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Group Title: Bulletin University of Florida. Agricultural Experiment Station
Title: Citrus vinegar
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Permanent Link: http://ufdc.ufl.edu/UF00027160/00001
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Title: Citrus vinegar
Physical Description: Book
Creator: McNary, Robert R.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1960
Copyright Date: 1960
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Bibliographic ID: UF00027160
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
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Resource Identifier: aen7764 - LTUF
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Full Text





HISTORIC NOTE



The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida







Bulletin 622



UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATIONS
J. R. BECKENBACH, Director
GAINESVILLE, FLORIDA

(A contribution from the Citrus Experiment Station in cooperation
with the Florida Citrus Commission)













CITRUS VINEGAR



ROBERT R. MCNARY and MARSHALL H. DOUGHERTY
















Single copies free to Florida residents upon request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE. FLORIDA






















CONTENTS

Page
INTRODUCTION ....... .........................-..-. ..3....... 3

THE VINEGAR PROCESS .................. ....-- ...-.--.. -- -----------........--..... 3

The Orleans Process ............-- -----.... ..- .. .... .. ..................- 4

The Generator Process .............................. .. --- ---- ................ 4

The Submerged Fermentation Process .-----.............. --.. ............----. 5

EXPERIMENTAL PROCEDURE AND RESULTS ..........................-............. 6

The Alcoholic Fermentation ---........................... --. ---.- ......--..-- 6

The Acetic Acid Fermentation ..-................--..------ ...--..--.......--.. 6

The Acetic Acid Bacteria ..---...............-- -- --..-..-..- --- ...-..---.. .. 12

The Effect of Peel Oil .--..-... -----.....--------. ..-................ 13

Use of Pectic Enzymes ---.-..--..----.----..--........ .-...--....-- ..... 15

ECONOMIC ASPECTS .........----..............-.. ---... --------- -...-...... 17

FEDERAL REGULATIONS .-....------.... .............-------..........---------- 21

CONCLUSIONS ..- -...--... ..--- -------- -. ...--------.............- 21

ACKNOWLEDGMENTS -- .------. -............--------------....--...-- -..-...... ......... 22

LITERATURE CITED ----- --....- --...- --- -----...----------..................... .... 22















July 1960










CITRUS VINEGAR

ROBERT R. MCNARY and MARSHALL H. DOUGHERTY

INTRODUCTION
In this country, the traditional raw material for vinegar pro-
duction has been apple juice or cider. Cider vinegar is the
standard with which other vinegars are compared for flavor and
cost. Within the last decade or two, the commercial production
of wine vinegar has shown considerable growth. While the
volume is not yet large compared to cider vinegar, it is sold at
a considerably higher price, exclusively for table use. In view
of this, it was decided to examine the possibility that citrus
juices and by-product liquids could produce vinegars of com-
petitive quality and cost. The investigations described in this
bulletin were designed to answer these questions.
Prescott and Dunn (2) and bulletins of the United States
Department of Agriculture, both early (3) and recent (4), men-
tion oranges as one of the many possible raw materials for vine-
gar making. However, the authors have been unable to find
reference to commercial production. Difficulties with the de-
velopment of off-flavors and the obtaining of a clear, stable
product may have discouraged earlier workers. Also, the fact
that citrus juices, in general, have insufficient sugar to yield a
vinegar of at least 4 percent acetic acid (the minimum require-
ment) may have further contributed to a lack of interest. Since
the development of commercial, frozen orange concentrate,
orange juice of almost any concentration and amount can be
readily obtained. If desired, 100 grain (10 percent acetic acid),
or stronger, vinegar now can be made from concentrated orange
juice that has been adjusted to the proper concentration.

THE VINEGAR PROCESS
Vinegar making is a 2-step process. Sugars are first fer-
mented by yeasts to an alcoholic liquor, which is then converted
into vinegar by acetic acid bacteria. The yeast step is essen-
tially anaerobic in nature and decreased yields of alcohol result
from contact with air. On the other hand, air is necessary for

1 McNary, formerly Biochemist, and Dougherty, Assistant Chemical En-
gineer, Florida Citrus Commission and Citrus Experiment Station, Lake
Alfred, Florida.







4 Florida Agricultural Experiment Stations

the oxidation of the alcohol to acetic acid by the bacteria in the
second step. The 2 steps therefore must be carried out
separately in different equipment and, if desired, they may be
performed with extended intervals between them. As a matter
of fact, in making cider vinegar it is customary to crush the
apples and ferment the juice with yeast as rapidly as possible
during the 6 or 8 weeks that ripe apples are available, but to
store the fermented juice and make into vinegar during the
remainder of the year.
There are 3 main processes by which the alcoholic liquor can
be converted into vinegar. They are the slow or Orleans process,
the generator process and the submerged fermentation process.
All 3 have been used to produce citrus vinegar. They differ in
their speed of conversion which is directly related to the rate
at which oxygen from the air can be absorbed by the bacteria
and utilized.
The Orleans Process.-The slow or Orleans process utilizes a
shallow vessel containing the acetifying liquor. The vessel has
an opening at the top to admit air. This opening should be
screened to exclude insects. The vinegar bacteria grow in a film
on the surface of the liquor in contact with the air. Since the
acetification activity takes place in this film, the rate of acetifica-
tion is limited by the relative area of the film. In comparison
with the other processes, the rate of vinegar production by this
means is very slow. However, the quality of the product is ex-
cellent. The efficiency of conversion of alcohol to acetic acid is
somewhat less than the other processes. Since it requires little
attention, this procedure is favored when small amounts of
vinegar are being produced.
The Generator Process.-Faster conversion of the alcohol can
be obtained by increasing the contact among the alcoholic liquor,
acetic acid bacteria and oxygen from the air in a generator type
fermenter. In this fermenter, which has been in commercial use
for over 100 years, the liquor is trickled down through a tower
packed with beechwood shavings. The bacteria attach them-
selves to the shavings. Their acetification activity produces
heat, which causes a continuous updraft of air through the gen-
erator. By this means the necessary oxygen is supplied for
oxidizing the alcohol. The liquor reaching the bottom is re-
turned to the top for another passage over the shavings. This
is continued until practically all of the alcohol is converted to







Citrus Vinegar 5

acetic acid. The finished vinegar is drawn off and stored in the
absence of air. Otherwise the bacteria, in the presence of oxy-
gen, will destroy the acetic acid that they have just produced.
The Submerged Fermentation Process.-This process differs
from the other 2 in that the bacteria are uniformly distributed
throughout the liquid being acetified. Oxygen is supplied for
the oxidation by dispersing air in fine bubbles throughout the
liquid. Vigorous agitation accompanies, and is necessary to, the
dispersion.
The process was developed first in Europe but has been im-
proved to a high level in this country within the last 3 years (1).
The more intimate contact among oxygen, bacteria and the
acetifying liquid speeds up the acetification activity. Further-
more, the conversion of alcohol to acetic acid in the submerged
fermentation comes closer to theoretical values. Ninety-eight
percent conversion has been achieved in a properly operated
fermenter, which may be compared with 80 to 88 percent con-
version in a packed generator and 70 to 80 percent in the Orleans
process. The economic implications of the much improved effi-
ciency of the submerged fermentation are obvious.
The more rapid acetification by submerged fermentation de-
mands closer control of the 3 major factors that influence the
acetification activity, namely the rate of feeding the wine, the
rate of aeration and the temperature. Since the fermentation
generates its own heat, it is relatively simple to control the tem-
perature by regulating the amount of cooling water passed
through a coil in the fermenter. This is usually done auto-
matically.
The rate of feeding the wine, or mash as it is sometimes
called, must be adjusted closely to the activity of the bacteria
present. At present this is not subject to automation. The de-
cision of whether to increase or decrease the feed rate must be
made from the results of frequent determinations of the per-
centages of acid and alcohol in the fermenter liquid. The feed
rate must be adjusted closely to the activity of the bacteria, or
the optimum alcohol concentration will not be maintained.
In a similar manner, the rate of aeration must also be cor-
related with the activity of the bacteria. Too little air starves
the vinegar bacteria and too much air inhibits their activity.
The effect of changing the aeration rate on the acid production
is the basis for determining the optimum rate.







6 Florida Agricultural Experiment Stations

EXPERIMENTAL PROCEDURE AND RESULTS
The Alcoholic Fermentation.-Before vinegar can be made,
the raw material must first undergo an alcoholic fermentation
with yeast. The first few batches of citrus vinegar were made
from juice that was fermented with a strain of Hansen type
wine yeast. It has been established that the strain of yeast does
not appreciably affect the quality of the vinegar. Consequently,
with the exception of the few batches mentioned, all of the citrus
vinegar was made from wine fermented with Baker's yeast pur-
chased in dry form at a nearby grocery. With adequate inocu-
lation the yeast fermentation proceeds quickly and is about
complete in 3 days. In 4 to 6 days the yeast has settled and
the supernatant wine may be drawn off and filtered. This oper-
ation should not be delayed more than 2 or 3 days; otherwise
off-flavors may develop.
The Acetic Acid Fermentation.-The first vinegar produced in
this laboratory was made in a packed generator. The generator
consisted of a glass tube 2.75 inches in diameter and 23.5 inches
long filled with beechwood shavings. The alcoholic liquor was
pumped to the top of the generator by means of a Sigmamotor
pump, which was adjusted so that the feed rate was virtually
drop by drop (4.9 ml. per minute). The partly acetified liquor
emerging at the bottom was caught in a 500 ml. bottle and re-
turned to the top of the generator by the pump. When the acetic
acid concentration reached a maximum, some of the vinegar
was drawn off and a like amount of alcoholic liquor was added
in its place and the process was continued.
The air needed for the bacterial oxidation was obtained from
the compressed air supply in the building. This permitted
measurement of the air with a capillary flow meter and adjust-
ment of the flow rate to the amount (0.0005 cu. ft. per minute)
found to be best by experiment. The temperature of the gen-
erator was controlled by placing it inside a cabinet which was
electrically heated and regulated by a thermostat at 900F. The
original culture of acetic acid bacteria was obtained as an un-
pasteurized and unfiltered sample of vinegar from a commercial
vinegar manufacturer.
The important finding in the first attempt to make citrus
vinegar was the fact that vinegar was made at a satisfactory
rate and a satisfactory yield or conversion rate from alcohol
to acid was obtained. The generator was kept in continuous
operation for 29 months making vinegar from orange, grape-







Citrus Vinegar 7

fruit, tangerine and citrus molasses wines. Most of these prod-
ucts were of good or excellent quality.
Since the recent advent of the "submerged fermentation"
process for vinegar manufacture has rendered the generator
packed with shavings obsolete, it would seem superfluous to
describe in detail all of the experiments carried out with the
generator. It is sufficient to say that the generator produced
citrus vinegars worthy of further investigation.
Our generator had the disadvantage of having a very small
capacity and most of the product was used up in analyses.
Furthermore, only one batch could be acetified at one time. In
order to enlarge the quantity of citrus vinegar produced and to
investigate a large number of variables simultaneously, the slow
or Orleans process was used. Nearly 40 gallons of grapefruit
vinegar were made in 2 wide-mouth glass jars of 5-gallon ca-
pacity. The jars were filled about half full with a mixture of
the wine, or fermented juice, and vinegar which contained active
acetic acid bacteria. A film of the bacteria formed on the liquid
surface. When maximum acetic acid concentration was obtained,
about half the vinegar was drawn off and replaced with an equal
volume of wine. Care was taken not to disturb the surface
film unnecessarily. The vinegar made in this way was excellent
and created considerable interest among those receiving samples.
Indeed, the Orleans process has the reputation of producing the
highest quality vinegar. Its slowness permits the formation
of esters that enhance the flavor.
The Orleans process was also used to produce small batches
of vinegar from fruit that had been severely frozen during the
cold weather of December 1957 and January 1958. The vinegar
from this frozen fruit was as good as that from otherwise sound
fruit.
The use of the Orleans process for these investigations had
the advantage that the batches could be kept small so that less
material was required. Furthermore, a number of batches could
be in process at the same time. As usually carried out, 100 or
200 ml. of an active vinegar culture was added to 200 or 300
ml. of the wine that was desired to be acetified into vinegar and
the mixture was placed in a 3- or 4-quart wide-mouthed bottle
or jar. The open mouth was covered with 3 layers of cheese-
cloth to keep out insects. As acetic acid was produced, more
wine was added until the jar was 1/2 to 2/3 full. When the maxi-
mum acidity was reached, the vinegar was filtered, pasteurized







8 Florida Agricultural Experiment Stations

and bottled. Samples for acid determination were removed by
inserting a pipette through the surface film. Wine additions
were made with minimum disturbance of the film by running
the wine down the inside wall of the jar or through a funnel
with its stem inserted through the film.
While both the Orleans and the packed generator processes
have served very useful purposes in the development of quality
vinegars from citrus fruit, the only process that needs to be
considered for commercial production at present is submerged
fermentation. The increased efficiency of the latter process has
made the others obsolete.

A






F






s K






I M





Fig. 1.-Cutaway drawing of the Cavitator. A, variable speed drive;
B, clear plastic tank; C, cooling water inlet; D, cooling water outlet; E, feed
inlet; F, stainless steel lid; G, draft tube; H, product outlet; J, thermometer;
K, plastic baffle; L, cooling coil; M, rotor mounted on hollow shaft.







Citrus Vinegar 9

The fermenter used in the submerged fermentation experi-
ments was a pilot plant model "Cavitator"* consisting of a 20-
gallon transparent plastic tank with vertical baffles to stop vortex
action of the liquid. A helical coil of stainless steel tubing inside
the tank carried cooling water for temperature control. The
rotor with its hollow shaft and the draft tube were made entirely
of stainless steel and were attached to the stainless steel lid.
Rotation of the rotor sucked air down the hollow shaft and
dispersed it in fine bubbles in the liquid. Practically instan-
taneous mixing of the liquid was also produced by the rotor
action. Power for driving the rotor was supplied by a 1/4 hp.
U. S. Varidrive motor.
Figure 1 shows a sectional view of the Cavitator. A Sigma-
motor pump with attached speed changer and motor was used
to meter the wine feed from the supply tank to the Cavitator.
With this equipment it was possible to vary the feed rate from
2 to 20 gallons per day as needed. Tygon tubing was used to
transport both wine and vinegar between different pieces of

Registered trademark of Yeomans Brothers Company, manufacturer.

Fig. 2.-Pilot plant for making citrus vinegar. A, feed tank; B, Sig-
mamotor feed pump; C, variable speed drive; D, cavitator; E, temperature
controller and recorder; F, solenoid valve in cooling water line; G, foam
trap; H, product tank.


A H





















.........







10 Florida Agricultural Experiment Stations

equipment. Feed and product tanks consisted of open-end 55-
gallon steel drums with plastic liners made of polyvinyl chloride.
Cheesecloth was draped over the open ends to keep out insects
and plywood covers prevented appreciable evaporation. Figure
2 is a photograph of the vinegar making assembly.
The first submerged fermentation run was made at a tem-
perature of 900F., but during subsequent runs 86'F. was main-
tained. At the higher temperature the bacteria were more
active and converted alcohol to acetic acid more rapidly, but
they were also much more sensitive to the concentration of alco-
hol in the acetifying liquid. When the alcohol concentration
exceeded about 0.080 percent by weight, conversion to acetic
acid was suppressed. When the concentration was below 0.030
percent, the bacteria started to oxidize some of the acetic acid
to carbon dioxide and water. Maintenance of the alcohol con-
centration between these 2 points was a difficult task and de-
manded constant supervision and frequent alcohol determina-
tions. At 860F. alcohol concentrations of 0.200 to 0.300 percent
were tolerated.
Experience has shown that 0.100 percent of alcohol probably
was close to the optimum concentration under the conditions
usually encountered in continuous operation. Concentrations of
alcohol in excess of the optimum can lead to loss of this material
by volatilization in the air stream as well as retarding the
bacterial activity.
Approximately 550 gallons of various citrus vinegars were
produced by submerged fermentation. The varieties were
orange, grapefruit and tangerine juice vinegars and orange peel
vinegar. Ordinarily this quantity of vinegar could have been
produced in about 40 days of continuous operation with the
equipment used. However, to reduce mixing of the different
varieties to a minimum, the Cavitator was drained to 5 gallons
before starting production of a new variety of vinegar. In this
way, mixing of the old variety in the new was held to 5 percent
or less.
Starting each time with the Cavitator less than 14 full re-
quired slow rebuilding of the culture and extended the total
length of operations to nearly 150 days. If a sufficient amount
of the new variety had been available from previous operations
to fill the Cavitator at the beginning of the run, an appreciable
amount of the starting-up time could have been saved. Acetifica-
tion efficiency also suffered from this variation in production







Citrus Vinegar 11

rate. Acetification efficiencies of 95 percent or more were en-
countered only toward the end of each run.
With continuous operation over an extended period there is
every reason to believe that production rates and efficiencies in
the case of citrus vinegars would be just as high as obtained
by Cohee and Steffen (1) with cider and other vinegars.
Two different quantities of orange juice vinegar were pro-
duced by submerged fermentation. In one, the sugar content
of the juice was augmented by the addition of corn sugar before
yeast fermentation so that a 60 grain vinegar could be made.
Since this material was not heated until final flash pasteuriza-
tion, the vinegar produced was light yellow. However, on stor-
age, it darkened to a typical amber or brown color. The other
quantity of orange juice vinegar was produced from juice that
was concentrated to 160 Brix before yeast fermentation. It
was noticed that the latter had more characteristic flavor than
the former orange juice vinegar. The quality of both was ex-
cellent. Excellent vinegar was made also from tangerine juice.
Grapefruit juice vinegar was interesting, not only because
of its excellent flavor but also because of the high citric acid
content of the original juice, which enhanced the total acidity
of the vinegar by almost 40 percent. Indeed, the total acid
strength of this vinegar could not be adjusted to below 56 grains
without the acetic acid content being reduced to less than 4 per-
cent. Since sourness is the principal characteristic of vinegar,
the additional citric acid sourness of grapefruit vinegar may be
used to advantage.
Particular mention should be made of the vinegar produced
from "press liquor" which is the liquid obtained when citrus
peel is ground, treated with lime and pressed. The press cake is
dried and sold for cattle feed. The press liquor may be partially
evaporated and added to the press cake for further drying or
it may be concentrated to citrus molasses and sold as such. Since
it contains 6 or 7 percent fermentable sugar, press liquor is a
possible raw material for vinegar. It is also practically a waste
material and therefore cheap.
The vinegar made from press liquor was darker in color than
the other vinegars and had an entirely different aroma and flavor.
The aroma was more "fruity" than the other varieties. Whether
these differences will be for better or worse remains to be seen.
The name "orange peel vinegar" has been tentatively used
here, since it was believed "press liquor vinegar" was not prop-







12 Florida Agricultural Experiment Stations

early descriptive and might be misinterpreted. In the present
case only orange peel was used in the production of the press
liquor. Had a mixture of orange and grapefruit peel been used,
the product would have been called "citrus peel vinegar."
The lime treatment of the ground peel during the production
of press liquor neutralizes practically all of the free organic
acids present. Consequently, the sourness of citrus peel vinegar
is derived almost entirely from the acetic acid present.

TABLE 1.-TYPICAL FREE ACID CONTENT OF CITRUS VINEGARS.

Type Vinegar Percent Percent Percent
STotal Acids Citric Acid Acetic Acid
Orange vinegar .......... 5.07 0.87 4.20
Grapefruit vinegar .... 5.60 1.52 4.08
Tangerine vinegar ...... 5.00 0.62 4.38
Orange peel vinegar .. 5.00 0.00 5.00


At times foaming has been a problem in making vinegar by
submerged fermentation (1), but it can be controlled by anti-
foam agents. Citrus vinegars were no exception but their foam-
ing tendencies were not excessive. Citrus peel vinegar from
press liquor did foam somewhat more than that made from
juices. It was noticed that foaming was more pronounced when
the feed rate to the fermenter was equal to or somewhat in
excess of the capacity of the culture to convert the alcohol into
acetic acid. Maximum production from a fermenter doubtless
would require the use of some antifoam at all times. When
maintained in a slightly "starved" condition, the submerged fer-
mentation can be operated without using antifoam.
The Acetic Acid Bacteria.-As stated previously, the original
culture came from a commercial source. This sample was used
to inoculate the packed generator. All of the Orleans process
batches were inoculated from vinegar made in the generator and
the Cavitator was inoculated with bacteria from Orleans process
vinegar. Since vinegar is a low cost and competitive product,
the expense of maintaining and using pure cultures cannot be
justified in commercial practice.
Fortunately, few organisms can survive the conditions in vine-
gar generators and those that do seldom cause trouble. Adher-
ing to commercial practice, no attempt was made to exclude air-







Citrus Vinegar 13

borne microorganisms in making citrus vinegars. There is reason
to doubt, therefore, that all batches were produced by the same
strain of bacteria. Microscopic examination of the culture at
different times did show differences in morphology, especially
during the submerged fermentation experiments. At one time,
when the temperature of the Cavitator reached 920F. for sev-
eral hours, due to malfunction of the controller, the bacteria
were all small diameter diplococci. Ordinarily they were short,
rod-shaped bacilli but not always uniform in diameter. The
different appearance of the bacteria at different times may have
been pleomorphic phases of the same strain or the predominance
of different strains under varying conditions. It apparently is
not important to know the answers to these questions in practical
vinegar making.
Effect of Peel Oil.-All citrus juices contain a small amount
of an essential oil which in trade parlance is generally referred
to as "peel oil" because nearly all of it is found in the peel of
the fruit. This oil is responsible for a considerable portion of
the characteristic flavor and aroma of citrus juices. It is also
responsible for some of the off-flavors that may develop when
citrus juices are mishandled.
The initial feed for the generator consisted of a batch of
orange wine. The wine was obtained from orange juice which
was brought to 16 Brix by the addition of sugar before ferment-
ing with a wine-type yeast. After fermenting, the wine was
stored at room temperature for several months. During storage,
it darkened and developed a "terpeney" or "furniture polish"
odor and taste. It was not known, at first, whether this flavor
would carry over into the finished vinegar. This wine would
not have been used except for the fact that it was the only
fermented citrus juice on hand at the time that the culture of
vinegar bacteria arrived and it was feared that the activity of
the culture might be lost if it were not put to work immediately.
The packed generator was started, using this batch of off-
flavored wine. It was found that the off-flavor persisted and a
vinegar was produced that probably would have limited accept-
ability. The peel oil in the original juice was suspected as the
source of off-flavor and subsequent experience has proved this
to be so.
It had been found (5) that complete removal of peel oil from
citrus juices could be achieved by adding an equal volume of
ethyl alcohol to the juice and then distilling off the alcohol. The







14 Florida Agricultural Experiment Stations

peel oil was carried over into the distillate. A few liters of orange
juice were treated in this manner to remove the oil and then
fermented with yeast and finally made into vinegar by the slow
process. Even after months of storage there was no evidence of
the development of off-flavor. This treatment, while effective, nat-
urally was too cumbersome for a practical de-oiling procedure.
It has been known for a long time that peel oil is attached to
or intimately associated with the pulp or suspended particles in
citrus juice. Any procedure that reduces the amount of pulp
in the juice will reduce the amount of oil. A "soft squeeze"
during the extraction of the juice from the fruit and passing the
juice through a finisher with a fine screen are helpful. Also,
partial evaporation of the juice either with or without vacuum
will reduce the oil content. None of these operations, however,
will entirely remove the oil.
Peel oil and its effect can be eliminated by passing the juice
through a finisher with a fine screen (0.02" holes or less), fol-
lowed by evaporation to about 2/3 of its volume and then ferment-
ing with Bakers' yeast using a substantial volume (5 to 10
percent) of starter. As soon as the fermentation activity slows
down and the yeast settles (3 to 5 days), the supernatant liquor
is decanted and filtered so that only haziness remains. If filtra-
tion is delayed, the blanket of carbon dioxide above the liquid
surface becomes dispersed, allowing oxygen from the air to reach
the remaining peel oil. Oxidation of the peel oil produces the
"terpeney" flavor which cannot be removed effectively.
The amount of peel oil present in press liquor should receive
special mention. As obtained from the presses, this liquor con-
tains relatively large amounts of oil, sometimes exceeding 1
percent by volume. The most practical method of rendering the
liquor suitable as a raw material for vinegar was found to be
heating it to 1800 to 2000F., allowing it to stand several hours
and drawing off the portion that is fairly free of suspended
solids. About 60 to 70 percent of the original volume thus ob-
tained can be filtered clear without much difficulty. The re-
mainder may be returned to the molasses operation.
The filtered liquor can be evaporated at atmospheric pressure
or under vacuum to the desired concentration before fermenta-
tion and acetification. After acetification, the vinegar should
be pasteurized before final filtration since heating the vinegar
usually causes some additional material to precipitate, resulting
in a cloudy or hazy product.







Citrus Vinegar 15

Use of Pectic Enzymes.-Another problem encountered in
the production of citrus vinegar was that of obtaining a clear
product. Turbidity and cloudiness are expected and protected
in citrus juices but must be eliminated in vinegar made from
them. The pectic substances present make filtration painfully
slow.
The juice normally contains an enzyme, pectinesterase, which
removes the methoxyl groups from the pectin molecule. This
action, however, is not enough to make the juice readily filter-
able. There are available a number of commercial enzyme prep-
arations derived from certain molds that will hydrolyze pectin all
the way to galacturonic acid. Citrus juices treated with these
enzymes can be filtered with reasonable amounts of filter-aid to
produce a clear liquid that contains no peel oil and therefore can
be used to produce a vinegar that is free of off-flavors.
The rate of reaction of these enzymes is relatively slow and
it has been found advantageous to allow them to act at the
same time that yeast is fermenting the sugars of the juice to
alcohol. Since the yeast fermentation requires from 3 to 5 days,
this extended period permits the use of minimum amounts (about
0.01 percent by weight) of pectic enzymes to destroy the slimi-
ness of the juice. This is a great advantage. Furthermore,
pectic enzymes are relatively expensive and the quantities should
be held to a minimum in any event.

TABLE 2.-METHANOL CONTENT OF CITRUS VINEGARS.

Type Vinegar Percent Methanol
by Weight
Tangerine vinegar .-..............--.... ....-- .... ..... 0.010
Orange vinegar --..... ---......... ---- ... ............. 0.010
Grapefruit vinegar ---..----............-- ...----......-- .... 0.0094
Grapefruit vinegar ...................... ... ............. -0.0096
Citrus molasses vinegar .......................-............ 0.0078


A side effect of the use of pectic enzymes was found to be the
release of methanol in the juice due to the splitting-off of me-
thoxyl groups. While methanol is a poison when ingested in
appreciable amounts, the quantity found in citrus vinegar was
not believed to be of any significance. Nevertheless, it was







16 Florida Agricultural Experiment Stations

thought that the quantities found should be recorded to forestall
exaggerated inferences in the future. Table 2 gives the results
of analyses of several different batches of citrus vinegar. Ap-
parently the methanol content of citrus vinegars runs in the
neighborhood of 0.01 percent. As far as known, there is no
established limiting concentration of methanol in vinegar.
The first few times pectic enzymes were used care was not
taken to add only the minimum amount required to hydrolyze
the pectin. After the vinegar was finished and stored for several
weeks, a brown sediment appeared in the bottles. The sediment
was soluble in dilute sodium hydroxide solutions and was re-
precipitated upon acidification. It gave negative tests for carbo-
hydrate. It contained 4.87 percent nitrogen, indicating that it
might be a protein. Hydrolysis to amino acids was found to
be difficult, but was finally accomplished by heating the sediment
in a sealed tube at 150'C. with 20 percent hydrochloric acid.
Analysis of the hydrolyzate by paper chromatography revealed
the presence of 11 amino acids. By this time the pectic enzyme
preparation was suspected as the source of the sediment. When
a sample of the enzyme was treated in the same manner, the
pattern of amino acids on the paper chromatogram was so
strikingly similar that there was no doubt that the sediment was
derived from the enzyme added. A molecular weight determi-
nation of the sediment gave a value of 3,000,000 to 5,000,000,
whereas unused enzyme gave 90,000.
Apparently in the finished vinegar, the spent enzyme grad-
ually polymerizes to a large molecule that is no longer soluble
and therefore precipitates as sediment. The slowness of pre-
cipitation may be judged by the fact that 4-year-old vinegar
showing sediment was filtered clear and stored in a clean bottle.
In a few weeks additional sediment formed. The presence of
the sediment is objectionable only because of its unsightliness
which would reduce the salability of the product.
Because of this undesirable effect of the pectic enzyme prep-
aration that was used, a survey was made of available commer-
cial pectinases to determine if there were any that did not cause
sediment formation. Small quantities of vinegar were made by
the Orleans process using each of the different commercial sam-
ples. Considerable variation was found among the 14 different
preparations, both in their ability to hydrolyze pectin in the
juice and in their sediment-forming tendency. All enzymes but
1 produced some sediment in vinegar after 6 months storage







Citrus Vinegar 17

when used at concentration of 0.25 percent or more. There were
a few that had adequate pectinase activity at concentrations of
0.015 to 0.020 percent by weight, yet did not give rise to sedi-
ment formation at this level after 6 months storage.
An additional benefit from the use of pectic enzymes may be
found in their ability to hydrolyze the flavonoid glucosides that
occur in citrus products. For example, the glucoside naringin
is found in grapefruit and is responsible for the characteristic
bitterness of this fruit. Similarly, hesperidin is found in oranges
but is flavorless or nearly so. Ordinarily the bitterness of na-
ringin in grapefruit vinegar is suppressed by the sourness of
vinegar and is not noticeable at usual concentrations. Never-
theless, 1 batch of grapefruit vinegar was prepared from
ground whole fruit with the result that the naringin content
exceeded saturation concentration in the product. Some of the
glucoside precipitated out on storage. Also, a batch of orange
vinegar was made that developed a precipitate of hesperidin on
storage. In cases such as these, hydrolysis of a portion of the
glucoside by enzyme action would protect the appearance of the
product.
The different enzyme preparations that have been tried had
widely varying glucosidase activities. Selection of the most
suitable preparation would therefore be important.

ECONOMIC ASPECTS
The quality of vinegar made from orange, grapefruit and
tangerine juices appears to be exceptionally good. Most people
who have been given samples have returned for more. A num-
ber of food editors of national publications have praised them
highly. Samples sent to one of the largest chains of super-
markets in the country were evaluated by their taste panel and
judged superior to cider vinegar and were said to have an inter-
esting and distinctive flavor.
In spite of these favorable expressions, the place that citrus
vinegar might achieve in commercial channels can be determined
only by further market research. Should public acceptance be
favorable in comparison with wine vinegars, it would be possible
to manufacture citrus vinegar at a fairly good profit but with a
somewhat restricted market. Should it be possible to produce
citrus vinegars as cheaply as cider vinegar, a truly large market
would become available. Without a background of full-scale oper-







18 Florida Agricultural Experiment Stations

ating experience, there is a reasonable doubt that citrus vinegars
could compete on an equal cost basis with cider vinegar.
Citrus peel vinegar should be considered separately, since its
flavor is entirely different from that made from juices. Also,
samples of this material have not had wide distribution and
opinions on its quality are not yet available.
While it is possible for one to become enthusiastic about
citrus vinegars from a quality standpoint, a consideration of
costs of production may have a temporizing effect. In the dis-
cussion here, a different basis has been used for determining
the cost of the raw material for making orange, grapefruit, tan-
gerine and citrus peel vinegar. The disadvantage of this pres-
entation is realized. Nevertheless, the derivation of these figures
is based on current practices of the citrus industry.
For example, most oranges are now purchased on the basis
of a given price for each pound of solids in the juice. This has
become customary since the great expansion in the production
of frozen orange concentrate. Grapefruit and tangerines, still
largely fresh fruit items, are purchased on the basis of a field
box. Variations in juice yield and sugar content do not affect
the price proportionately. Citrus peel juice, known in the in-
dustry as "press liquor", can be purchased on a gallon basis
which is not directly dependent upon the original fruit cost.
Recently orange juice suitable for frozen orange concentrate
production sold for 65 cents per pound of juice solids based on the
Brix determination. In other words, a juice having a Brix reading
of 110 would be considered as containing 11 percent juice solids.
About 70 percent of orange juice solids are fermentable sugars,
hence 65 cents would buy 0.7 pound of these sugars. When fer-
mented with yeast, the sugars yield just about 50 percent by
weight of alcohol. The 65 cents would therefore buy 0.35 pound
of alcohol which, when acetified, would make 0.46 pound of acetic
acid. This, in turn, would produce 11.5 pounds of 40 grain vine-
gar. The 11.5 pounds of vinegar would be equivalent to 1.35
gallons. The raw material cost for 40 grain orange vinegar would
then be 65/1.35 or 48 cents per gallon. This would be entirely
too high-priced except possibly for the small volume that might
be sold at high prices to the gourmet trade.
These figures are admittedly on the extreme side; 65 cents
per pound of juice solids is a very high price and is not expected
to remain at this level. Nevertheless, more normal prices of
40 to 45 cents per pound of orange juice solids are believed







Citrus Vinegar 19

sufficiently high to eliminate orange juice as a source of vinegar
on a large scale. On the other hand, there are always available
moderate amounts of fruit and juice that, for one reason or
another, cannot demand maximum price. Much of this might
well be channeled to vinegar production.
In the case of tangerines, a large portion of the crop is seldom
harvested because of small size or maturity after peak demand
has passed. Doubtless, a considerable quantity of tangerines
could be obtained for little more than harvesting costs. Excel-
lent vinegar has been made at the Citrus Experiment Station
from somewhat over-mature tangerines. From 75 field boxes
of tangerines, 1261/2 gallons of 50 grain vinegar were made.
The yield of 1.68 gallons per box was less than expectation. It
was due to the low yield of juice as the result of using improper
extraction equipment. Normally the yield of vinegar could be
twice as much. Assuming a price of 30 cents per box of tan-
gerines and a yield of 2.52 gallons of 50 grain vinegar per box,
or 50 percent more than above, the raw juice cost of the vinegar
would be 13.5 cents per gallon. This compares favorably with a
raw material cost of 10.9 cents per gallon for vinegar made from
corn sugar. The latter is a white vinegar of lower quality than
citrus vinegar.
Grapefruit, because of its naturally higher acidity and nor-
mally lower cost than oranges and tangerines, deserves individ-
ual consideration as a source of vinegar. The citric acid content
of the juice is normally 0.9 to 1.5 percent. When partially con-
centrated so that the final product will have at least 4.0 percent
acetic acid, the citric acid content may be 1.5 percent and some-
times more. A 60-grain vinegar then can be made that has only
45 grains of acetic acid. Since sourness is the major character-
istic of vinegar, the citric acid in citrus fruit may be used to
advantage, especially in the highly acidic grapefruit. It is esti-
mated that adequate supplies of low grade grapefruit can be
obtained for 50 cents or less per field box. From this, it should
be possible to make about 3.5 gallons of 60 grain vinegar. The
raw material cost on this basis would be 14.3 cents per gallon.
Also deserving individual consideration is citrus peel vinegar
made from press liquor. Free citric acid here is negligible be-
cause of lime treatment during manufacture. On the other hand,
its low price of approximately 1.5 cents per gallon and its fer-
mentable sugar content of about 6 percent should make possible
the production of a low cost vinegar. Even though one third of







20 Florida Agricultural Experiment Stations

the liquor is discarded with the majority of the suspended solids
as explained earlier, the cost per pound of fermentable sugar
would be approximately 4.5 cents, which is less than the price
of corn sugar. Should the vinegar operation be charged with
only the proportion of liquor actually used, the cost per pound
of fermentable sugar is only 3.4 cents per gallon. Based on
these raw material costs, citrus peel vinegar should be competi-
tive with all other vinegars except possibly "distilled" vinegar.
It should be mentioned, however, that improved sanitary condi-
tions should prevail in the production of press liquor to be made
into products intended for human consumption. This may in-
crease its cost somewhat.
It is probable that processing costs of citrus vinegars may
be somewhat higher than other vinegars because of the extra
filtration required to avoid the effects of peel oil. Filter-aid re-
quirement for this filtration is estimated at not over 1.0 cent
per gallon and enzyme requirement at 0.6 cents per gallon. Power
and labor costs may bring the extra filtration cost up to 2.0 cents
or possibly 2.5 cents per gallon, depending upon the volume of
production. These figures may be excessive, since reliable sources
have stated that vinegar can be made on a large scale for 2.0
to 4.5 cents per gallon, not counting the raw material.
Vinegar making is traditionally a competitive business based
on large volume and low profit margins. Production of wine
vinegar is a possible exception, since it is relatively new and the
volume is not large. Orange vinegar has the least chance of
successfully competing on a price basis with established products,
unless the juice can be obtained at distress prices. Grapefruit
and tangerine vinegars have interesting possibilities, since it is
likely their juices can be obtained at low cost at certain times
of the year. Citrus peel vinegar has great possibilities as far as
costs are concerned, but remains to be tested for public accept-
ance.
Ordinarily citrus juices do not contain sufficient fermentable
sugar to yield 4 percent acetic acid in the finished vinegar with-
out partial concentration or the addition of some sugar. The
addition of sugar to citrus juices intended for canning is per-
mitted within limits as long as this fact is mentioned on the
label. It is not known whether the addition of sugar to juice
intended for vinegar making would be legal. Perhaps it would
be allowed if no additional water were added to adjust the grain
strength. Using sugar in this manner would reduce costs in







Citrus Vinegar 21

porportion to the amount added, since cane sugar is cheaper per
pound than the sugars in citrus juices. In the case of citrus
peel vinegar, however, the added sugar would be more costly
per pound than the sugar in the press liquor. Adding sugar here
would therefore be wasteful.
A batch of orange vinegar was made by submerged fermenta-
tion from juice that was fortified with sugar before fermentation.
The product was completely satisfactory, but on direct compari-
son with orange vinegar made from partly concentrated juice,
there was a noticeable dilution of flavor. Carried to extreme,
the addition of a large amount of sugar followed by water after
acetification could lead to a vinegar with no more flavor than
white vinegar.

FEDERAL REGULATIONS
Since vinegar can be made only from an alcoholic liquor,
Federal regulations must be followed. In reply to an inquiry,
the Internal Revenue Service stated "-vinegar produced by
acetification of wine would first require the manufacturer to
qualify a bonded wine cellar and thereafter to remove the wine
free of tax for use in the manufacture of vinegar." Part 240
of Title 26 (1954), Code of Federal Regulations, entitled "Wine",
covers the qualification of bonded wine cellars. In particular,
Sections 240, .120, .130, .225 and .650 through .662 are concerned
with the qualification of a bonded wine cellar and subsequent
removal of wine for the production of vinegar. Part 195 of title
26 (1954), Code of Federal Regulations, entitled "Production of
Vinegar by the Vaporizing Process," should also be consulted.
In order to avoid violations it would be wise for anyone planning
to enter into the manufacture of citrus vinegar to become familiar
with these and all other applicable regulations before proceeding
with construction or allotment of manufacturing space.

CONCLUSIONS
It is the opinion of many that the quality of citrus juice
vinegars is such that they should have a place in the vinegar
industry. Just where that niche may be can only be determined
by marketing trials. It is believed they compare favorably with
wine vinegars now being marketed, but only the public can con-
firm this. Until cost figures from commercial operations are
available, conservative estimates indicate that citrus juice vine-
gars cannot be manufactured as cheaply as cider vinegar. On







22 Florida Agricultural Experiment Stations

the other hand, citrus peel vinegar should be a low cost item.
Whether its flavor would be acceptable as a table vinegar or
whether it would be useful in prepared foods, sauces, dressings,
etc., remains to be seen.
The special characteristics of citrus juices and liquids due
to the presence of peel oil and pectin can lead to difficulties.
Unless eliminated early in the vinegar process, peel oil will be-
come altered and give rise to undesirable off-flavors in the final
product. Pectin interferes with the production of a clear product.
It can be eliminated by the use of hydrolyzing enzymes. How-
ever, undesirable sediment may form in the vinegar from the
spent enzyme. Also, traces of methanol have been detected in
vinegar made with the help of pectic enzymes. The methanol
was derived from the methoxyl groups of the pectin molecule.
It is believed that the necessary and sufficient conditions of oper-
ation have been described in this bulletin.

ACKNOWLEDGMENTS
The authors wish to acknowledge the assistance of the following persons.
Dr. R. F. Cohee, Food Technologist, Wheaton, Illinois, for his encourage-
ment and technological help, especially during the early portion of the
project. Mr. Grover Steffen, President, M. Steffen Company, Chicago,
Illinois, for supplying the original culture and beechwood shavings used
in the packed generator and for many courtesies during a visit to the
Chicago plant. Mr. D. W. Burgoon, President, Yeomans Brothers Company,
Melrose Park, Illinois, for the loan of a pilot plant model Cavitator for the
submerged fermentation studies. Mr. William Lawson, Feed Mill Foreman,
Adams Packing Association, Inc., for assistance in obtaining press liquor
of the desired type. Jacques Wolf & Co., Rohm & Haas Co., Takamine
Laboratories, and Wallerstein Laboratories for supplying samples of pectic
enzyme preparations. Many employees of the Citrus Experiment Station
for extracting and concentrating the fruit juices when needed.

LITERATURE CITED
1. COHEE, R. F., and GROVER STEFFEN. Makes vinegar continuously. Food
Engineering, 31, 3, 58-9. 1959.
2. PRESCOTT, S. C., and C. G. DUNN. Industrial Microbiology. P. 373.
N. Y., McGraw-Hill. 1949.
3. United States Department of Agriculture, Washington, D. C. Making
Vinegar in the Home and on the Farm. Farmers Bulletin No. 1424.
1924.
4. United States Department of Agriculture, Washington, D. C. Chemistry
and Technology of Citrus, Citrus Products, and By-Products. Agri-
culture Handbook 98. Nov. 1956.








Citrus Vinegar 23

5. WOLFORD, R. W., V. D. PATTON, and R. R. MCNARY. A method for
removal of peel oil from citrus juices and process liquids. Food
Technology, 6: 418-21. 1952.





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