L A Staff-IndustryCollaborative R e p o r t . WILL H. SHEARON, JR. Associate Editor
In collaboration with
L.
ESS than two decades ago the operations of the citrus fruit industry consisted mainly in shipping fresh and maned fruit and very limited quantities of citrus juice. An attempt to can apple cider in the early 1920’s met with failure; not until 1929 did w e d fruit juices become a commercial venture and the first citrus juicing plauts were just beginning to function well in the early 1930’s. Early juicing operations in Florida did not exceed three-quarters of a million cases until 1933; Texas was up to one-half million by 1935, and California and Arizona to onequarter million by 1936 (I). It was in the seaeon of 193536 that the juice plant of the Rio Crande Valley C i t m Exchange was put into operation, and this discussion centers mainly around that plant and the operations which have developed from it. Many articles have been written about various aspects of the citrusindustry. LueckandPilcher (M), indiscussing the technical aspects of canning fruitjuices, included an excellent bibliography. Heid (10,II) is the author of several articles, the two mentioned concerning utilization of citrus waste and vacnnm concentration of citrus juices; INDUS%U.&L AND ENQINEERIKC CHEXISTBY in 1934 carried a symposium on citrus fruits (24, $6, $6, 46). Van Antwerpen (43) discussed methods employed in Florida for the utilization of citras wastes in a plant operated independently of juicing and packing operations. Other articles have been descrip tive of general methods rather than specific operations.
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370
E. M. BURDICK, Director of Research, Tezsun Citrus Ezehange, Weslam, Texas
Bccauss the by-products of the citrus industry have assumed such g n a t importance, particularly with the advent of citrus molasses as a profitable commercial venture, it has seemed wise to try to tie all the operations into one related structure, and examine their dependence on each other. The Rio Grande Valley has assumed more and more importance in recent years as far as citrus growing and processing are concerned, as amply illustrated by Table I. During the war yeara and after, the planting of groves was particularly heavy; a total of 2,824,911 citrus trees of all kinds, or about 40,oOO acres, was put in during the %year period 194447 (41). I n the Valley, at Weslaco, ia the Texsun Citrus Exchange. Texsun, handling 40% of the Valley’s citrus crop, a successful cooperative that has the additional advantage of orning a plant which proceases citm from start to finish, produces almost 20% of the world’s supply of grapefruit juice, has modern equipment for juicing, peel dehydration, and citrus molasses production, and is currently doing advanced research on every problem connected with its operations, from gmding and wrapping of the fruit through juice mncentrstes. In the valley there is an annual average rainfall of only 25 i n c h e s a n c third of what is necessary for a successful citrus crop. Therefore the very existence of the Valley iS based on irrigation. The existence of the grower in this asea doRa not depend on the cooperative, but his problem of marketing,
.
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
TABLE I. TEXAS CITRUSPRODUCTION, THOUSANDS OF BOXES (40) Season Av. 1936-45 1944-45 1945-46 1946-47
Oranges 2942 4800 5000 5600
Grapefruit 16,121 24,000 23,300 25,000
TABLE 11. TEXSUN CITRUS EXCHANGE PRODUCTION Season 1941-42 1942-43 1943-44 1944-45 1945-46 1946-47 Present capacity
Juice, Cases 845,193 1,093,236 1,504,938 1,928,814 2,551,514 3,466,663 4,850,000
Feed, Tons 5 639 8:479 8,546 9,812 12,500 11,680 23,000
311
previous season. (Although various sizes of cans are filled, all reports go out on the basis of No. 2 cans, which hold 18 ounces.) This increase was brought about by the installation of latemodel, efficient juice extractors and more efficient can-filling machines. Since Texsun produces only single-strength juices and seotions (although research is being done on concentrates), operations can be divided into five spheres: packing, juicing, sectioning, dehydrating, and citrus molasses production.
Molasses, Gallons
.....
..... ..... .....
125,000 352,000 760,000
greater returns from his crop, and a stable price structure are certainly eased by its existence. Texsun has a membership of over 3000, and has its own veneer plant at Roseland, La., and box factory at Weslaco, besides various packing plants and the plant a t Weslaco. Started in 1932 as the Rio Grande Valley Citrus Exchange, the name was changed to Texsun Citrus Exchange in 1946, and it is the third largest citrus fruit cooperative in the United States. I n contrast to California cooperatives, which market mostly oranges, Texsun markets mostly grapefruit; only about 17% of the crop handled is oranges. In addition to grapefruit and oranges, some lemons may be processed, depending on market conditions. I n general, however, Texsun has not found the processing of lemons to be favorable economically, because of the small quantity involved and the inherently poor keeping qualities of the juice. Besides the juices, and a grapefruit-orange juice blend, special pink-meated juice is canned, along with fruit sections. The Rio Grande Valley is the only section of the country where it has ever been possible to grow the red variety of grapefruit. In the 194647 season Texsun handled 122,275 tons of juice% fruit; its growth during the last few years is shown in Table 11. The average recovery of juice in the 1946-47 season was 27.14 cases per ton, an increase of almost four cases per ton over the
PACKING PLANT
Packing operations are scattered, and each of the fourteen associations under the cooperative has its own packing plant. Citrus fruit is picked by size. In almost all Texas pickings, except where fruit of all sizes is stripped from the tree, the method commonly used is “ring picking.” The tool consists of a metal ring with a small thumb ring attached; by applying the ring to the fruit the foremen of the picking crews determine whether to pick. Rings of different sizes are available, and a 4-inch ring will just pass a size 80 grapefruit. Generally speaking, sizes 80 or larger are picked during “ring picking.” Expert pickers sometimes use visual methods entirely, but whether by actual or visual methods, these determinations relate only to size. The question of maturity is a very important one and is determined by a representative of the State Department of Agriculture. Citrus fruit never actually “ripens”; it matures, and the best measure of maturity found so far is the total solids content and the ratio of solids to acid measured in conjunction with the volume of the juice. The original state maturity law (88) required a minimum total solids content of 10% and a sugar-toacid ratio of 7 to 1. During the 1931-32 season the Texas Legisl a p r e passed H.B. 500, entitled the ‘‘New Citrus Fruit Law” (May 28, 1931), in which the Commissioner of Agriculture was given the power to prescribe additional seasonal requirements, including juice volume, one of the outstanding improvements to the maturity law. The mature fruit, however, is graded according to federal specifications. Taylor and Coman (37, 8) discuss the quality of citrus from the legal and health standcoints. The picked fruit is brought in field boxes to the packing plant and placed in the “sweat room,” where with the aid of heat, mois-
f
Canning the Juice
INDUSTRIAL AND ENGINEERING CHEMISTRY
372
IL
Vol. 40 No. 3
DRAWN OFFASTOP LAYER
RAW JUICE JUG€ T I N 8 5
SchematicFlow Diagram of Deoiling and Deaeration Unit
CIRCULATING PUMP.
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J C U I U U UWC
r PROCESS SERIE!
JUICE
ture, and 2 to 3 p.p.m. of ethylene, the chlorophyll which masks the color is bleached out. This operation occurs durine; only the early part of the season,and at the end of the seaaon it LB usual1 necessary to use thia eame room for “sterilising” the fruit steam. bot air. etc.. because of the Mexican fruit flv. “ . The fruit, is then washed wit6 water as cold as is m i b l e to be comnatible with satisfnctory zng and waxin , add most of the wathr ia removed by wsing t e fruit ’ over “ e f i a t o r s . “ These consist of brass rolls which collee the water and from tho bottom of which the wnwr w removed bv sauewee Dhtes. Hot air fans directlv above the moving fruit c&naeteuthe*dryitu, Gra fruit ie never coloied, except-for-the apparent coloring b r o u z about by the removal of chlorophyll with ethylene; oraneea ~ & 9 throueh s a colorinn bath between the wnasber and the
wid
~
~~~
~~~~~~~~~~~
%’
130” F. and &&a
of spraying thc fruit kith an oil-sbluble nontoxic dyc followed by a thorough brushing. D.veing and waxing are rally patented rocca8o8 and packiug plana pay considarable rovalties to w e tiem. EXWBDI~~ofsome dve ~rocemesare
Within the patent specifications the quantity of biphen 1 used may vary between 25 and 42 mg. per individual wrap. gecatwe of ambient qualitiee the biphenyl migrates to the skin of the fruit, protecting it agdnst “blue” and “green” molds. Other chemically treated wra have been the subject of patents (9) and research and Florida A y u l t u r d Experiment Station has experimcntedwiththeuof P iofilmaeafritwrap (2). After waxing and polishing the fruit is hand-graded, theqmac b i n d e d , and packed. It is on the grading tables tpBt the juice fruit is aorted from the fmt to be packed; t h results m an actud improvement in quality of the fruit heiig packed, since dl inferior fruit is removed at this stage.
(a)
tE
JUICE PLANT
Texsun’s juice p h t was first put into operation during the
1935-36 %?ason. Operation of the plsnt is necansarily seasonal and the period is ordinarily from about December ta June 10, lagging slightly behind the first packing operations because “quality” juice cannot be made from early fruit, owing to the high content of the bitter g l u 4 d c naringin (which decreases as the 8888011 advances) and the resulting distasteful flavor. ‘she juim fruit, as it is brought from the packing plants, is welghed in, dum d from trucks and lifted by bucket elevators to nrimarv mad% belts. Ve; inferior fruit. which includes “s ha” abd-moldFd specimens, is taken out b hand, and the fruit thus removed goes straight to the de&lmtion plant. The primary reaaon for m o v i n g t h cull f r i t is the great daneer of 8 ~ 0 i l a ~ becawe e. altboueh fruit is never held in the sto& bins’for % e than 24 hours,-one had piece will contaminstc other graded fruit in the bins., W n a m o . From the SOOton bum the f+t is passed to a final nradinc belt. whrrc additional idprior f r i t is removed bv hand:
CUE
I N D‘U s T R I A L A N D E N G I N E E R I N G C H E M.I s T R Y
March 1948
tiple purpose of soaking, washing, and oil control. This tank is fitted with steam spargers and temperature controls; the temy t w e can be adjusted at willand may vary during the season rom welltemperature (averageis 85”F.) up to a point just helow hoilina. Scott. in his article on Dretreatment of manefruit for juice & ~ h g(SS),diseuwes someof thv bases for a d j b d n g thia temperature. The main object of hot wawr treatment w control of the oil rontcnt. which ia arcomo~ishcd m result ofth@oil’s
the end of the season, but that the ascorbic acid content of Texas grapefruit and orangea is closely comparable to that of Florida and California. Ross (31, 38) and Lmnb (16) discuse the factors aEecting vitamin C content in citrus juices, and Moore (88) states that the average ascorbic acid retention of unsweetened grapefruit juices during commercial canning for twelve central Florida w i n g plants wm 97%. At the Texsun plant lass than 2% of vitamin Cis lost during processing of the juice.
are renboved in the hot pit. The tank also tends io “plump” t h r fruit. so that it will beeasier to handle i n suhcqucnt operations. Next in line of flow comes the “tank room.” consisting of six Thw far movement of the fruit has burn due to nrrssw of the jOOgallon open-top tanks, whose niaiu function is to act i s surge fruit behind: after 30 seconds in the tank the fruit is raised bv a tanks. In the early days of juiring nt the plant these tanks were screen paddlo wheel and ib: then passed over a series of bristle wed to mntrol the oil eondent. The iuice rends to foam some_.. .~ _ bruslrrs t u remove dirt and foreign arrieles. during which time it what, and at this point a laborer was stationed with a paddle to i, aorsved with cold. chlorinated l! _ LI.I).III. the can ~~, ~I water _ from ~ ~ ~~~. ~ ~skim ~ off ,the foam and the ail contained in it. With the advent of coolers: :During the washing operations considerable use is made droiling this operation was omirted. M i l e the juice is in the of detergents, including some of the quaternary -onium comurge tanks the acid and nrix ratios RIP checked (home trouble 1s pounds, sulfonates, ete., in concentrations of about 0.1%. exurrienced w i l l Texas maoefruit in eettinc enuunh acid 10 stkfv eovernment reanire&&te for Fa& G&e AI juice), sugar is ad&d if nceessary, and blending for Gifornuty ia carried out. A great deal of work has been done in Temn’s researeh labore Automatic flo\r,-proportioning haa h e n arrrrnpted in making tory to determine the detergents best suited for this operation, grapefruit-orauge julee blonds, but has not yrr I)eensuceesful. but results 80 far have not shown marked superiority in any one detergent. It is important in the packing plant that these comGovernment standards (@) for Fancy Grade A juice are as pounds have a fungicidal action to prevent spoilage, but in the follows: juice plant the main requirement is simply the eleansing of the Brix N o t >8.5 Aoid Not $1.0 p m nor >2.0 g a p $ (osloulated 88 anhrdroua fruit. I n all operations it is important, however, that the determtno wid) per 100 ml.,of juice gents used be nontoxic. Brk-acid ratio Brk value 6.6 x the acid value, minus a factor of 1.6: ~~~
~~~~~~~
~
~
~
~~
~~~~~
~~~~~~~~
~~
~~~~~
~~~~~
EXTRACTION. The cleaned. unsized fruit is lifted hv bucket ele-
vators t o the iusiilr of the juiw plant and conveyed on bello to tluer bunks of hi$h speed Uireloy Citromat extractors; t w o of thew banks con~ainr h r w cxlractors eacli and ono contains four. Such an arrangement makes the plant very versatile and permits not only processing oranges and grapefruit at the same time, but also low and high speed operation, Thus there can he produced o y j e juice or grapefruit juice or both, or orange jmce and a en or grapefruit juice and a hiend, at an operating speed of 50, 100 or 150 gallons per minute. ?he fruit is halved by sharp Circular knives and paasas between two drums 36 inches long and 20 inches in diameter, the front drum rotating twice as fastas the rear drum. The rear drum has short pegs whichgrab the rind, and long spikes on the front drum tear out the pulp and “rag.” There is sufficient clearance between the rollers to prevent squeezing of the rind. A squeegee on the hack of the rear drum scrapes off some of the citrus oil and it goes offwith the peel, which drops with the rag into a screw conveyer. A pneumatically operated screen at the bottom of the rear roller allows some pressing to take place and compensates for different thicknesses of peel. ~~~
~~~~~~~~~~~~~~~~~~~~~~
.~~~~~ ~~
~~
~~~~~~~~~~~~~
A conservative handling figure for each extractor is 12 tons per hour, which means a top daily capacity of 2400 tons,since the plant operates on a %hour basis. Operating in this fashion allows a &hour shutdown during every 24 hours for complete cleaning and sterihation of equipment. The juice per ton of fruit varies from a low of about So gallons per ton at the beginning of the s e w n to a maximum of 100 and then drops considerably toward the end of the s e m n when more and more inferior fruit is received at the packing plants, but the average is 90 gallons per tun, or 26.9 &wan. At 8.6 pounds per gallon this amounts to 775 pounds of juice, or an average of 40% juice and 60% peel and rag in the fruit.
From the extractors the juice paases to the finishing unit, which might best he described as a “mechanical colander.” This unit is very similarto the paddle-ty e pulper described in an earlier puhlication (18) and is esent&y a perforated (0.Ou) inch) screen cylinder with slow1 revolving longitudinal paddles. I n the finishing unit the see$, p i p , and segment membranes are removed from the juice and join the peel for transfer to the dehydrating unit. All equipment used in the juice plant is stainleas ateel or aluminum, since vitamin Cis catalytically oxidized by the presence of traces of iron or copper (7, 11). Metcalf (.til), in a study of vitamin C content of Valley citrus, points out that a d e h i t e reduction in ascorbic acid content in the fruit t & place ~ toward
ratio Br*-acid not t o eroeed 12 to 1. Recoverable oil Not >0.015% by volume (0.030% for oransee) Pulp Not >lo% free and suspended pulp
DEOILINO. Deoiling and deaeration constitute one of the most important steps in the entire juicing operation. Deoiling is important because the citrus oil (90% &limonene) belongs to the terpene family and imp& a turpentinelike flavor to the ~ ~ juice on storage. Canners throughout the industry a l consider oxygen removal important. Oxygen is objectionable because of its effect on the oxidation and polymerisation of citrus oils and on loas of vitamin C. I n the Dlant deoiling a i d deaeration are carried out in two Rufluvak iauuum unit{ with ori ‘nall designed capacitirn of 40 and60gallonsperminute whichfavcgeenxteppcdupb theuse of oversize conden*ersroLandlemmnchas6Oand 12Udlons Der minute. resnectivelv. The juiceisfedinatmint A on%ow shket (paw 372) bnd renioved at.point R, averak t h o of throughput tieing 4 IO 6 minuwn. In between these two points it has made a ~ l ~ n d of r r D R ~ R P R thnmnll the s t ~ a r nheater. throuah the flash rate of
1600gallo& per minute.
_. . .
The cold juice is hcatrd to within a few degrecs of 125’ F., depending 011 the V B C U l l N obtainahlc,witli rbe ,lifferenec between T Iand T,maintained at 4 ’ F. Bafflesare ernpliiyed in the flash vbanilw to cut down entrainment. The vacuum inlimited by the
374
INDUSTRIAL AND ENGINEERING CHEMISTRY
Liming Operation, Showing Hammer Mills, Lime Feed, a n d Peel-Lime Mixture in Pug Mill capacity of the steam-jet ejectors (which are in turn affected by the quantity of air to be removed) and by the temperature of the cooling water, but 26 inches of mercury are maintained as closely as possible. Since there is about 2% air in the juice to begin with, and more is added as it passes through the extractors and pumps, there is a considerable quantity (although this amount has never been determined) to be removed, passing out a t the point marked “noncondensables.” The actual temperatures represented by T I and Tzare not important, so long as they are within a few degrees of 125 O F.; the range can be 126 and 129 O F. or 128’ and 132 O F . , for example. During the time that other operating data were being taken for this paper, temperatures were in thelatter range. A difference of 1 between 2’1 and Tz results in the flashing of approximately 1% of the liquid; therefore about 4c%,of the liquid is flashed. The flashed vapors containing the oil are condensed and run into a decanter. Here the oil separates and is drawn off intermittently as a top layer and the aqueous phase is returned to the flash chamber. While at the top limit of operation such a unit can remove from 100 gallons of juice 0.055 gallon of oil and leave only 0.010 in the juice, the average is to start with juice having an oil content of 0.0227, and take it down to 0.005% oil.
Vol. 40, No. 3
combine the recycling and decanter system as does the Texsun plant. The Mojonnier deaerator-deoiler, used in several plants in Florida and Texas, is a single-pass system and one new system employs several small circulating pumps. The single-pass system is certainly a simpler method, but it means that the juice has to bc “burned” more-Le., there must be a greater difference between T I and 7’2-in order to get the same efficiency in oil removal. Another important point about the method used by Texsun is that the speed of input of the juice to the flash chamber can be varied according to the original oil content of the juice; if it is low thc amount of juice processed can be increased; if it is high the discharge pump can be slowed. No use is made of the citrus oil obtained a t this step, the only easily recoverable oil in the plant’s operations. From a volume standpoint the quantity of oil removed by the deoiler during a day’s run is not significant; it runs about 1 pint per 1000 gallons of juice processed, or a removal of about 27 gallons of oil per day at peak capacity. All this oil is being saved, however, for research operations. PASTEURIZIXG. The deoiled and deaerated juice is pasteurized in standard Chisholm-Ryder milk-type pasteurizers, where the juice is held a t 190-192” F. for approximately 1 minute. Three units with a capacity of approximately 200 gallons per minute are installed. The temperatures involved are higher than in the previous installation in the plant where the juice was run through stainless steel tubes for quick pasteurizing at about 180” F. Although the lower temperature was sufficient to destroy the microflora present in the juice, Lueck and Pilcher (18) point out the importance, since the advent of flash pasteurizing with its short time, of ensuring a sufficiently high temperature to inactivate the pectic enzymes. In discussing the work of Kertesz on enzyme action of the pectins, they show that it is imperative that the pasteurization inactivate these enzymes in addition to killing the bacteria. This inactivation is necessary to prevent the conversion of pectin to pectic acid and the separation of solids which would result during storage. Joslyn (14) discusses the effect of heating on citrus juices and Loeffler (16) states that cloud activity is increased by flash pasteurization and not merely stabliliaed. He also states that loss of cloud during storage is not due entirely to pectic enzymes. Phaff ($7) offers the explanation that a pectin esterase is involved, which breaks down the pectin, so that it no longer acts 8s a protective colloid t o prevent the settling out of solids in the freshly packed juice. No definite agreement seems to have been reached as yet in the industry on this point.
O
One of the very troublesome problems in connection with removal of citrus oil has been in the laboratory tests. At Texsun’s ordinary rate of production, use of the standard method (4%),which takes 1.5 hours to perform, means that more than 5000 cases of juice have been processed and stored in the warehouse before the test has been completed. The seriousness of this situation, in the event of an overly high content of oil, can readily be seen. A new turbidimetric method (6) has been worked out a t the Texsun research laboratory which uses a small sample, gives adequate control of the oil content, and takes only 7 to 8 minutes to perform. Most other methods of oil removal and deaeration used by juice plants in this country do not recycle the juice and do not
The juice is now ready for the cans. On page 371 is shown the fast can-filling machine for No, 3 special (46-ounce) cans, which handles 240 cans per minute. For the high-speed machine which handles the No. 2 cans, the greater portion of Texsun’s output, thz capacity is 360 cans per minute. These cans are filled a t 180-185 F., the lids are put on and closed, and the cans are inverted t o allow the hot juice to pasteurize the inside of the lids. They aic then carried by a sanitary belt to the can coolers where chlorinated water (7 p.p.m.) takes thetemperaturefrom 175 O F . down to less than 100”F. in approximately 2 minutes. From here the cans are labeled and boxed for shipment and storage. If a stoppage of the filling machines should occur for any reason, with a resulting drop in the temperature of the juice, there is no opportunity for the operator to continue filling the cans after hc has remedied the stoppage, if the temperature has fallen belov 180 O F. A thermostatic control is employed which forces the operator to dump the below-temperature juice and draw in a new batch before the machine can be operated again. This ensures adequate pasteurization and contol of subsequent can “swells.” SECTIONS
A very interesting small operation of Texsun is that of canning sections. Stevenson ($6)discusses canning of sections in detail. The grapefruit for this operation is put through a hot pit aiid held for 5 minutes. This plumps the rind so that it can be easily
March 1948
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
removed by hand. After the rind is removed, the fruit is sprayed with hot 2%lye (190” F.) which literally dissolves the remaining albedo and white pulpy portion surrounding the fruit. The fruit is then sprayed immediately with water to remove the lye and disintegrated membrane and goes to sectionizing tables. Here the sections are removed by hand using stainless steel knives, placed in stainless steel trays, and hand-packed in sweetened juice at 190O F. (Conditions are for No. 2 cans and would be slightly different for other sizes.) After being sealed, the cans are processed in a hot water cooker a t 190 O F. (185 O F. inside the can) for.18 minutes, passed through a cold water cooler for 18 minutes, and are stored for 2 weeks before labeling. This storage is necessary to firm the sections sufficiently to permit the rough tumbling of the labeling operation. From 28 to 30 cases of sections per ton of fruit are obtained. DEHYDRATING PLANT
i
As juicing operations became larger in the citrus industry, large tonnages of peel began to accumulate. At the beginning the companies paid to have the peel hauled away; now the general practice in processing plants is to bring in peel in addition to that which they produce. The capacity of Texsun’s juice plant is such, however, that no outside peel is required for efficient operation of its large dehydration plant. Even in the beginning the waste disposal problem was not as important in Texas as in some other areas. Because of the high lime content of the Valley soils *thewaste can be dumped on the groves as fertilizer; ip Florida it kills the groves. Members of the Texsun cooperative are allowed to buy the wet peel in certain instances for dumping on their groves; unless the peel is disked under, however, the odor presents a problem. [McNary (IO), Ratliff (% theI) Texas , State Department of Health (90), and Ingols (IS) discuss the problem of the treatment of canning plant wastes for disposal as sewage.] Besides use as a fertilizer, the principal (and only other significant) use is as a cattle food. After processing, the dried peel is either sold straight or mixed with citrus molasses. The process involves six steps: grinding, liming, mixing, curing, drying, and bagging. The peel and rag from the juice plant, which amount to about 1140 pounds from each ton of fruit, are stored in a 60ton receiving and storage bin from which they are fed to four hammer mills, each with a grinding capacity of 10 to 12 tons per hour. These hammer mills are kept operating at peak by controlling the amount of peel fed to them, so that a uniform power consumption is maintained. This the operator checks by means of ammeters on the hammer mills.
Dehydrating Plant Instrument Board and Sccond-Stage Dryer
375
LIMING. The liming step is an important one in the dehydrating process. A special lime formula is fed from a hopper through a variabledrive screw feed into the screw conveyer a t a rate of 10 to 12 pounds per ton of wet peel or approximately 0.5%. The mixing is done in ti pug miil, essentially a screw conveyer with half the screw blades cut away and the remainder angled to the shaft so as to force the material slowly along. Van Antwerpen (49) mentions that the Citro Dry plant in Florida depended entirely on the pug mill for aging and that the other Florida plants used only the storage bins; the present status of this part of the operation in Florida is not known, but Texsun incorporates both steps in its treating. The mixture is then carried by screw conveyers to a drag and lifted to the top of a battery of 24 wooden curing bins, each with a capacity of 10 tons. It takes about 15 minutes to filleach bin, and 5 additional minutes would probably suffice for the curing operation most of the time, but Texsun allows from half an hour to a full hour for curing, depending on how well the peel drains. The amount of lime added is adjusted so that the mixture has a pH of 5.8, under which condition the peel li uor will begin to drain as soon as it reaches the bin. Addition oythe lime is a difficult control problem, because the acid content of the peel varies, and therefore the amount of lime required to produce the specified pH of 5.8 is not constant. It is here that the experience of the operators in judging the color and certain other characteristics of the limed peel is very important. The lime does most of its work in the curing bins through slow diffusion, and the result is demethylation of the pectins with precipitation and coagulation. This splitting of methanol from the pectin is accomplished in two different ways, enzymatically and chemically, and is essentially hydrolysis. The demethylated pectin is coagulated by the presence of the lime and syneresis occurs in the jellied mass, sugar solution being lost with consequent breaking of the gel. Actually, the moisture content of the peel is reduced only from 83.0 to 81.75% by the drainage process, although the peel liquor constitutes about 20’%of the peel, because the liquor contains about 12% solids itself. Still, the amount of peel liquor draining from the bins averages 2000 gallons per hour. The chemical analysis of this peel liquor is very similar to that of press juice (26). The peel is dumped from the curing bins by removal of boards a t the bottom, the operator being called a “peel-puncher.” At this step in the operation the lime in the mixture again assumes importance, because the gel will not have Broken if insufficient lime was added and too much lime produces an alkaline gelatinous and sticky mass; either condition adds to the difficulty of kiln operation. DEWATERING. Texsun started its dehydrating plant in the 1939-40 season and that year processed and sold only 640 tons of feed. How the plant has grown can best be shown by comparing that figure with those of Table 11, noting the 100% increase in capacity which is expected to be available before the end of this
INDUSTRIAL AND ENGINEERING CHEMISTRY
370
TABLE111. FUEL, POWER,AND WATERREQUIDMENTS (Baaed upon processing 1400 tons of fruit dsib) Ton of Fruit Praaessed Water Washing and a n cooling Deoiiing and deaerating Multiple-effect evapor&m
292.3 gal. 466 gal. 456 gal.
GM Power h o m e Dehydrating plant Submerged burners Daily totab water steam Electricity GM
1.54 Ib./gal. juice 89.7 Ib./sal. mol-s
...
28.9 kwh. 492.8 ou. ft. 1071.4 CU. it. 178.6 OY. it. 1,685000
Per Unit of End Product
3.24 gal./gd. juice 5.07 gal./gd, i u e e 126.7 gal./gal. molassea
steam Juioe plant 142.9 Ib. Multiple-etrectevaporators 142.9 lb. Eleotriaity
-
I.
4oo:ooo E
40,500 kwh. 1.930.000 CY. it.
11 364 DU. k,yton finishad kead 49.6 CU. ft./gal. moIas8ea
... ... ... ...
wason, after installation of a complete new dehydrating plant, a mirror-image of the one in c u m t we. Screw-expeller preases were 6r8t employed in conjunction with kilns, but were finally discarded. Texsun found the press method difficultof operation, particularly if any gelatinous material was obtained, since it almost defies pressing. At the time T e r n was using presses the DommerDial production of citrus m o b s wm unknown, and a considerable disposal problem was presented by the peel liquor. There is mme opinion that from an engineering standpoint the
Vol. 40, No. 3
whole system of dehydrating citrus peel may have developed in reverse. Since it is much better economics to evaporate water from a liquid than from a solid, if chemical engineers had been called in by the citrus industry during the original work on dehydration they might have pressed all the moisture poasible out of the pulp, thrown it away, and concentrated on evaporating the peel liquor to molasses. As it is, the dehydration of citrus pulp for feed has been a going thing in Florida for more than a decade (43)and citrus molasses is very new (6). Of course, the more the pulp is pressed at the start, the leas fuel or s t e m will be required to dry it completely. A t the same time, the smaller is the quantity of feed that can be obtained from a given amount of peel, since a greater proportion of the solide is lost in the liquor. However, more can be fed through the drying stage at the same cost and with the same equipment. A fundamental limitation of the kiln is that it is only 50 to 60% efficient (compare the 96% efficiency of the submerged burners in citrus molasses production), and in the last analysis only a balance of a number of factors, constituting a very complicated engineering problem, oan provide the answer as to whether preaaing or kiln-drying, or both, is most economical. In T e r n , at least, the low coat of natural gas is an important factor. McNary (19) c o h the expense of drying without preliminsry pressing where fuel mts are relatively high, and ad& another important factor in Florida, where bumidity is fairly high-hat drying the feed. without preliminary pressing produces a hygroscopic feed which may absorb atmospheric moisture and finally become moldy. The drained peel from the bins is raiaed by belt conveyers to the top of tbe drying kilns, where a systemofscrewoonveyerspermite flexibility in feeding the kilns or cycling the peel back to the bins. The drying takes place in two stages, the first
Simplifid Flow Diagram and Material Balamee
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
March 1948
311
Dehydrating Plant Cyclones stage consisting of three identical paralld-flow, rotary kilns (simply iron drums containing baffles, and unlined), 60 feet long and 8 feet in diameter, direct-fired with natural gas a t 2400 to 2800 O F. The peel is heated to 255' F. and regulation iron-constantan thermocouples are used to control the temperature. Texsun perfected two-stage drying t o enable the production of a light-colored feed, as is common in Florida, without pressing. In the first stage the moisture content of 81.75% is reduced to 40%, and all the material from the three kilns in the first stage goes to the fourth kiln, which is operated at 200" F. There are some pitfalls in the kiln operation which must be very carefully watched: if the feed to the kilns is too wet, sticking is ex eri enced; if it is too dry the feed may be burned. With the sticiin; of wet peel there is a temperature drop, which throws all the kilns out of equilibrium. As insurance against either of the above difficulties certain storage bins are kept full of wet peel with the proper characteristics, so that a reserve will always be ready. The combined capacity of the first and second stages is 5.5 tons of finished product per hour, with a final moisture content of 4 to 5%. The discharge from the second stage is air-cooled in a small kiln, conveyed t o a weighing hopper, and bagged in 100-pound sacks. Two forms of feed are produced: fines, from the kiln cyclones; meal, obtained by screening; and the regular pulp which is bagged on an automatic scale. When molasses is. added to the feed, a high speed mixer is used and the bagging is done by hand. I n connection with any consideration of the relative advantages between pressing and kiln-drying, the question of characteristics of the finished feed always enters. Pulley (29) has some interesting comments concerning the changes of composition in dried citrus pulp brought about by changes in methods of drying. A comparison of average Florida feed with Texsun feed follows: O
5
Florida
Texaun
Protein Crude 6.00 5.50
F a t Crude 3.21 2.50
Fiber Crude 18.75 10.50
N-Free Extract 54 62
The Texsun finished pulp contains sodium, potassium, iron, and considerable calcium, and is of good alkalinity. Although five sixths of the vitamin C originally in the raw, unlimed pulp is lost during the drying process, the finished feed still contains 30 mg. of vitamin C per 100 grams of pulp, based on analysis by the method of Nelson and Somers (26). This is of particular interest to feed manufacturers who add citrus pulp to nonruminant feeds. Heid (12) has stated that meal from pressed residue is usually darker in color and denser in texture than that prepared by pressing. Texsun meal, in contrast, is light in color and fluffy in texture.
'
CITRUS MOLASSES PLANT
The first citrus molasses plant in this country was a Kuder plant
at Lake Alfred, Fla., which began operation about 1941. Peel liquor finally became such a disposal problem a t the Texsun plant that the waste had to be hauled away and dumped on the groves, a method still resorted to in emergencies and a t the request of members of the cooperative. In discussing the Citro Dry plant in 1941 Van Antwerpen (43) stated that its peel liquor was concentrated in a triple-effect evaporator and added back to the peel at the final drying stage. I n the 1945-46 season Texsun made its first installation, using conventional multiple-effect evaporators. As is usual in this step, a major problem was encountered in the scaling-up of the evaporators, the evaporating capacity dropping as much as 50% in 8 hours. This led Texsun to the investigation of submerged combustion evaporation, and the installation of h a r k submerged burners before the evaporators. The first burner was put into operation for a short time during the 1946-47 season, and its success is evidenced by the fact that it was necessary to clean the evaporators out with caustic about once each week. With the twin units in use for the 1947-48 season, plus better operation of the clarifier, no washing had been necessary up to mid-February. Texsun has the only citrus molasses plant in the country using the submerged combustion principle, and has patent applications pending on the process. The peelliquor from the curing tanks drains into a flume and is collected in a large cement pit, from which it is pumped over a vibrating screen which removes the pulp that has fallen in small amounts from the bins. The screened liquor then passes into the first of two Ozark submerged burner units. Each of these units, which are cone-bottomed, 8 feet in diameter and 16 feet tall, has a processing capacity of 2000 gallons of raw peel li uor per hour and a holding capacity of 1000 gallons. N a t u r j gas consumption for each is 100 cubic feet per minute and air is supplied by two 100-h.p. natural gas compressors using 80 cubic feet per minute of gas. An air-gas ratio of 9.6 to 1 is used in the burners themselves, which are 10 inches in diameter The liquor is treated in the first burner a t 190' F. for 30 minutes, 400 gallons of water per hour being evaporated. Efficiency of these submerged burner units is about 96%. I n this burner both concentration (to 15O Brix) and carbonation take place. The liquor then goes through a clarifier (continuous settler) and into the second burner where it is further concentrated a t the
318
INDUSTRIAL AND ENGINEERING CHEMISTRY
same temperature t o 22 O Brix and additional lime is added if the pH is too low or if additional clarification is necessary. If there is any excess lime in the peel liquor the burner immediately neutralizes it, precipitates it as calcium carbonate, and automatically adjusts the pH to about 6.0. The first burner precipitates mainly calcium citrate and calcium pectinates, owing to their inverted solubilities. Besides the elimination of the severe scaling effects which these compounds would otherwise cause, the removal of solids has proved very successful a t the Texsun plant in eliminating the foaming tendency of citrus molasses during storage. An additional advantage of submerged combustion evaporation is a pasteurization effect as the liquor goes through thefirst burner. The discharge from the second burner (22" Brix) goes t o a series of three tanks. each with a 15.000-gallon caDacitv. Some of the heat is retained here while moie s1u;dge is a1lbwed"to settle, giving a final clarification, and the liquor is siphoned off the top by means of a hose attached to a float. By this time it is ready to pass to the multiple-effect evaporators. The sludge from the clarifiers and the final settling tanks is fed back into the curing stage of the dehydrating plant. When pressing operations are employed more citrus oil is obtainable in the peel liquor, from which it is easily recovered during evaporation. The oil readily steam-distills and can be separated by decantation from the condensate produced in the evaporators. I n the Texsun plant the oil in the peel liquor is negligible and goes out through the submerged burner stacks. The double-effect evaporators are the very latest design and are backward-fed, Liquor from the submerged burners is fed t o the second effect, which has natural convection circulation and is operated under a 26-inch vacuum. It then passes to the first effect, where forced circulation is employed because of the high viscosity of the molasses, and the operation here is at a vacuum of 22 inches. The circulating pump is supplied with 125-pound steam, and the exhaust steam is fed t o the heat exchanger. SJ7hen the molasses leaves the evaporators it has a final concentration of 72 Brix and has much less viscosity for the corresponding degrees prix than when the calcium salts and suspended matter are left in. O
A clear citrus molasses of excellent quality is produced and Texsun now has sufficient evaporative capacity so that no liquor need be hauled away. PROSPECTS
The citrus industry in the Valley is still growing. R7hat the future holds is anybody's guess, and five years may possibly see an overproduction due to the groves planted during the war years. As far as Texsun is concerned, more emphasis will be placed in $he future on products other than fresh fruit. Texsun's research staff of chemists and chemical engineers is currently investigating such subjects as improvement of juice quality, the causes of off-flavor development, and prevention of changes in flavor which take place on pasteurization. Texsun as yet produces no concentrates, but is workihg on cheaper methods of production. The manufacture of concentrates is occupying considerable attention in the citrus industry today, and Morse (25) in discussing the subject of high-vacuum technology stated that the new plant of the Vacuum Foods Corporation a t Plymouth, Fla., probably represents the largest commercial application of high vacuum drying techniques. This plant produces orange juice powder and concentrates. Weber (46) in 1943 described a new plastic used for casketmaking developed from waste citrus peel and pulp, and Nolte (26) discussed the production of feed yeast and industrial alcohol from citrus press juice. I n a survey of present and possible utilization of citrus by-products, Heid (IO)listed as some of the products either actually produced or possible: ascorbic acid, vitamin P, provitamin A, galacturonic acid, hesperidin, naringin, p-coumaric acid, rhamnose, and phloroglucinol A detailed study is provided by Baier (4) on the manufacture, properties, and uses of citrus pectates, and Pulley (28) discussed the production of crude citrus pectates from grapefruit cannery wastes. The plant of the Universal Colloids Company at McAllen, Texas, is using an ion-exchange method for the recovery of pectins from citrus peel.
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Since grapefruit is the main type of citrus processed at Texsun, future projects there will be angled toward grapefruit products, and a complete research program to be undertaken on the processing of fresh fruit will include problems in washing, coloring, and waxing. Additional projects in view are investigations on frozen products, uses of limonene, and the effect of trace minerals in juices. And lastly, a project which assumes particular importance for the cattle lands of Texas, Texsun hopes to see in the future the development of pelletized feeds from citrus pulp for use on the range. LITERATURE CITED
(1) AgricuZtz~raZStatisfics, U. S. Dept. Agr., 1945,p. 166. (2) Anon., Sei. American, 166, 81 (1942). (3) Arnold, P. T. Dix, Becker, R . B., and Neal, W. M.,Univ. Fla. Agr. Expt. Sta., Bull. 354 (1941). (4) Baier, W. E., and 1\7ik30n,C. IT.,ISD.EXC. CHEM.,33,287-91 (1941). (5) Becker, R. B., et al., J . Dairg Sei., 25,735 (1942). (6) Burdick, E. M., A n a l . Chem., t o be published. (7) Chase, E. M., Von Loesecke, H . W., and Heid, J. L., U. S. Dept. Agr., Circ. 577, 5 (1940). (8) Coman, Dana, Proc. PZa. State Hort. Soc., 53, 97-8 (1940). (9) Farkas, Adalbert, U. S. Patent 2,265,522 (Dee. 9, 1942). (10) Heid, J. L., Citrus Ind., 26,No. 1, 11, 14-15,22 (1943). (11) Heid, J. L., Food Inds., 15,64 (1943). (12) Ibid., 17, 1479-83 (1945). (13) Ingols, R. S., Sewage Works J., 17, 320-9 (1945). (14) Joslyn, &I. A., and Sedky, Abdalla, Food Research, 5, 223-32 (1940). (15) Lamb, F. C., IND.EXG.CREX., 38,860-4 (1946). (16) Loeffler, H. J., Proc. Ins?. Food Technol., 29-36 (1941). (17) Longfield-Smith, Longfield (to Food Machinery Corp.), U. S Patent 2,324,407 (July 13, 1944). (18) Lueck, R. H., and Pilcher, R. TT., IND.ENG.CBEM.,33, 292 (1941). 119) McNarv. R. R.. Ibid.. 39. 625-7 (1947). (20j Metcalf,'Emily,' Rehm, Peggy, and %inters, J. W., Food Research, 5,223-40 (1940). (21) Mispley, R . G., and Barber, W. R. (to Crown-Zellerbach Corp.), U. S. Patent 2,173,453 (Sept. 19, 1940). (22) Moore, E. L., et al., Canner, 98,No. 9,24-6 (1944). (23) Morse, R . S., ISD.ENG. CHEM.,39,1064-71 (1947). (24) Nelson, E. K., and Mattern, H . H., Ibid., 26,634 (1934). (25) Nelson, W. L., and Somers, G. F., 1x11.ENG.CHEW, ANAL. ED., 17, 754 (1945). (26) Xolte, A. J., Von Loesecke, H. W.,and Pulley, G. N., IND. ENG. CHEM.,34,671 (1942). (27) Phaff, H. J., and Joslyn, M. A , , WaZZerstein Labs. Commun., 10. 133 11947). (28) Pulley, G. 'N., &toore, Edmin L., and Atkins, C. D., Food Inds., 16, 285 (1944). (29) Pulley, G. N., and Von Loesecke, H. W., Ibid., 12, KO.6, 62-3, 100-2 (1940). '(30) Ratliff, H. C., Proc. Tex. Water Works Sewage Short School, 21, 123-8 (1939). (31) Ross, Edwin, CitrusInd., 22,No. 8, 6,9, 12, (1941). (32) Ibid., 9,27-33 (1944). (33) Scott, W. C., Canner, 93, No. 18, 11 (1941). (34) Sharma, J. N. (to Food Machinery Corp.), U. S. Patent 2,211,390 (Aug. 13, 1941). (35) Shrader, J. H., and Johnson, A. H., IND.ENG. CHEW, 26, 869 (1934). (36) Stevenson, A. E., Ibid., 26,823 (1934)., (37) Taylor, J. J., Proc. Flu. State Hort. Soc., 53, 91-3 (1940). (38) Texas Agr. Expt. Sta., BUZZ. 562,5 (1938). (39) Tex. State Dept. Health Bur. Sanitary Eng., unnumbered pamphlet, 4 pp. (1940); U . S.Public Health Eng. Abs., 20, No. 9, 33 (1940). (40) U. S. Dept. Agr., Bur. d g r . Economics, Crop Report (Oct. 10, 1947). (41) U. S. DeDt. Am., Production and Marketing- Administration, Market New; Service (October 1947). (42) Ibid., Tentative Standards for Grades of Canned Grapefruit Juice (issued periodically). (43) Van Antwerpen, F. J., IND.ENG.CHEM.,33,1422 (1941). (44) Van der Plank, J. E., Rattray, J. M., and Van Wyk, G. F., J . Pomology Hort. Sei.,18, 135-44 (1940). (45) Weber, G. L., Pacific PZastics Mag., 1, No. 4-5, 5-6, 44-46 (1943). (46) Winston, J. R., IND. ENG. CHEM.,26, 762 (1934). RECEIVED January 3, 194s.
