Hendrickson, B.S., Asst. Chemist GULF COAST STATION, BRADENTON
Ivan Stewart, Ph.D., Asst. Biochemist E L. Spencer, Ph.D., Soils Chemist in Charge
D. S. Prosser, Jr.. B.S., Asst. Horticulturist E. G. Kelsheimer, Ph.D., Entomologist
R. W. Olsen, B.S., Biochemist
. W. enel, Jr., Ph.D., Chemist David G. Kelbert, Asso. Horticulturist
Alvin H. Rouse, M.S., Asso. Chemist Robert O. Magie, Ph.D., Plant Pathologist
H. W. Ford, Ph.D., Asst. Horticulturist J. M. Walter, Ph.D., Plant Pathologist
L. C. Knorr, Ph.D., Asso. Histologist Donald S. Burgis, M.S.A., Asst. Hort.
R. M. Pratt, Ph.D., Asso. Ent.-Pathologist C. M. Geraldson, Ph.D., Asst. Hort.
J. W. Davis, B.S.A., Asst. Ent.-Path. W. G. Cowperthwaite, Ph.D., Asst. Hort.
W. A. Simanton, Ph.D., Entomologist
E. J. Deszyck, Ph.D., Asso. Horticulturist
C. D. Leonard, Ph.D., Asso. HorticulturistATOR
I. Stewart, M.S., Asst. Biochemist FIELD LABORATORIES
W. T. Long, M.S., Asst. Horticulturist Watermelon, Grape, Pasture-Leesburg
M. H. Muma, Ph.D., Asst. Entomologist
F. J. Reynolds, Ph.D., Asso. Hort. C. C. Helms, Jr., B.S., Asst. Agronomist 4

R. V. Allison, Ph.D., Vice-Director in Charge A. N. Brooks, Ph.D., Plant Pathologist
Thomas Bregger, Ph.D., Sugar Physiologist
J. W. Randolph, M.S., Agricultural Engr. Vegetables-Hastings
W. T. Forsee, Jr., Ph.D., Chemist A. H. Eddins, Ph.D., Plant Path. in Charge
R. W. Kidder, M.S., Asso. Animal Husb. E. N. McCubbin, Ph.D., Horticulturist
C. C. Seale, Asso. Agronomist
N. C. Hayslip, B.S.A., Asso. Entomologist
E. A. Wolf, M.S., Asst. Horticulturist Pecans-Monticello
W. H. Thames, M.S., Asst. Entomologist A. M. Phillips, B.S., Asso. Entomologist 2
W. N. Stoner, Ph.D., Asst. Plant Path. John R. Large, M.S., Asso. Plant Path.
W. A. Hills, M.S., Asso. Horticulturist
W. G. Genung, B.S.A., Asst. Entomologist
Frank V. Stevenson, M.S., Asso. Plant Path. Frost Forecasting-Lakeland
R. H. Webster, Ph.D., Asst. Agronomist Warren O. Johnson, B.S., Meteorologist
Robert J. Allen, Ph.D., Asst. Agronomist
V. E. Green, Ph.D., Asst. Agronomist Head of Department
J. F. Darby, Ph.D., Asst. Plant Path. 2 In cooperation with U. S.
H. L. Chapman, M.S.A., Asst. An. Hush. a Cooperative, other divisions, U. of F.
Those. G. Bowery, Ph.D., Asst. Entomologist On leave.


INTRODUCTION -...... ... ............................. 5

CITRUS PULP AND MOLASSES ...........--- ........... ................... 7
General Processing Procedure ............... --... ---...- ..--- .......... 9
Citrus Pulp ......----.......--------............... ................... ......... 10
Citrus Mclasses ..- ---..--- ..----- ............... ....... ................. 13
Citrus Stripper Oil ......... ...... ---..... .............. ..... ... ....... .......... 14
Processing Equipment ............------..-- --------.......-....-.......... 15

CITRUS PEEL OIL ... ...............------------------------..... .... ........... ..... 22
Coldpressed Oils ......... ............------- ...--..-- .....-- ...-- ....... 22
Distilled Oils -......--..--.....-..- -....... --.... ........... ................. 27
Typical Analyses for Coldpressed and Distilled Oils .............................. 27
Utilization of Citrus Peel Oil -............-...... ... ...-- -..................... 28

CITRUS A LCOHOL ................................................... ........ .....- -...... 28
General Processing Procedure --..........--....--- -......--...-- ........... 28
Utilization of Citrus Alcohol .............. ........ .... ......... .....-............ 34

CITRUS FEED YEAST ..------.................------....- ......................... 34
General Processing Procedure ................... -.... .. .............----- --.. .... 35
Utilization and Composition ..-------............. .--. ......................... 36

CITRUS SEED OIL ................... .... --------------------- -- .... .......... 37
General Processing Procedure ....................................................... 37
Typical Analyses for Citrus Seed Oils, Meal and Hulls ........................ 41
Utilization of Citrus Seed Oils, Meal and Hulls .----............--............... 44

CITRUS BLAND SYRUP .....................................-................ ........ 44
General Processing Procedure .................. ...---- .............. ..... 45

CITRUS PECTIN ........-.. .....---------..........-................... 48
General Processing Procedure ...--.. -- ------........ ...............-- ......... 48
Utilization of Citrus Pectin ........... ...... .............. ................... 51

OTHER POTENTIAL BY-PRODUCTS OF CITRUS .........--....-- ...- -................... 53

ACKNOWLEDGMENTS ................. -- -..-.......-....- ....... ................ ..... 53

LITERATURE CITED ..... .....................---------- -- ........ ........-. ....... ....... 54

Citrus By-Products of Florida

Commercial Production Methods and Properties



Since the 1920-30 decade the processing of citrus fruits has
grown rapidly to be a vast and important part of the Florida
citrus economy. The industry has grown to such proportions
in recent years, particularly since the development of frozen
citrus juice concentrate in 1945, that more than half the Florida
orange and grapefruit crop is now processed, as seen in Table 1.

Season Oranges Processed Grapefruit Processed
1,000 Boxes Percent 1,000 Boxes I Percent
1941-42 ........ 4,271 16 10,143 53
1943-44 ........ 11,011 24 20,446 66
1945-46 ........ 19,220 39 22,136 69
1947-48 ........ 30,421 52 19,451 59
1949-50 ... 34,707 59 13,489 55

ORANGES (37, 39, 42, 51).

Physical Chemical

Component | Percent I1 Component Percent

Juice .................. 40-45 Water ......................... .... ......... 86-92
Sugars ........................................ 5-8
Flavedo Pectin ............... ..... ................. 1-2
(outer peel) 25-35 Glucoside ..................................... 0.1-1.5
Pentosans .................................... 0.8-1.2
Albedo Acids (citric mostly) ...-............ 0.7-1.5
(inner peel) .. 10-18 Fiber ..................................... ...... 0.6-0.9
Protein ........................... .............. 0.6-0.8
Rag and pulp .... 10-12 Fat .......................... .......... ... 0.2-0.5
Essential oil .......... ...... ............. 0.2-0.5
Seeds .............. 0-4 Minerals (K, Mg, Ca, P, etc.) ... 0.5-0.9

Since over half the fruit is peel, pulp and seed (Table 2), a
whole new industry was born out of necessity to solve a most

1Assistant Chemist, Citrus Experiment Station, Lake Alfred, Florida.
2Associate Chemist, Citrus Experiment Station, Lake Alfred, Florida.
3 Figures in parentheses (italic) refer to Literature Cited.

Rot ___y _Bsket__Shaker Sh k O

S. s ....

sIce yr Hyd ic Sood rgeg

1AS 1 dF n.d,

Tonk ^e, ^^''e"J ^ Jhon* ^ __| ra an toP-Sfo"t".o C cOlln c.1oI""ls k
"- c b v |res M ola s' s
Supi eol n

I, t Und. ,1 2 en r

SWe Ps--at.d

Fig. .A schematic diagram showing the overall manufacture of citrus by-products.

Fig. 1.-A schematic diagram showing the overall manufacture of citrus by-products.

Citrus By-Products of Florida, 7

difficult waste disposal problem. In the 1949-50 season, when
a total of 48 million boxes of oranges and grapefruit were
processed, two million tons of refuse remained to be disposed
of by the citrus by-product industry. Today processing by-
products is an essential part of the citrus industry and is also
important to other industries. The rapidly-growing Florida cattle
industry utilizes large tonnages of two primary by-products,
dried citrus pulp and citrus molasses, as stock feeds.
The manufacture of the various by-products is best visualized
by consulting Fig. 1, wherein the handling of citrus fruits from
the time they are picked is shown schematically. The canning
plant receives oranges, grapefruit and tangerines, both from
the field and from the packinghouse. Packinghouse fruit usually
includes the larger and smaller sizes not generally shipped, as
well as other sizes having surface blemishes. All fruit is made
to pass over grading belts where split and bruised fruits are
rejected. The peel, rag and seeds from the juice extractors
and finisher are combined with these rejected fruits and become
the source of the by-products of citrus. Dried citrus pulp,
molasses and citrus peel oil are the three primary by-products.
However, citrus seed oil, alcohol, pectin, bland syrup and feed
yeast have been produced to a lesser extent.
The production of citrus by-products is now firmly established
as an integral part of almost every citrus canning plant, and
in some years the proceeds from by-products could spell the
difference between profit and loss to the processors.

Dried citrus pulp and citrus molasses are discussed together
at this point because the processing procedure in the early
stages is identical and manufacture of both products can be
accomplished in a balanced operation.
The profitable utilization of the residue of citrus fruit for the
past 25 years has resulted mainly from the production of dried
citrus pulp. Approximately one million tons of this pulp have
been produced in Florida alone since its value as a feed was first
shown. Many investigators (4, 5, 9, 10, 26, 29, 35, 41) have
shown it to be an excellent bulky carbohydrate feed for both
beef and dairy cattle, with dried grapefruit peel having the
further advantage of containing factors which stimulate milk
production in dairy cows (3, 11).
Since the 1941-42 canning season, when citrus molasses was




rJx \.^


Citrus By-Products of Florida 9

first produced, there has been an expansive growth in the pro-
duction of this product. It has proved to be an excellent carbo-
hydrate concentrate, which not only is a feed in itself but also
is used successfully to ensile non-saccharin grasses, to pelletize
dried citrus pulp and to increase the carbohydrate content of
dried citrus pulp and mixed feeds (5). Recently a citrus mo-
lasses fortified with urea and containing an equivalent of 10 to
15 percent crude protein has been made available for stock
General Processing Procedure
The production of dried citrus pulp and molasses commences
with the accumulated citrus cannery residue consisting of peel,
rag and seeds which represent approximately 50 to 60 percent
of the whole fruit. Large tonnages of these residues, accumu-
lated and held in unprotected open bins, are passed continually
to hammer mills or shredders (Fig. 2), where the peel is cut
by rotating hammers or knives into pieces approximately 1/4 by
34 inch. About 0.3 to 0.6 percent lime is added as a powder
or slurry immediately before, during or after comminution of
the peel. A rotating screw conveyor both mixes and conveys
the limed pulp to a pug mill or curing bin. Local alkalinity
changes the color of the chopped peel to a rather bright yellow,
then slowly to a greyish straw color as the lime reacts with the
acidic components. Although experienced operators are able to
judge the proper quantity of lime to add by feel and consistency
of the peel, automatic control instruments are becoming preva-
lent in the industry. The high local alkalinity resulting from the
slow diffusion of lime is indirectly responsible for a rapid de-
grading and demethylating of pectins present. Preciptation
and coagulation of the pectin with lime causes the cells to break
down and the lime to permeate the peel thoroughly. The pH
of the unbound liquor is then lowered and at the same time
syneresis sets in, facilitating removal of the press liquor.
Processes using a pug mill, which might be described as a huge
modified screw conveyor, allow approximately 15 to 25 minutes
curing time prior to pressing. Those using large holding bins
generally allow about half an hour for the lime to react. In
the laboratory where the peel was chopped into smaller pieces,
five minutes reaction time appeared sufficient, although longer

4 Fig. 2.-Hammer mill. (Photograph courtesy Kuder Citrus Pulp Co.,
Lake Alfred.)

10 Florida Agricultural Experiment Stations

time aided the expulsion of press liquor. After curing, the peel
is carried by conveyor to continuous mechanical presses, such
as the Davenport, Louisville or Zenith described later. All
three types are used in Florida. These continuous mechanical
presses squeeze the limed peel, reducing its moisture content
from approximately 82 to 72 percent or lower, and in so doing
obtain about 60 percent of the weight of the original residue as

1000 Boxes of Fruit
88,000 Lbs.


40,480 Lbs. of Juice
(Approx. 1382 Cases No.2 Cons)

47,520 Lbs. of Peel, Pulp 8 Seeds
82.0 % Moisture
8544 Lbs. of Dry Matter

Shred, Lime (0.3-0.6%)
Cure & Press

19,008 Lbs. of Press Coke 28,512 Lbs. of Press Juice
S72.0 % Moisture 88.7 % Moisture
5322 Lbs. of Dry Matter 3222 Lbs. of Dry Matter

50 Lbs. of Evaporate 855 Lbs. of
Evaporate 13,223 Lbs. Steam Distilled Water in Flash Chamber
of Water in Dryer Oil
from Evaporate 23,182 Lbs. of Water
Condensate in Multiple Effect Evaporator
5785 Lbs. of Dried Citrus Ms
Pulp 4475 Lbs. of Citrus Molasses
8.0 % Moisture 395 Gallons
5322 Lbs. of Dry Matter 28.0 % Moisture
3222 Lbs. of Dry Matter
Approx. I Ton of Sugar

Fig. 3.-Flow and material balance sheet for the processing of citrus
residues into dried pulp and molasses.

Citrus By-Products of Florida 11

press liquor. The flow diagram for this commercial process is
shown in Fig. 3.
In Texas a somewhat different arrangement is employed (44).
Large curing bins of 10-ton capacity are filled with limed, chopped
peel. As the bound water is released by the lime it drains and
is collected, reducing the moisture content of the peel from 83.0
to 81.8 percent. This process yields 20 percent press liquor on
the weight of original residue without the aid of mechanical
presses. The apparent high yields of press liquor obtained in this
and the above example are mathematically explained by Pearson's
rule (38), which properly takes into account the numerically
close dry solids content of the press liquor versus the unpressed
peel. At present two processors in Florida are using a procedure
that avoids pressing.

Citrus Pulp
The pressed residue, usually containing 65 to 75 percent mois-
ture, is conveyed to rotating driers where it is dried to 6 or 8
percent moisture. The driers commonly used are the long cylin-
drical rotary drier and the triple pass rotary direct-fired drier
which will be described more completely later. The drier pulp
empties directly from the driers into separators of the cyclone
type, in which the hot gases from the drier are made to whirl
around the inside of a cone. The dried solids fall onto the wall
of the cone while hot gases exhaust to the atmosphere. From
the cone the dried pulp is conveyed to a cooler that usually con-
sists of a rotating drum through which air is passed counter-
current, although open screw conveyors have been used for
cooling. The dried pulp at this point is divided into three
products: the counter-current cooling air carries off the fines
or dust; a rotary screen on the lower end of the cooling drum
separates the portion called citrus meal; and the material carried
through is the dried citrus pulp. The citrus meal is considered
to be of lower quality and is generally sold at a reduced price,
while the fines or dust are even less valuable and are sold usually
as a fertilizer conditioner. For this reason processors have
taken considerable care to operate their plants in such fashion
as to avoid fines and meal. A few processors consider it more
advantageous to burn fines as heating fuel than to bag and
sell them. A typical plant will produce approximately 91 per-
cent dried citrus pulp, 8 percent citrus meal and 1 percent fines.
According to Heid (19), many of the disadvantages attributed

12 Florida Agricultural Experiment Stations

to oil-fired rotary driers, such as excessive kiln temperatures,
burning of fines, lower yield and the fire hazard from bagging
due to sparks, can be eliminated by multiple stage drying. In
the latter operation three kilns maintained at 230 F. can be
used to dry the pulp to 32 percent moisture, and drying is com-
pleted in a fourth kiln at a gas discharge temperature of 1800F.
A steam-tube rotary drier is used advantageously as the fourth
drier, since it allows closer temperature control, but it is gen-
erally more expensive because of the need for a boiler. Exhaust
steam from a cannery, if available, may be used economically
at this stage. Two-stage drying is also done in Texas (44),
using three identical parallel-flow rotary kilns held at 2550F.
in the first stage. Final drying, completed at 200F., reduces
the moisture content from 40 to less than 10 percent. When
pressing is not practiced, as in Texas, sticking sometimes occurs
in the drier because the feed is too wet, but if the feed is too
dry it may be scorched. There is at present considerable debate
as to the most economical drying procedure for producing a
quality product that is bulky and results in a minimum of fines.
Many processors make a sugar-sweet pulp, adding 20 to 30
percent citrus molasses back to this pulp before, during or
after the drying operation. Sometimes more molasses is added,
depending on the marketing area to which the pulp is to be
shipped. Dried citrus pulp is slightly hygroscopic and if proper
care is not taken the product will increase in moisture content
to the point where it will mold and heat while in storage, thereby
lowering the quality of the feed. If the feed is permitted to
heat excessively it can become a definite fire hazard due to
spontaneous combustion.

Component Percent

Crude protein ........................................................... 6.2
Fat ....................................-----.... ...-..----.... 3.5
Crude fiber ....-...--................. .----... ...------.. -----. 13.0
Nitrogen- free extract ............-........-...... ...----. 63.0
A sh .......... ................ ... ..... ...----. 4.3
Dry m matter ...................................... ....................... .. 92.0

Table 3 presents the average feed analysis of dried citrus
pulp calculated from numerous published (3, 9, 25, 30, 35, 40)
and unpublished analyses. Since the product is made by a num-

Citrus By-Products of Florida 13

ber of methods and from a mixture of orange and grapefruit,
there is some variation from sample to sample. The addition of
citrus molasses increases the carbohydrate content and decreases
the fiber content.
Citrus Molasses
Limed peel when pressed yields a press liquor, peel juice or
press juice, however it might be called, that contains 8 to 15
percent total dissolved solids, of which more than half are
sugars. It has a pH ranging from 5.5 to 7.0. After being
released from the peel the press liquor is passed through a
stainless steel shaker screen to eliminate grosser particles and
then is sent to a large holding tank. It is processed quickly
through heat exchangers that raise the temperature to approxi-
mately 2400F., then flashed to atmospheric conditions. This
operation serves four purposes: (1) peel oil is distilled off and
recovered as an additional by-product; (2) the high tempera-
ture kills all spoilage organisms; (3) calcium citrate and other
calcium organic salts with inverted solubilities are precipitated;
and (4) the flocculation of other suspended matter is aided.
Considerable scale is deposited in the high temperature ex-
changer, but this is considered advantageous, since it sub-


Figt 4.-Fow
.............. ... ..^ -T---r

-26099A F __

0 I 0 0

wq.er--- F eo
Vopor -------
Citrus liquor s IS

Fig. 4.-Flow and material balance for a four-body triple-effect evaporator.

14 Florida Agricultural Experiment Stations

stantially decreases scale deposit later in the multiple-effect
evaporator and permits longer periods of operation between
shut-downs. Some processors partially clarify the liquor prior
to its entering the evaporator by settling out suspended matter
in the hot press liquor storage tank. The hot press liquor is
concentrated to 50' Brix in a multiple-effect evaporator and
usually is screened to eliminate the larger scale particles that
may have loosened in the evaporator. A forced circulation
finishing pan completes concentration to 72 to 75' Brix. A
schematic flow diagram for a four-body triple-effect evaporator
is shown in Fig. 4.
In Texas (44) the abundance of natural gas allows the use
of an Ozark submerged burner. The unit is fed a balanced mix-
ture of air and gas to effect initial concentration of the press
liquor by submerged combustion. The press liquor then is
allowed to settle and is concentrated further by the same type
burner prior to going to the multiple-effect evaporators. These
burners bring about a natural carbonation that lowers the pH
to 6.0.
Citrus molasses, as now manufactured in Florida, is required
to meet minimum state standards. It must contain 45 percent
total sugars, expressed as invert sugar, and test not less than
35.50 Brix by double dilution. A typical analysis compiled from
published (20, 21, 30) and unpublished data is shown in Table 4.

Brix ................................ 72.0 Potassium (K) % -........-.... 1.1
Nitrogen-free extract. 62.0 Calcium (Ca) % .------------.. ---.......... 0.8
Total sugars % -............. 45.0 Sodium (Na) % ..-.--.--.. --.... 0.3
Moisture c% .--...----..... 29.0 Magnesium (Mg) % ...-........ 0.1
Reducing sugars % ...... 23.5 Iron (Fe) % .. -................. 0.08
Sucrose % ...............--- ... 20.5 Chlorine (Cl) % ............-......... 0.07
pH .-..................-... 5.0 Phosphorus (P) % ............ 0.07
Carbonate ash % .......... 4.7 Silica (SiO2) % -.........--.---. 0.01
Acid, as anhyd. citric % 4.5 Manganese (Mn) % ......--.... 0.008
Nitrogen % x 6.25 ........ 4.1 Copper (Cu) % ....................... 0.003
Glucoside % .....-......-.... 3.0 Niacin (ppm) ---.---. --.------ 35
Pentosans % .................. 1.6 Riboflavin (ppm) --..---......... 11
Pectin .----..----------.................... 1.0 I Panthothenic acid (ppm) ..... 10
Fat % ..................-.......--.. 0.2 Inositol .-. ----. ---...- ----
Volatile acids c ...---..... 0.04
Fiber .--..--.. ---..-------- 0.00 Viscosity 25C. centipoises... 2000

Citrus Stripper Oil
Stripper oil is obtained as a by-product from the manufacture
of citrus molasses. Citrus press liquor contains 0.20 to 0.50
percent peel oil and, since this oil steam distills readily, 60 to

Citrus By-Products of Florida 15

80 percent of the oil present in the liquor can be recovered by
flashing from 2400F. to atmospheric conditions. Florida has
a potential production of over one million pounds per year, based
on the quantity of citrus molasses made in previous years. Not
all processors are equipped to recover this oil, so yearly pro-
duction is somewhat less. Stripper oil is usually a mixture of
citrus oils, since the press liquor is obtained most often from
"a mixture of orange and grapefruit peel. It frequently possesses
"a fine citrus oil character, marred only by a slight distilled
character, and contains very little of the waxy material ordi-
narily present in expressed citrus oils. Table 5 presents the
physical and chemical properties of this oil.

Stripper Oil Maximum Minimum

Specific gravity 25'C./25'C. .................... 0.8433 0.8398
Refractive index N D ............ ......... 1.4721 1.4713
Optical Rotation c- 25 ..... .. ..... +98.90 95.55
Aldehyde content %- ...........--- ....---- .......- .-.... 1.50 0.47
Ester content % ..............--......- ..--..... -...... 2.46 0.07
Evaporation residue % .-...-........... ....-..-- ..... 0.79 0.03

Since stripper oil contains over 95 percent of d-limonene, it
is considered one of the purest sources for this mono-cyclic
terpene. Bell (6) recognized this oil as an excellent high purity,
low cost source material for making fine organic chemicals. A
synthetic spearmint oil flavor, 1-carvone, already has been
manufactured from this oil. Considerable quantities of citrus
stripper oil are bought yearly by the paint and varnish industry,
where it is recognized as an excellent antiskinning agent. Other
uses for this oil are as an ingredient of clear plastics, as a base
for soap perfumes and as a penetrating oil.

Processing Equipment
Driers.-Driers, or kilns as they are sometimes called, can
be divided into three types. The direct-fired and steam-tube
rotaries are both composed of a long cylindrical shell, usually
8 feet in diameter and 60 feet long. The first type is fired by
oil and hot combustion gases pass directly over the wet pulp.

16 Florida Agricultural Experiment Stations

In the second type the wet pulp and air both are heated by
steam tubes within the shell of the drier. The pressed citrus
pulp moves gradually but continuously through the driers by
virtue of baffles that keep the product moving toward the outlet.
In the direct-fired rotary the heat flow is in the same direction
as the pulp, while in the steam-tube drier the hot air flows
counter-current to the pulp. As previously mentioned, these
driers are sometimes adapted to multiple-stage drying.

Flow of Hot Gases

\ Feed


in | [ Feed

S Header


Sa 0 ^ Hot I Feed
{ Q f QGses -1 out


Fig. 5.-A schematic diagram of three types of driers for citrus pulp.

Citrus By-Products of Florida 17

A third type drier in use is a triple pass parallel heat flow
rotary drier using hot combustion gases from a direct-fired
furnace. Like all rotary driers, it has internal baffles that keep
the pulp turning over and moving slowly through the drier.
The hot gases are carried through with the feed into the cyclone
separator where they are separated. Fig. 5 shows these three
basic types of driers in schematic outline.
Davenport Continuous Press.-A Davenport continuous press
is shown in Fig. 6. The limed, chopped peel is conveyed into

Fig. 6.-Davenport continuous press. (Photograph courtesy Davenport
Machine & Foundry Co., Davenport, Iowa.)


18 Florida Agricultural Experiment Stations

the top opening of an intake hopper and drops between two
large revolving perforated disks, the faces of which come pro-
gressively closer as they approach the discharge port. The in-
creasing pressure expels the press liquor through the minute
opening of the perforated disks. The press liquor drains clear
of the press at the bottom. The fibrous character of the peel
acts as a filtering medium, aiding the screen plates in prevent-
ing the fine solids from passing off with the liquid. The com-
pressed peel is continuously removed by a discharge bar that
forces it out the exit after a three-quarter revolution. The
press, which is completely enclosed, is manufactured in a num-
ber of sizes.
Fig. 7.-Louisville continuous press. (Photograph courtesy General
American Transportation Corp., Louisville, Ky.)

~' -ct

Citrus By-Products of Florida 19

Louisville Continuous Press.-The Louisville continuous roller
type press, shown in Fig. 7, is composed of a sectional, endless
belt of perforated hinged plates which pass continuously over a
series of supporting rolls. Each perforated metal section offers
a pressing surface that passes between a series of paired rolls,
one a supporting roll, the other a pressure roll. As the limed
pulp is fed to the press it forms a fibrous mat that acts as a
filter bed to retain the fine solids. The series of paired rollers
provide an almost continuous wringing action, forcing the press
liquor through the perforated filtering plates and discharging
the compressed pulp at the far end, where the plates pivot about
a hexagonal supporting drum to return underneath.
Zenith Pulp Press.-The Zenith continuous pulp press (Fig. 8)
is essentially a vertical screw press that consists of a heavy,
tapered, screw-type spindle surrounded by a series of downward
deflectors. This spindle is perforated on the lower half and re-
volves at a relatively low speed inside a reinforced cylindrical
screen of stainless steel. The chopped, limed peel enters the
press at the top and during its downward movement is con-
stantly rolled over and continuously forced by screw deflectors
through a restricted, tapered opening, thus being subjected to
increased pressure. Vanes projecting through the outer screen
act to retard and turn over the pulp while it is compressed.
Press liquor is forced through the small perforations of the
outer cylindrical screen, as well as through those of the tapered
spindle. At the bottom the pulp is still under pressure and is
forced through a second restricted tapered opening with further
draining screen to remove more press liquor.
Multiple-Effect Evaporator.-The multiple-effect evaporator
(Fig. 4) is made up of three, four or five evaporators connected
in series, each evaporator being called an effect or body. In
the types used generally in the citrus molasses industry, press
liquor enters the first effect, a vertical cylindrical vessel, passing
through vertical tubes heated externally by steam. At the top
of the tubes the liquor passes into a chamber where water
vapor flashes from the liquid. By lowering the pressure and
thus the temperature at which water boils off in successive
effects, vapors leaving the first effect become steam for the
second, vapors from the second become steam for the third,
until vapors from the last effect go into the barometric con-
denser. With press liquor and other liquids that increase in
viscosity with concentration, a forced feed or single-effect finish-

20 Florida Agricultural Experiment Stations

ing evaporator is used to complete concentration, allowing better
heat transfer and less charring of the final product.

Fig. 8.-Zenith pulp press. (Photograph courtesy Jackson & Church Co.,
Saginaw, Michigan.)

Citrus By-Products of Florida 21

Spray Evaporator.-In this system hot gas from an oil burner
is used to evaporate water from press liquor. A spray of press
liquor is introduced into a steam of very hot gas from an oil

Fig. 9.-Spray evaporator. (Photograph courtesy Dan B. Vincent, Inc.,

i -

i i
I -

_I_ .

22 Florida Agricultural Experiment Stations

burner. The temperature of the two come to equilibrium in a
stainless steel evaporation chamber, and the hot water-laden
gas is separated from the concentrated press liquor in a cyclone
separator. Recirculation or a second effect can be used to ob-
tain further concentration. General practice has been to use
the latent heat of the hot, moist gas in a second effect and to
complete evaporation in a forced feed finishing pan. Several
plants in Florida are using equipment of this type (Fig. 9).
The essential oil is the first product recovered from cannery
refuse. Orange oil, the most useful citrus oil produced in Flor-
ida, commands a price which justifies the operation of a plant
for its recovery.
Citrus oils are contained in oval, balloon-shaped oil sacs or
vesicles located in the outer rind or flavedo of the fruit adjacent
to the chromoplasts. Numerous oil sacs or glands are located
irregularly at different depths in the flavedo of all citrus fruits.
These glands or sac-like intercellular receptacles have no walls
of the usual type, but are bounded by the debris of degraded
tissues. The cells surrounding the oil glands contain an aqueous
solution of sugars, salts, and colloids and exert some pressure
on the glands. Winton and Winton (51) and Braverman (7) de-
scribe the exact location of these oil sacs in their discussion of
the structure of the flavedo of the orange.
To secure the oil from the peel of citrus fruits, oil sacs must
be punctured by either pressure or rasping. Methods of oil
extraction used in Florida were investigated by Kesterson and
McDuff (24) and studies relative to the physical and chemical
properties of Florida citrus oils are discussed in detail.
Coldpressed Oils
General Processing Procedure.-Citrus peel oils are expressed
in Florida by four different types of equipment: (1) Pipkin roll,
(2) screw press, (3) Pipkin juice extractor, and (4) Fraser-
Brace extractor. All of the above methods of extraction give
an emulsion of oil and water. The oil is separated centrifugally
from the aqueous phase by passing the emulsion through a
sludger and then through a polisher. Following separation, the
oil is stored for approximately one week at 320 to 40F. and
during this winterizing treatment undesirable waxy materials
separate from the oil and are allowed to settle. The clear oil
is decanted into stainless steel storage tanks or tin-dipped con-

Citrus By-Products of Florida 23
Fig. 10.-Pipkin roll. (Photograph courtesy Essential Oil Producers, Inc.,


V8" --" I 1.f

A H jl^-^


24 Florida Agricultural Experiment Stations

trainers, which are then maintained at a storage temperature

of about 400F. Air usually is excluded from the container to

prevent deterioration. This is accomplished either by filling

the container full of oil or by displacing the air with carbon




1250 GAL /HR 1 50 GAL /HR.


6000 RPM 43 GAL /HR 175 GAL/HR.
2500 GAL /HR

2457 GAL /HR

2661 GAL./HR. ---- CENTRFUE
S204 GAL/HR 6500 RPM

18000 R PM.
14 GAL /HR.

14 GAL./HR.



F Aig IB. lo a JAlaeST sh*Eitertoi

Fig. 11.-Flow and balance sheet for peel oil recovery using screw press.

Citrus By-Products of Florida 25

Pipkin Roll Method.-A Pipkin roll is shown in Fig. 10. In
this method the oil is expressed by passing peel of the fruit be-
tween two striated rollers of stainless steel that turn in opposite
directions. The distance between the two rollers is adjusted so
that the pressure against the peel is just sufficient to puncture the
oil cells without breaking or rasping the peel. Small striations
or grooves are distributed over the entire surface of the rolls at
a depth sufficient to receive the oil from the oil cells, thereby
keeping it out of contact with the peel and decreasing its ab-
sorption by the albedo of the fruit.
Screw Press Method.-In this method tapered screws press
the crushed peel against a perforated screen, squeezing out the
oil. This operation can be carried out with the screws in either

Fig. 12.-Pipkin juice extractor. (Photograph courtesy Food Machinery
Corp., Lakeland.)


S _. .

26 Florida Agricultural Experiment Stations

a vertical or a horizontal position. Water may or may not be
used in the pressing operation. A typical flow and material
balance sheet for the manufacture of coldpressed citrus peel oil
by the use of screw presses is shown in Fig. 11.
Pipkin Juice Extractor.-The Pipkin juice extractor (Fig. 12)
provides a method whereby both the juice and the peel oil from
whole fruit are secured simultaneously, but in such manner that
they do not come in contact with each other to any great extent.
The machine is of the rotary type and has 24 squeezing heads,
all actuated by a common cam. The extractor is furnished
complete with a feeder mechanism and a built-in electric power
unit. The whole fruit is fed into a squeezing cup where just
enough pressure is applied to remove all of the juice from the
fruit and at the same time rupture the oil cells. The juice and
oil emulsion are collected in separate trough assemblies.


@ @ @ @ @ @

0oQ 000 0 00



Fig. 13.-Cross-section diagram of Fraser-Brace extractor. (Photograph
courtesy Fraser-Brace Engineering Co., New York.)

Citrus By-Products of Florida 27

Fraser-Brace Extractor.-Whole fruit is passed through a
corridor of carborundum rolls in this process, as shown in Fig. 13.
As the fruit passes through the oil extractor it is turned over
and over and abrasive rolls rasp the flavedo from the fruit.
Water sprays are directed onto the fruit and rolls to wash away
the oil and grated peel. The oil and water emulsion is passed
over a screen to remove the suspended solid particles and then
transferred to settling tanks in which it is held from 3 to 12
hours to effect complete settling and allow the emulsion to
break. The machine is completely enclosed and allows very
little loss of oil.
Distilled Oils
Distilled oil of orange, grapefruit or tangerine is secured by
some processors as a by-product in the canning of citrus fruit
juices. Some of the citrus peel oil becomes mixed with the
juice as it is extracted by the various types of juice extractors
used in the canneries. Excessive amounts of peel oil in the
juice are harmful to the quality of canned juice; therefore, in
most canning plants the oil content of the juice is reduced to
a desirable level by passing the juice through a de-oiler. The
juice is usually flashed in the de-oiler, which is operated under
a vacuum of 11 inches (1900F.) to 25.5 inches (1300F.), and
a vapor mixture of oil and water is removed. Then the mixture
of oil and water vapors is condensed and the oil is separated
from the condensate by decanting or centrifuging. Vacuum
steam distilled oils manufactured in this manner will have
properties slightly different from oils obtained by steam dis-
tillation at atmospheric pressure.

Typical Analyses for Coldpressed and Distilled Oils
Table 6 includes typical values for the physical and chemical
characteristics of coldpressed and distilled orange oils produced
in Florida. Similar data for expressed and distilled grapefruit
and tangerine oils are given in Table 7.
The maximum and minimum values for the properties of ex-
pressed and steam distilled Persian lime oil are listed in Table 8.
Also included in this table are results from the analysis of one
sample of steam distilled oil from Meyer lemon. Properties of
Meyer lemon oil indicate that it is predominantly lemon in char-
acter, although the Meyer lemon is commonly believed to be a
natural hybrid.

28 Florida Agricultural Experiment Stations

Utilization of Citrus Peel Oil
During recent years the manufacture of orange oil, as well as
of grapefruit and tangerine oil, has increased to a considerable
extent in Florida. Essential oils, as they are called, find many
and varied uses for the flavoring and scenting of various prod-
uts. These oils are composed of mixtures of hydrocarbons,
oxygenated compounds and non-volatile residue. The hydro-
carbons are primarily terpenes, while the oxygenated compounds
are made up of a variety of compounds-aldehydes, esters, acids,
alcohols, ketones, ethers and phenols. Non-volatile residues con-
sist of resins and waxes. The oxygenated compounds, the prin-
cipal flavoring agents of citrus oils, may constitute from 1.5
to 6.5 percent of the original oil.
Because of their flavoring qualities, citrus oils have been used
in a wide variety of products. Some of the industries in which
they are employed are: Perfume and toilet goods, beverages,
extract, baked goods, canning, condiment, confectionery, food
industry (general), ice cream, preserve, pharmaceutical, rectify-
ing and alcoholic beverage, and soap.

Nolte and co-workers (37) demonstrated in 1942 that it would
be economical to produce alcohol from citrus waste. However,
it was not until the short supply of cane molasses and the in-
creased demand for raw materials to produce ethyl alcohol dur-
ing World War II that citrus was utilized for this purpose.
During this period one plant which produces alcohol from citrus
molasses was constructed in Florida.
Citrus molasses is well suited for the production of alcohol
(C2HsOH), since it contains carbohydrates in a form which
permits direct fermentation by yeast.

General Processing Procedure
The manufacture of alcohol from citrus molasses consists of:
(1) weighing and mixing, (2) preparation of the pure yeast
culture, (3) addition of pure yeast culture, (4) fermentation
and (5) distillation.
Weighing and Mixing.-The molasses as received from citrus
molasses plants is stored in large steel storage tanks, each hold-
ing several thousand gallons. A measured or weighed amount
of molasses is pumped from the storage tanks directly into the

Type of Oil Coldpressed Steam
Fraser Pipkin
Method of Extraction All Pipkin Screw Brace Juice De-Oiler Oil
Methods Roll Press Extractor Extractor
Number of Samples Analyzed 35 4 8 6 17 9
Maxi- Mini- Maxi- Mini- Maxi- Mini- Maxi- I Mini- Maxi- Mini- Maxi- Mini-
mum mum mum mum mum mum mum I mum mum mum mum mum

Specific gravity 25C./25'C. .-.....--..----...- 0.8458 0.8416 0.8425 0.8420 0.8426 0.8416 0.8458 0.84411 0.8433 0.8420 0.8464 0.8400

Refractive index n 0 1.4734 1.4718 1.4722 1.4718 1.4724 1.4719 1.4734 1.4730 1.4729 1.4722 1.4732 1.4715
Refractive index of 10% distillate n D 1.47151 1.4703 1.4711 1.4708 1.4712 1.4707 1.4713 1.47031 1.4715 1.4707
Difference ......... ......... ................ 0.0031 0.0008 0.0013 0.00091 0.0015 0.0008 0.0031 0.0017 0.0015 0.0010
Optical rotation a 2 ..................... +97.76 +95.16 +97.76 +97.16 +97.59 +96.69 +96.30 +95.16 +97.57 +96.19 +98.56 +95.92

Optical rotation of 10% distillate oc 25 +98.70 +96.81 +98.19 +97.521 +98.32 +97.24 +98.70 +96.96 +97.89 +96.81
Difference .......... ... ......... ....... 2.44 0.00 0.85 1 0.011 0.73 0.03 2.44 1.51 1.30 0.00
Aldehyde content % .......................... 2.04 0.92 2.02 1.7 1.55 0.92 1.65 1.08 2.04 1.17 2.48 1.72
Ester content % ............................ 1.63 0.04 1.01 0.15 0.95 0.04 1.63 0.35 1.09 0.08 1.38 0.22
Evaporation residue % ...................... 4.93 1.07 1.57 1.07 2.20 1.38 4.93 3.12 2.59 1.85 1.24 0.08


Type of Oil Grapefruit Tangerine

Number of Samples Analyzed 6 9 1 1
Cold- Dis-
Coldpressed Distilled* pressed tilled

Maximum Minimum Maximum Minimum __

Specific gravity 25oC./25oC. ...................................- 0.8532 0.8508 0.8539 0.8415 0.8456 0.8407
Refractive index n .. 1.4761 1.4746 1.4746 1.4714 1.4734 1.4720
20 .
Refractive index of 10% distillate n ................. 1.4712 1.4698 1.4711
Difference .. ........... ............. ....... ..... 0.0054 0.0038 0.0023

Optical rotation cc D ......................... +9296 91.19 +96.50 +91.50 +91.18 +93.67

Optical rotation of 10% distillate ................................. +98.14 +95.81 +92.68
Difference ............. ...... ..... -..- ........... .............. 6.33 3.68 1.50

Aldehyde content % ...................... ..........-..-. -...... .... 1.67 1.49 4.06 2.30 1.08 1.24

Ester content % ............................. ........... 4.20 2.11 2.52 0.08 0.34 0.25

Evaporation residue % .......... ........... .. ...... ......... 8.02 6.02 3.66 0.19 4.53 0.20

Vacuum steam distilled (de-oiler oil).

Type of Oil Persian Lime Lemon

Number of Samples 6 5 1
Coldpressed Steam Distilled Distilled

Maximum Minimum Maximuml Minimum

Specific gravity 200C./20C. ................................................. 0.8823 0.8798 0.8579 0.8556 0.8555

Refractive index n ........ ............. .......... 1.4853 1.4842 1.4751 1.4743 1.4740
Refractive index of 10% distillate n ...... ......... ........ 1.4731 1.4729 ...
D -- - - - - - - - -
Difference ............... ...................... .. ........ ...... 0.0123 0.0112 ....
Optical rotation a ............................... 41.80 +38.60 +50.52 +46.84 +56.00
Optical rotation of 10% distillate cc 20 49.24 +47.60 .. .
Difference ........... .--.. .. --... -......-...........-.. ...... ... ................ 9.88 7.00 ...... ....

Aldehyde content % ... ................................... ...... ............... .... 5.52 3.66 2.71 1.61 1.19

Ester content % ....................................................... 8.20 7.42 3.49 2.41 2.45

Evaporation residue % ....................................... .................. 14.67 12.95 1.23 0.18 0.16


32 Florida Agricultural Experiment Stations

fermenter. The molasses is then diluted with enough water
to produce a solution or "mash" containing from 9 to 12 percent
sugar. The diluted molasses has a density of approximately
150 to 20 Brix. Since a high density molasses may have a low
fermentable sugar content, estimation of yield from density may
be misleading.
Pure Yeast Culture.-A pure yeast culture is propagated in
sterile mash under controlled temperature and air supply. From
this pure yeast portions are withdrawn for inoculation of larger
batches. The seed yeast used is a strain suitable for the fer-
mentation of citrus molasses and acclimatized for use under
slightly acid conditions.
Addition of Pure Yeast Culture.-After the molasses and
water have been thoroughly mixed approximately 5 percent by
volume of yeast is added. Inversion of the sugar is accomplished
by an enzyme, invertase, present in the yeast. Unlike some
alcohol processes the use of sulfuric. acid for inverting sugars
is not required when operating on citrus molasses. It is not
the practice to add a nutrient solution to the mash, since citrus
molasses contains enough yeast food to support the growth of
the yeast.
Fermentation.-Fermentation vats usually are constructed of
steel but may be made of any material that can be sterilized
easily. This is also true for yeast tanks. Of the sugars found
in citrus molasses, two-thirds are already inverted while one-
third, sucrose, is inverted into glucose and fructose by the in-
vertase in the yeast. The glucose and fructose are attacked by
zymase, the most important enzyme in the yeast, and are changed
into alcohol and carbon dioxide. The main reaction during fer-
mentation is:

C6H206 > 2CH50OH + 2C02
Other products formed are higher alcohols called fusel oil (pri-
marily iso-amyl alcohol), glycerin and a small quantity of or-
ganic acids.
Worthy of comment here is the fact that press liquor (100
to 140 Brix) from feed plants is not suitable as such for fer-
mentation. The 0.2 to 0.4 percent essential oil (peel oil) always
present in the press liquor will inhibit and slow up the
fermentation process. It therefore becomes necessary to con-
centrate the press liquor either completely or partially in order

Citrus By-Products of Florida 33

to lower the peel oil content to such a level that it will not inhibit
fermentation. The customary practice is to concentrate the
press liquor to citrus molasses by evaporation, effecting a com-
plete removal of the peel oil.
The fermentation of the molasses proceeds quite rapidly and
usually is complete within 48 hours. A short time after the
yeast has been added the evolution of carbon dioxide is apparent
and the quantity of gas evolved increases until the entire mash
appears to boil. In the first part of the fermentation the growth
of yeast is predominant, but as it proceeds the conversion of
glucose and fructose into alcohol is the major phenomenon.
Since the quantity of sugar required to produce one gallon of
alcohol is approximately 15 pounds, about 3 to 3.5 gallons of
citrus molasses (720 Brix-approximately 43 percent sugar) is
required to produce one gallon of alcohol.
The carbon dioxide gas from the fermenters is exhausted to
the atmosphere and lost. In some plants in other industries
this gas is collected, scrubbed with water to remove the alcohol
and passed through charcoal to remove any disagreeable odors
present. It is then either compressed into cylinders as liquid
carbon dioxide or made into a solid (dry ice).
Distillation.-The product of fermentation is a weak alcohol
solution containing from 5 to 7 percent alcohol by volume. It
is pumped through a continuous rectification process consisting
of a beer still with rectifying column, reflux condenser and a
cooler condenser to concentrate the alcohol.
The overhead vapors from the beer still, which contain ap-
proximately 50 percent alcohol, are passed to the rectifying
column while the residual "distillery solubles" are discharged
from the bottom of the still.
The purpose of the rectifying column is: (1) to separate the
last traces of low boiling impurities which are condensed and
cooled by the condenser and returned to the top of the column,
(2) to separate high boiling impurities called fusel oil, and (3)
to concentrate the finished alcohol to 95 to 96 percent (190 to
192 proof). The final product is removed continuously from
the top of the column through a cooler to the purified alcohol
storage tanks.
The crude fusel oils are withdrawn at the point of maximum
concentration in the rectifying column and passed to a batch still
where they are purified.

34 Florida Agricultural Experiment Stations

The "distillery solubles" discharged from the bottom of the
beer still are free of alcohol and are usually discharged to dis-
posal pits. Since "distillery solubles" are known to have food
value, an effort was made at one time to incorporate them with
citrus molasses for feed use. This combination later was aban-
doned because it seriously increased the viscosity and decreased
the overall sugar content. As concentrated "distillery solubles"
from blackstrap molasses are sometimes used to emulsify and
stabilize Vitamin A and D concentrates in mixed feeds, the
residue from citrus alcohol plants possibly could be used in a
similar manner.
All distillation equipment is fitted with locked valves and
seals so that liquids cannot be admitted or withdrawn except
in the presence of an Internal Revenue officer.

Utilization of Citrus Alcohol
Ethyl alcohol made from citrus is, of course, identical with
that made from such products as grain and cane molasses, and
can be put to similar uses. Whether alcohol made from citrus
can compete with that from other sources depends on various
economic factors.

Although citrus press liquor is normally concentrated to
citrus molasses, it can be used advantageously also in the pro-
duction of feed yeast. Yeast has considerable value as a feed
supplement, since it is one of the richest natural sources of the
B vitamins and contains about 50 percent protein. Nolte and
co-workers (37) were among the first to investigate the possi-
bility of fermenting citrus press liquor to feed yeast and alcohol.
Torula utilis, a wild, fast growing yeast, was selected because
it propagated rapidly and produced little alcohol. This organism
further appeared to give the best yeast yield of the five tested.
Since the press liquor contained insufficient nitrogen and phos-
phates for optimum growth, it was necessary to add nutrient
salts. The workers obtained from a liquor containing 1 percent
total sugars yields ranging from 44 to 48 percent dry yeast by
batch operation, based on the total sugar content of the press
liquor. Diluted press liquor containing not more than 1 per-
cent total sugars produced higher yeast yields and faster propa-

Citrus By-Products of Florida 35

Veldhuis and Gordon (49) later were able to adapt to citrus
liquors a continuous method of conducting the fermentation de-
veloped originally for the utilization and disposal of liquors
obtained during the manufacture of starch from sweet potatoes.
A schematic diagram of the continuous processing procedure
(49) which gives the most successful results is shown in Fig. 1.
General Processing Procedure
Citrus press liquor from the continuous presses of a feed mill
is first passed through an 80-mesh shaker screen to remove the
larger particles. The suspended insolubles remaining are not
considered objectionable in the final feed yeast. A preheater
raises the press liquor temperature to 1400F. to prevent its pre-
mature fermentation while held in a large storage tank. The
liquor is pumped from the storage tank through a pasteurizer,
operating at 2000F., and then cooled to approximately room
temperature in a heat exchanger prior to entering the yeast
propagators. Once the culture is firmly established and the
propagator in continuous use, pasteurization can be eliminated,
since Torula utilis apparently can outgrow the other micro-
organisms present. A concentrated nutrient solution of am-
monium sulfate and tri-sodium phosphate is fed continuously
to the yeast propagator in proportion to the feed rate of press
liquor. Other necessary nutrients are supplied by citrus press
liquor. A pH between 4 and 5 must be maintained for most
favorable yeast growth by the addition of either the nutrient
solution or ammonia. Since the fermentation generates con-
siderable heat, cooling coils are fitted in the bottom of the yeast
propagator to maintain a constant temperature of approximately
960F. Porous aeration tubes fitted in the bottom of the propa-
gator supply a continuous flow of air to maintain rapid yeast
growth. The function of the air is to inhibit fermentation and
increase respiration, agitate the medium, remove toxic end
products, and stimulate vegetative growth. Anywhere from
500 to 1,200 cubic feet of air is necessary to produce a pound
of yeast. The citrus press liquor moves continuously through
the propagator so that in a single-stage plant the total detention
time is only about three hours. The propagator discharges a
yeast suspension to a collecting tank, after which a continuous
centrifuge concentrates the yeast to a thick slurry of about
10 to 15 percent solids. This slurry is then dried by either a
drum or spray drier.

36 Florida Agricultural Experiment Stations

Utilization and Composition

The spent liquor from the continuous centrifuges is discharged
as a waste product. By this time the biological oxygen demand
has been reduced 80 percent. Ninety-five percent of the sugars
and about 65 percent of the total organic matter have been
utilized. Veldhuis and Gordon (49) were able to obtain 60-percent
yields when press liquor was diluted with two volumes of water
and 33-percent yields with full strength press liquor. This is the
equivalent of 20 to 36 pounds of feed yeast per 1,000 pounds of
100 Brix press liquor processed. The average composition of
feed yeast from press liquor (Table 9) was compiled by Nolte
and co-workers (37), who analyzed a composite of 10 samples.


Dry Yeast Percent Ash Percent

Moisture .................-.... 1.29 Phosphorus pentoxide ...........--- .. 45.75
Protein (N x 6.25) .- 55.28 Magnesium oxide .-----.......... 4.95
Crude fat .................... 4.51 Calcium oxide .........---.............. .. 1.26
Glycogen ..................... 12.78 Silicon dioxide ........................... 2.58
Cellulose, gum, etc..... 18.06 ISulfur trioxide ......................... 7.79
Ash -..----.....- .----. 8.08 Chlorine --- ---- .............. 0.22
Iron oxide ..--.....--- -------------........ --- 0.40
Sodium and potassium oxides.. 37.05

Significant quantities of thiamin, riboflavin, ergosterol, niacin
and pantothenic acid also are present in the yeast.
No citrus processor at present is making feed yeast, since the
economics seem to favor diversion of press liquor for production
of citrus molasses. However, the process possibly could be used
advantageously in the disposal of the more dilute waste liquors
found in a citrus cannery because liquors of low sugar content
can be utilized effectively.
Although feed yeast has achieved importance as a high pro-
tein feed for animals, it can be refined and made more palatable
for human consumption. Since it is the richest natural source of
biologically complete proteins and a rich source of a pellagra-
preventing factor, it has many beneficial medical uses. In Ger-
many during World Wars I and II it was recognized as an ex-
cellent source of essential nutrients and was used extensively in
the preparation of their "ersatz" foods.

Citrus By-Products of Florida 37

The production of citrus seed oil has steadily grown from 45
tons during the 1938-39 season (36) to an estimated yearly
production of 500 tons. Although the manufacture of citrus
seed oil has been of minor importance in the citrus industry,
it seems to be a well established small enterprise at present.
The production of citrus seed oil seems to be highly desirable,
since it provides a more profitable outlet for the seeds than does
processing into dried citrus pulp. Obviously, only seedy varieties
of citrus are suitable.
According to Fudge (15) average yield of wet seeds from
seedy varieties of grapefruit amounts to about 2 to 2.5 percent,
based on weight of the whole fruit. Since the quantity (45) of
seedy grapefruit processed in Florida during the 1949-50 season
amounted to approximately 9.5 million boxes (85 pounds fruit
per box), the potential yield of wet seeds would then be about
9,000 tons. From this quantity of seeds a calculated yield of
1,350 tons of oil could be produced. Calculated yields are prem-
ised on the basis that wet seeds contain 50 percent moisture
and dried seeds contain 30 percent oil. During this same period
(45) 20 million boxes (90 pounds fruit per box) of mid-season
oranges, containing about 4 percent seeds on a whole-fruit basis,
were processed. The potential yield of wet seeds would then
be about 36,000 tons and from this quantity a calculated yield
of 5,400 tons of oil could be produced. The total potential of
seed oil would then be about 6,750 tons. Because only a few of
the seeds available are utilized, the quantity of oil produced is
considerably less.
Presently there is one plant in Florida which specializes solely
in the production of oil from citrus seeds. However, a good
many processing plants collect and dry seeds, then ship them
to an extraction plant for removal of the oil. Many investigators
(1, 12, 13, 22, 27, 47) have determined the physical and chemi-
cal properties of these oils, showing their possible commercial use.

General Processing Procedure
The seeds are obtained usually from two sources: (1) residue
from single strength and concentrate juice plants, consisting
of peel, seed, rag and pulp, and (2) the residue from sectioniz-
ing plants, which consists of only seed, rag and pulp. A schematic
diagram of the processing procedure for the manufacture of

38 Florida Agricultural Experiment Stations

citrus seed oil is shown in Fig. 1. Seeds are separated from
the peel, rag and pulp by passing the residue first through a
coarse rotary screen which removes the peel, then through a
screen with smaller openings where the rag and pulp are washed
through by press liquor sprays. The peel discharged from the
first screen is combined with the rag and pulp from the second
screen and sent to the pulp plant to be processed into cattle
feed and molasses. Seeds discharged from the second screen
are dried to a moisture content of 8 to 10 percent in either
direct, steam-tube or indirect fired drier. The dried seeds are
then conveyed to storage bins and removed as desired for pro-
cessing. This process consists of passing the dried seeds through
a roller mill (Fig. 14) where they are flaked, then over a screen
to remove the hulls and finally through an expeller (Fig. 15),
where part of the oil is removed by pressing. The pressing
operation may be done either hot or cold. A combination of
both cold and hot pressing is sometimes used, according to the
purpose for which the oil is being prepared. Coldpressed oil
is considered the highest grade, while hot pressed oil is a tech-
nical grade.
Solvent Extraction.-After the seeds have been pressed to
remove part of the oil they are finished usually by solvent ex-
traction. The equipment used most commonly is a multiple
effect, counter-current, batch type, consisting of several extrac-
tion kettles. Continuous solvent extraction, such as has been
employed successfully for the processing of soybeans, also can
be adapted to extraction of citrus seed.
Two continuous extraction systems are widely used. In the
first a chain of baskets which have perforated bottoms and re-
semble a bucket elevator is used. Solvent is sprayed upon the
flakes and percolates through them as it runs downward from
basket to basket. In the second system the flaked seeds or
residues from the expeller move slowly through a vertical U-tube
by internal screw conveyors counter-currently to a solvent for
the oil.
None of the common distillation methods have been found
suitable for recovering or refining citrus seed oil.
Refining.-Unrefined oil collected in holding tanks has a red-
dish color, a pleasant aroma and an extremely bitter taste.
The oil is refined by mixing it with a calculated amount of
caustic soda solution. This forms an emulsion which breaks

f .. *.. :.,- '.' .' .'. b .'d. .' / .

I 1/ --"-...' '.-.

Fig. 14.-Roller mill. (Photograph courtesy Davidson-Kennedy Co.,

40 Florida Agricultural Experiment Stations

when the mixture is heated gently to 50C. for 10 to 15 minutes
with mild agitation. The precipitated soap stock is allowed to
settle, then is separated by filtration. The oil is then washed
and heated to 110'C. to remove the last traces of moisture.
The caustic treatment neutralizes free fatty acids and removes
bitterness. The oil may be further refined by adding activated
carbon and filter cel, then filtering.

Fig. 15.-Anderson expeller. (Photograph courtesy V. H. Anderson Co.,
Cleveland, Ohio.)

I --mom

---------------- --------_

Citrus By-Products of Florida 41

Typical Analyses for Citrus Seed Oils, Meal and Hulls

Citrus seed oil is a mixture of fatty acids esterified with gly-
cerol, similar to peanut and cottonseed oil. In citrus seed oil,
as well as many similar oils, the number of fatty acids occurring
may vary from 6 to 10. Most of the various fatty acids can be
divided into three classifications: (1) saturated; (2) unsaturated,
lacking two hydrogen atoms; and (3) more unsaturated, lack-
ing four or more hydrogen atoms. The specific fatty acids found
in grapefruit seed oil are shown in Table 10.


Components Percent

Oleic ............ ............. .... ......... ...........-- ..- ..-....-... 20.5
Linoleic ....--..................................................... .......... 51.0
Palm itic ................................... ..... .. ... .... .... -20.1
Stearic .................................. .......................... .... 7.6
Lignoceric ..............--- ........................... .......... .... 0.1
Unsaponifiable acid .................... ....-..-...........-.. 0.7

Table 11 gives the physical properties for bleached and win-
tered grapefruit oil. The bleached oil was obtained by decoloriz-
ing the refined oil with 0.5 percent decolorizing charcoal and 2.0
percent of a filtering aid. The wintered oil was secured by cool-
ing the refined and bleached oil to 1IC. and then pressing the
oil from the solid stearin by means of a hand press.
Data presented in Table 12 show that the characteristics of
grapefruit, orange and tangerine seed oils are very similar.


Property Bleached Wintered

Specific gravity 25oC./25C. ............................ 0.9179 0.9199
Refractive index N 25 1.4688 1.4700
D value- ---------------------- 7 0.26
A cid value ................. ............... ..................... 0.17 0.26
Saponification value .................... -................ 197.5 192.2
Iodine no. (Hanus) ........................................ 101.7 109.2
Unsaponifiable matter, % ............................... 0.38


Grapefruit Seed Oil Orange Seed Oil Tangerine Seed Oil
Analysis II
I I] Coldpressed Solvent-extracted
(36)* (23)* (48)* (23)* (47)* (47)*

Specific gravity 250C./25"C..... 0.91970.9153 0.921-0.9251-. 0.9168 0.9165
Refractive index N 25C...... 1.4698 1.4700 1.4686 1.4638-1.4647400 1.4698 1.4702
Acid value ........................ ... 0.95 2.5I I 4.83 4.31
Saponification value .................. 193.0 194.1 197.5 194-197 193.78 193.55
Unsaponifiable matter, % ........ 0.48 0.7 0.95 0.34 0.54
Iodine value ............ .............. 100.9 (H) 106.3 (H) 101.7 (W) 98-104 107.4 (W) 107.3 (W)
Thiocyanogen value ................. 66.22 66.37
Acetyl value .......... ........ ........... 2.4 7.7 8.2

Reference to literature cited.
W = Wijs.
H = Hanus.

Citrus By-Products of Florida 43

The compositions of whole air-dried grapefruit seeds and air-
dried hulls are given in Table 13.


Components Seeds Hulls

Moisture ........ ............................ ...... 11.86 10.19
Crude fat (ether ext.) .............................. ...... 30.30 1.17
Protein (N x 6.25) ............................................... 15.94 4.00
Crude fiber ...................................... ................... 9.14 39.75
A sh ........................................................................ 2.48 2.97
Cellulose (Cross & Bevan) .................................. 32.50
Pentosans .. ................................................ 16.34
N-free extract (by difference) ............-.............- 30.28
SiOs ............. ........... ....... .. ...-. ..............--........----. 0.28
Fe + Al (Fe.Oa + A103.) .................................. 0.50
Ca ----...-..... ---..-.... -------......... ..... -........ .. .. 0.36
Phosphates ....................... ............... ................ 0.56
Na ..................................... .... ............. i 0.052
K .... .... ...... ................... .............................. 0.54

Residue from seeds that have been pressed to remove oil is
called press cake. Composition of the press cake obtained from
grapefruit seeds with and without hulls is shown in Table 14.
The residual oil content of the press cake is sufficiently high to
warrant its extraction by solvents and its recovery by this
method has been practiced for the past two years.

Seed Press Cake Seed Meal
Components I with Hulls Without Hulls
(36) (14)

percent percent
Moisture .......................-- ... ----.............---- 3.43 15.0
A sh ................................... ---..... ---.... 4.04 6.0
N as N H3 .................................. ...... 4.21
N as protein ....-........................------------ ....21.60 33.9
Crude fat (ether ext.) ........... ---.............. 13.95 5.7
Crude fiber .............................................. 26.50 7.4
SiO ---..... -..---..-................- .......-- ............ 0.081
S ---........... ............... ... ..............---- .. 0.088
C a ................................................. ......... 0.35
M g (M gO ) ................................................ 0.39
NaC1 KC1 ................. .......................... 2.48
Phosphates (P2sO ) ................................... 0.55
F e .............. ..... .......... .. ..............-..... 0.0014

44 Florida Agricultural Experiment Stations

Utilization of Citrus Seed Oils, Meal and Hulls
The flavor of a highly refined citrus seed oil resembles that
of olive oil, for which it sometimes has been substituted. It is
pale yellow in color and is considered wholesome and well suited
for food. It has been used after hydrogenation in the manu-
facture of butter substitutes and, in some instances, in the
production of a cooking fat. The lower grades of citrus seed
oil are used in the manufacture of soap and in the preparation
of sulfonated oils for the textile industry.
A brominated seed oil of high density (approximately 1.30)
has been produced for use in the beverage industry. The density
of the flavoring oil is adjusted to that of the drink by addition
of brominated oil, thus preventing ring formation around the
top of the bottled beverage.
The press cake or seed meal usually is broken up and blended
with dried citrus pulp and sold as cattle feed. This is desirable,
since the meal is high in protein and fat content, both of which
are essential in the diets of animals. Glasscock et al. (16)
demonstrated that citrus seed meal was as valuable as cotton-
seed meal in meeting the protein requirements of growing and
fattening steers, but was harmful to swine when fed at levels
as low as 10 percent of the total ration. The meal has been
used to some extent as a poultry feed. However, before it can
be fed to poultry it must first be solvent-extracted to remove
limonin, the bitter principle present in the seed (14).
The hulls are usually sold to fertilizer plants as a conditioner
for fertilizer.

Each year approximately 20 million pounds of sugar are pur-
chased by the citrus industry of Florida to sweeten single-
strength citrus juices and canned grapefruit sections. Of this
quantity, over half is used as a 400 to 50' Brix syrup in packing
sections. At present, this syrup is made by dissolving in a
blending tank mixtures of sucrose and dextrose in water. A
similarly sweet syrup can be made from citrus waste liquors
by methods that may show economical advantages over the
purchase of raw sugar. Since the sugars found in citrus are
always partially inverted, there seems to be very little chance
of ever making a crystallized sugar. However, liquid sugar
solutions are easier to handle and are more in demand today.

Citrus By-Products of Florida 45

The production of bland syrup is premised on the use of ion
exchange resins that have the capacity of removing, by ex-
change adsorption, the citric acid, minerals and other impurities
present in citrus juices. The dilute pure sugar solution thus
obtained is then concentrated by conventional methods to the
desired Brix.
The application of ion exchange resins has been investigated
more thoroughly for demineralizing cane syrups, beet syrups
and molasses for increased yields of raw sugar. However, three
citrus processing plants in Florida have, at various times, in-
vestigated ion exchange resins in pilot plant or moderate-scale
plant equipment. Since the process requires considerable tech-
nical skill, as well as a large initial investment, its development
has been slow. By persistent effort, one plant has applied the
process to advantage.
In manufacturing citrus bland syrup, citrus press liquor
should not be considered as the only source material for its
production. Juice from excess citrus fruit not suitable for
production of concentrates or single-strength juice could be used.
Since citrus juices have a higher sugar purity and fewer im-
purities than peel liquor, the process can be shortened consider-
ably and simplified by their use. Over-mature tangerines are
especially suited, since tangerine juice tends to be very sweet
and has a minimum of citric acid. With orange and grapefruit
juices and orange and grapefruit peel press liquor the problem
becomes successively more difficult. This is accounted for by
two factors. All citrus fruits appear to have a bitter glucoside
present, hesperidin in the case of oranges and tangerines and
naringin in grapefruit, which is both bitter and difficult to re-
move. The bitterness of naringin is quite pronounced and ap-
parently is more difficult to remove than that attributable to
hesperidin. The quantity of glucosides is much higher in peel
press liquors than in the citrus juice, due to the lime addition
which increases the glucoside solubility. Gore (17) was able to
take strained orange juice, treat it with 5 percent of an anion
exchange resin and produce, after filtering and concentrating,
a clear, well flavored and well colored syrup. The syrup from
grapefruit juice similarly prepared possessed a bitter taste.

General Processing Procedure
Since the manufacture of bland syrup from citrus press liquor
is most difficult, it will be described with the knowledge that

46 Florida Agricultural Experiment Stations

certain steps can be avoided by using juices of higher purity.
The process is broken down conveniently into the operations
shown in Fig. 1: clarification, ion exchange purification, decolor-
ization, and concentration.
Clarification.-Citrus press liquor is a yellowish, cloudy liquor
with approximately 1 percent insoluble solids, part of which
may be removed by shaker screens. Further clarification by
filtration is decidedly uneconomical because of the slimy char-
acter of the insolubles. One pilot plant, however, was able to
clarify the liquor satisfactorily by two-stage centrifugation. A
basket centrifuge was used in the first stage, followed by a
super centrifuge that polishes the liquor after passing through
the first cationic exchange bed. An investigation by Hendrick-
son (20) showed that clarification of citrus press liquor was
best effected by sedimentation wherein the peel oil was first
distilled off, since it tended to buoy the suspended matter. Dis-
tillation also sterilizes the liquor, thereby decreasing the possi-
bility of large sugar losses due to bacterial infection in the upper
layers of the cation exchange bed. Some investigators claim,
however, that any heating prior to demineralization and decolor-
ization tends to set the color and make it more difficult to remove.
Every precaution should be taken to prevent caramelization of
sugars or any coloring of the liquor while processing it.
Ion Exchange Purification.-Basically, demineralizing and
purifying sugar solutions consist of two steps. First, a cationic
exchanger removes the dissociated positive ions such as K+,
Ca++, and Mg++ from the liquor by replacing them with hy-
drogen ions. The corresponding acids-hydrochloric, sulfuric
and citric-that are formed from the salts in solution are then
brought in contact with an anionic exchanger, where the entire
acid molecule is adsorbed. The reactions are reversible and when
an exchanger has reached a pre-determined saturation level, it
can be regenerated and re-used. Ion exchange resins may be
used batch-wise or in columns, each method having certain ad-
vantages. However, it is more convenient to use column oper-
ation when dealing with large volumes of citrus press liquor.
Citrus press liquor which has been heated must be cooled
below 120 F. prior to entering the first cationic exchanger,
although some resins can withstand much higher temperatures.
A flow rate of approximately two gallons per minute per cubic
foot of resin in the exchange bed is maintained. The press

Citrus By-Products of Florida 47

liquor is passed continually through the cationic bed until the
effluent analyzes too high a percent of some one tracer ion, such
as iron. Downflow operation through the exchanger is used,
since it gives better performance throughout the run and a
sharper end point.
The highly acid effluent subsequently is passed through the
anion exchanger in downward flow at approximately the same
rate. The equipment used must be designed to withstand the
corrosive influence of highly acid and alkaline conditions. For
this reason, the exchangers are rubber lined and have connect-
ing lines of hard rubber. The use of a conductivity meter, such
as a Solu-Bridge, is very effective in determining the purity of
the effluent from the anion exchanger. One plant found it
necessary when processing citrus press liquor to use two sets
of exchangers to obtain a product of satisfactory purity. One
set was always maintained in a highly regenerated condition to
remove last traces of impurities better, especially the bitter
glucosides, naringin and hesperidin. For the most economical
operation the size of the cation exchanger should be in proper
relation to the anion exchanger, so that both will pass equal
quantities of citrus press liquor before regeneration is required.
Some large sugar refineries have numerous batteries of ex-
changers, so that at any one time one set is in the process of
being regenerated and washed while the other set is on flow.
Decolorization.-A granular carbon bed is interposed between
the first cationic and anionic exchanger. Practically any waste
vegetable material such as seaweed, peet, bagasse, press cake,
rice hulls or sawdust can be used as the basis for a decolorizing
carbon. The carbon removes much of the coloring matter as
well as organic and inorganic impurities. Activated carbons can
be used and they serve the important function of also removing
the bitter glucosides. Since it is difficult to remove the last
traces of bitterness from it, treated citrus press liquor often
must be put through an activated carbon bed again after pass-
ing the second anion exchanger. The use of activated carbon for
adsorbing naringin has been patented recently by Burdick and
Maurer (8), who found the optimum pH to be 5.5 and tempera-
ture 570C.
Concentration.-The sweet dilute, effluent is concentrated to
75 to 850 Brix in conventional multiple-effect evaporators.
Care must be taken to avoid any caramelization during this
process, since the final product should be as near water-white as

48 Florida Agricultural Experiment Stations

possible. It should be mentioned, however, that citrus bland
syrup has a tendency to darken in storage, probably because of
the incomplete removal of nitrogen compounds.

The pectic substances in citrus peel are believed to be inti-
mately associated with cellulose, either in the outer cell walls
(46) or between each of adjacent cellulose walls of the cells.
It is usually most abundant in immature fruit as protopectin,
which can be liberated as soluble pectin by various enzymatic and
chemical methods. Citrus peel is a rich source of pectin, the
amount varying with season and variety. As the season pro-
gresses the jelly units of pectin in the peel diminish and the
quantity of insoluble protopectin decreases.
Since pectin is not a pure substance, its evaluation depends
largely on the molecular size of the pectic substance, degree of
esterification, amount of accompanying ballast material and
method of manufacture. The gelling power and viscosity of
pectin solutions depends on the number of galacturonic acid
units strung together to form each molecule, for the larger the
molecular size the higher the jelly strength. The degree of
polymerization is dependent upon the extraction method. It is
common to speak of pectin as having a certain grade, which
refers to the number of pounds of sugar that can be gelled by
one pound of the pectin in accordance with a standard method.
Another term used conveniently is the jelly unit, obtained by
multiplying together the percent yield and jelly grade of the
Although all citrus peels contain comparatively large quan-
tities of pectin, lemon and grapefruit are most suitable for its
extraction. In Florida, the production of pectin has been limited
mostly to dried citrus pomance, a crude product bought by jam
and jelly manufacturers, from which pectin is extracted by
means of hot acid solutions. Approximately half the pectin
manufactured in the United States is derived from citrus (mostly
lemons). The production of a refined high grade pectin involves
considerable know-how and experience, as well as a large capital
investment for equipment. For this reason, as well as economic
considerations, pectin production in Florida has developed slowly.

General Processing Procedure
Methods of isolating pectin from citrus fruits are numerous.

Citrus By-Products of Florida 49

However, its manufacture can be broken down into four opera-
tions: leaching, extraction, clarification and isolation.
Leaching.-The accumulated canning residue, consisting of
peel, rag and seeds, is the raw material used. It is important
that this be processed without undue delay, so that the enzymes
present may be inactivated (by heat) and the degradation of
the pectin thereby prevented. The enzymes, protopectinase,
pectinase and pectase are catalysts which cause the breakdown
of pectin and seriously decrease the jelly units obtained per
batch. The seeds and rag are removed by passing the cannery
residue through a rotary screen with one-inch openings. Fine
water jets located inside the screen aid this separation. The
peel is conveyed to a temporary storage point and withdrawn
at intervals as required for leaching. Just prior to entering
the leach tank the peel is cut into pieces varying in size from
1/8 to 1/4 inch. A weighed quantity of chopped peel is dropped
from an overhead hopper into a false bottom leach tank fitted
with an agitator and containing boiling water. The mass is
agitated continuously to aid the leaching, and live steam is ad-
mitted to raise and maintain the temperature at 900C. for five
minutes. An equal quantity of cold water is added to reduce
the temperature quickly from 90C. to 60C., then the tank is
drained immediately. Two further leachings of short duration
are made with cold water. They serve to remove most of the
remaining soluble constituents, such as sugars, acids and min-
erals, which are considered contaminants. Some soluble pectin
also is removed by this operation but the loss is of little sig-
nificane, since it is of low grade. A hydraulic press squeezes the
leached peel, releasing further traces of soluble impurities. The
leached and pressed peel is now ready for extraction; or if de-
desired, it may be dried in steam-tube rotary driers and stored
in silos for subsequent use. Low temperature controlled trying
is necessary to prevent excessive loss of grade. This dried
product, containing 5 to 10 percent pectin, is commonly called
pectin pomace and has been used for the manufacture of jams
and marmalades.
Extraction.-The leached and pressed peel is conveyed into
a tank fitted with a steam coil and agitator where the insoluble
protopectin is converted to soluble pectin by acid hydrolysis.
Conversion is carried out at a pH of approximately 2.4 over
a one-hour period at approximately 90C. The mass is agitated
continuously during the extration. Either hydrochloric or lactic

50 Florida Agricultural Experiment Stations

acid can be used, but the entire operation must be controlled
carefully since destructive hydrolytic action on the pectin itself
is possible.
Extraction can be carried out with other acids also, both
mineral and organic. Although the fundamental extraction con-
ditions are not necessarily the same for all varieties of citrus
fruit, Myers and Baker (33, 34) were able to determine the
optimum pH, temperature and holding time of lemon albedo for
both maximum yield and maximum jelly units. One process
patented by Myers and Rouse (31) avoids the use of acid by
adding a cationic exchange resin that adsorbs sufficient cations
from the extraction solution to lower the pH to the proper ex-
tent. Although the exchange resin must be recovered later,
this process has the advantage of decreased ash, simplification
of isolation procedure, higher yields of high grade pectin at
higher pH readings, removal of toxic heavy metals, lower vis-
cosity at higher concentrations and lower chemical costs. As
the pectin dissolves in the acid solution it becomes more and
more viscous. Sufficient water, therefore, is added to the ex-
traction tank to provide a relatively dilute pectin solution (0.5
to 0.7 percent). This dilution further aids in dissolving the
higher grade pectin, which is increasingly insoluble. After one
hour at 900C. the contents of the extraction tank are cooled
quickly to 600C. by circulating cold water through the steam
coils and the solution is then ready for clarification.
Clarification.-The dilute viscous pectin solution and insoluble
pulp are pumped to a basket centrifuge where a considerable
quantity of the pulp is removed. The centrifuge effluent is col-
lected in a clarifying tank and processed in accordance with its
ultimate use. When manufacturing low methoxyl pectin it is
convenient to de-esterify the pectin solution at this point. Three
methods are generally available for partially demethylating pec-
tin: (1) acid hydrolysis wherein the pH is decreased by adding
hydrochloric acid, (2) enzyme hydrolysis by pectase of tomato
origin and (3) mild saponification with ammonia at much re-
duced temperatures. Since the last two methods are rapid they
have found commercial application. However, care must be
taken to inactivate the enzyme, or neutralize before the reaction
proceeds too far. Further purification and decoloring is accom-
plished by stirring the pectin solution with activated carbon for
20 to 30 minutes at 55 to 60C. After a small quantity of filter

Citrus By-Products of Florida 51

aid is added the pectin solution is filtered through a precoated
plate and frame filter press and is ready for isolation.
Isolation.-The isolation of pectin from its solution can be
accomplished by numerous methods, but it is advantageous first
to concentrate the clear dilute pectin solution in multiple-effect
evaporators under reduced pressure. The pectin solution is con-
centrated as much as its viscosity will conveniently allow and
sent to a blending tank where the pH is adjusted to 3.5 with
ammonia or soda ash, depending on ash specifications. Sugar
is added to standardize the grade whereupon the 4 to 6.5 percent
pectin solution can either be sterilized and sold as a liquid or
dried by a rotary drum or spray drier.
Another process requiring considerably more skill depends
on precipitating the pectin at an adjusted pH with an aluminum
salt and ammonium hydroxide, skimming, pressing and vacuum-
drying the product. It is refined further by washing with acid
alcohol and then plain alcohol to remove the last trace of acid and
aluminum. The product is vacuum dried again. Dried pectin
can be obtained as either a flake or a powder, depending on the
drying technique used. However, the dried product usually is
micropulverized and marketed as a very fine powder.

Utilization of Citrus Pectin
Jellies, jams and marmalades in their various forms are prob-
ably the first products which utilized pectin. However, it was
not recognized until some 25 years ago that pectin alone was
not sufficient for the manufacture of gels. It has since been
found that the presence of pectin, sugar and acid in the proper
proportions are necessary for the manufacture of jelly products.
Today the preserve industry is still the largest single outlet for
this substance. Continued research has developed new applica-
tions for pectin, considerably increasing its use.
Confectionery.-The shortage of critical supplies in the candy
industry (18) has resulted in a stimulated research program
to develop new products in order to maintain volume production.
Among those products developed are modified pectins obtained
by partial de-esterification, referred to as low-methoxyl pectins.
This type pectin is used to produce low-sugar-content candies as
well as to develop new types of candies. Low-methoxyl pectins
depend upon a reaction with a metallic ion, such as calcium, to
form gels, rather than an acid and a high concentration of sugar.

52 Florida Agricultural Experiment Stations

The pectins have been used to make jellies, pectin jelly candies,
cream-center-type candies, and to form protective coatings or
glazing agents for candies.
Meat Packing.-Pectinate films (43) used in the meat pack-
ing industry, such as casings on sausages, ham and other pro-
cessed meats, are applied by dip coating. The process is simple,
since the meat is molded into the desired shape and then dipped
in a dispersion of calcium sodium pectinate. The gel coating
is dried and the resulting film forms an attractive casing.
Food Industry.-Pectin is used in the food industry for a
variety of products. Films of the calcium sodium pectinate type
and others made with different cations offer possibilities in pre-
serving frozen foods, cheese, fish, etc., and as an anti-sticking
or glazing agent for dried or candied fruits. It is also used in
salad dressings, catsup, table sauces, mayonnaise, puddings and
in ice creams as a stabilizer.
Pharmaceutical.-Pectin possesses a multitude of properties
which have potential value in the medicinal field. Numerous
contributions on the use of apples for the treatment of gastro-
intestinal disturbances have been made. Malyoth (28) suggested
that the efficacy of raw apples was due to its pectin content.
Winters and Tompkins (50), in controlled experiments, observed
that pectin-agar in a mixture of dextrimaltose is far more effec-
tive than scraped raw apples in the treatment of infant diarrhea.
Pectin, when combined with metals, forms compounds referred
to as pectinates. Myers and Rouse (32) discuss one of these
compounds, nickel pectinate, and show that clinical evidence has
demonstrated its value in the treatment of acute and chronic
bacillary dysentry, acute ulcerative colitis and infected wounds.
Pectinates of nickel, cobalt, manganese, lead, zinc, copper, cal-
cium and silver have been discussed by Arnold (2) and their
bactericidal action shown.
Calcium pectinate films may be used in surgical dressings in
the manner of celluronic acid gauzes. Pharmaceutical pastes
and ointments can be stabilized with pectin and various medi-
cants incorporated in it.
Miscellaneous.-The fire-retardant properties of metallic pecti-
nates make them useful in film-coating preparations for use on
flammable surfaces or as films for use as decorations or draperies.
Pectin can be used as an emulsifier for various oils, such as
essential oils, castor oil, mineral oil, cottonseed oil and olive

Citrus By-Products of Florida 53

oil, and for tree-spray preparations. Glue and mucilages also
are made of pectin. Citrus pectin and pectates have been used
as creaming agents for liquid latex, as well as for hardening


Each of the products described in the preceding pages either
has been manufactured in pilot plant equipment or is presently
in full scale production. Other products not manufactured now
but with possibilities worthy of development are: lactic acid
by fermentation of citrus press liquor with lactobacilli; anti-
biotics and other fermentation products, using citrus waste
liquors as the substratum; the bitter glucosides, naringin and
hesperidin, by alkaline extraction and acid crystallization; citric
acid from either evaporator scale or from precipitated and settled
insolubles in the hot sedimentation of citrus press liquor; ascor-
bic and citric acids in the regenerating effluent of anion ion
exchange resins; methane by fermentation of the more dilute
waste liquors; and the waxes recovered by polishing winterized
peel oils. Still further possibilities are the recovery of vitamin
P and inosital. All of this leads to the inevitable conclusion
that citrus waste residues possess a wealth of raw materials
and should be considered a most valuable asset to the citrus

Acknowledgments are made to the following commercial processors and
manufacturers in Florida, whose earnest cooperation contributed much
to the success of this work: Juice Industries, Inc., Dunedin; Florida Citrus
Canners Cooperative, Lake Wales; Kuder Citrus Pulp Company, Lake
Alfred; Munsco Mills, Inc., Fort Pierce; Pasco Packing Company, Dade
City; Plymouth Citrus Growers Association, Plymouth; Suni-Citrus
Products Company, Haines City; Southern Fruit Distributors, Orlando;
Winter Garden Citrus Products Cooperative, Winter Garden; Bruce's
Juices, Inc., Tampa; Minute Maid Corporation, Plymouth; Lake County
Canners, Inc., Eustis; Adams Packing Association, Inc., Auburndale;
J. William Horsey Corporation, Plant City; Libby, McNeil & Libby,
Ocala; California Packing Corporation, Tampa; Snow Crop Marketers
Division, Clinton Foods, Inc., New York; David Bilgore & Company, Clear-
water; Consolidated Citrus Products Company, Tampa; Florida Citrus Oil
Company, Bartow; Essential Oil Producers, Inc., Dunedin; Fraser-Brace
Engineering Company, New York; Hutchman Seed Oil Company, Lakeland;
Feed Products, Inc., Groveland; and Polk Packing Association, Winter
Haven. The authors are especially indebted to A. H. Rouse for his in-
valuable help and knowledge on pectin procedures.

54 Florida Agricultural Experiment Stations


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Food Ind. 17: 1479-1483. 1945.

Citrus By-Products of Florida 55

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56 Florida Agricultural Experiment Stations

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