October, 1931
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
content, as acetic acid, of 4.60 per cent, traces of ethyl alcohol, 3.67 grams of solids and 1.29 grams of ash in 100 cc., 0.97 gram or 75.2 per cent of this ash being soluble. hlash which is not completely ripe admixed to ripe mash causes the fermentation process to come to a standstill after some hours of slow fermentation. The motive is the presence of great amounts of salicylic acid in the pulp. Methanol
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derived from the pectin in the fruit is present in overripe mash. Unpasteurized mash always shows amyl alcohol in the fermented liquid, and during fermentation a strong ammoniacal odor denoting the bacterial activity on amino acids is experienced. The vinegar output is on an average about 74 per cent of the theoretical.
Quick-Freezing Citrus Fruit Juices and Other Fruit A Preliminary Report E. :M. Chace and H. D. Poore L.ABOKATORY OF F R Y I T 4 S D v I . . G E T I B L E
CIIEXISTRY,
B u R E ; , ~O F CHEMISTRY A S D SOILS, E. ROAD,Los ANGELES, C.ALIF.
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HE greatest progresh Kearly a thousand packages of fruit juices and other apple juice by sloiv freezing in p r e s e r v i n g food* fruit products have been frozen at temperatures well and separating the colicend u r i n g t h e past fenbelow -10" F. (-23.3" C.). Glasses and glass jars, trate f r o m t h e ice crystals decades has been in the fields with and without vacuum closure, cr0wn-P bottles, by means of c e n t r i f u g a l s . of canning and of cold storfricti0n-W tins, tightly sealed, and open tins have Cans containing 300 pounds been used. The air has been washed from some of of orange juice were frozen in age. u p to this time, the canned product has gone to the juices with carbon dioxide, and carbon dioxide has the ordinary comlnercial ice machines, 24 hours being albeen used to fill the head space of other packages. the consumer in the original container, in which it can be Samples have been s t ~ m dat 7 " F. ( - 13.9" c.)for nearly lowed for congealing. The kept f o r a n y r e a s o n a b l e 300 days, and then for 75 days a t 45' F. (7.2" C.) withcakes were broken downin an l e n g t h of t i m e . On t h e out spoilage and, in most cases, without seriously ice c r u s h e r a n d s p u n as other hand, cold storage has affecting the flavor. rapidly as possible in a centrifugal of the s u g a r - h o u s e usua'ly been used with food in bulk, which, after removal from cold storage, has been type. By tnice r e t r e e h g the concentrate obtained, asirup conplaced in the hands of the consumer as rapidly as possible taining as high as 60 per cent solids could be produced. Howfor immediate consumption. The improvements in refrigera- ever, the concentrate when diluted had neither the flavor nor tion, both in commercial establishments and in the home, the aroma of the original juice. After considering the cost have now made it possible for the retailer and the housewife of the operation and the quality of the product, the investigato maintain a temperature sufficiently low to keep many food tion was abandoned. Over more than a year ago, however, experiments in quick products over long periods of time. Some twenty years ago, the coldpack industry was started freezing a t from -10" to -50' F. (-23.3' to -45.6' C.) by the berry growers of the Korthwest, and it has developed were undertaken with citrus and other fruit products. The into a large and profitable business. After many attempts results obtained by packing the containers in Dry-Ice (solid to preserve berries in cold storage, methods have been de- carbon dioxide) were so satisfactory that a small freezer was veloped which place in the hands of the manufacturers of built in which a current of 30 per cent calcium chloride brine jams, jellies, and ice creams a superior frozen raw product was cooled by passing it over Dry-Ice bunkers. While a t a reasonable cost. When a few years ago the fish dealers theoretically solid carbon dioxide should produce a temof the Atlantic seaboard began placing frozen fish fillets on perature below -110" F. (-78.9' C.), the lower limit of the market the berry packers began experimenting with small temperature in this apparatus was controlled by the freezing packages of frozen berries for home consumption, and in 1929 point of the calcium chloride, which was around -54" F. 1,200,000 one-pound cartons of frozen berries were packed; (-47.8' C.). Recently a larger freezer has been constructed in 1930 the pack was increased to 1,900,000 carLons. The which is completely surrounded by solid carbon dioxide bunksuccess of these products has encouraged investigation in ers in such a way that the alcohol used in place of the calcium freezing other fruits and vegetables. Naturally the attention chloride brine can be maintained a t a temperature below of investigators has been drawn especially to those fruits and -80' F. (-62.2' C.). juices which could not be satisfactorily pasteurized by heat. Fruit juices (including orange, grapefruit, lemon, tangelo, Diehl (2, 3 ) , Birdseye ( I ) , Woodroof (9, IO), Telson and apple, pomegranate, and pineapple) have been frozen in Lang ( 7 ) , Joslyn and Marsh ( 5 ) , McConkie (6),Reynolds crown-cap bottles, in vacuum-closure glasses and glass (8), and others have reported their results in both scientific jars, and in tin cans. Grapefruit hearts, orange slices, pineand trade journals, as well as in official publications. Pack- apple slices, etc., have been frozen both in glass and in apes ranging in size from l / 4 Dound to 10 pounds have been tin. used, a n i temperatures ranging from 10" F. (-12.2' C.) to Preliminary Experhents -80' F. (-62.2' C.) have been tried. The interest of this laboratory in freezing citrus juices Preliminary experiments were carried out in which orange followed the work of Gore (4) in his attempts to concentrate juice was frozen in 8-ounce open Cans a t -500 F. (-45.60 c.). The juice was satisfactorily frozen in less than 30 minutes, IReceived M a y 14, 1931. * Food Research Division Contribution No. 108. a smooth-grained, uniformly frozen cake being obtained
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There was no apparent tendency for separation of ice crystals near the sides. The cakes were removed from the tins by dipping for a few seconds in warm water, wrapped in specially prepared paper, and placed in cold storage a t 0" F. (-17.8' (2.).
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15 20 25 30 35 Minutes Figure 1-Comparison of Cooling R a t e s of Grapef r u i t J u i c e i n Glass a n d T i n A-Next to glass in 8-ounce jar B -At center in 8-ounce jar C-CaCh bath for 8-ounce jar D-At center of 9.5.ounce can E-CaCh bath for 9.5-ounce can 5
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The juice was excellent in quality but deteriorated during storage. The deterioration was marked on the surface of the cakes and proceeded toward the center during the storage period until finally the whole cake was unsatisfactory in aroma, flavor, and appearance. At the end of 6 months, the juice from all parts of the cake was objectionable in flavor. I n all probability, therefore, it will be necessary to keep frozen citrus products out of contact with air. The juice of Washington Navel oranges often turns bitter within a few hours after it is taken from the fruit. -4quantity of such juice, when frozen in 7-ounce open tins a t temperatures below -10" F. (-23.3' C.) in 15 minutes or less, did not develop this bitter flavor while frozen. However, after being defrosted and allowed to stand in the open a t room temperature for 4 hours, the juice became characteristically bitter. When allowed to defrost in a cool storage chamber a t 45" F. (7.2" C.), the presence of the bitter flavor was not observed until the third day. The same juice not frozen and allowed to stand a t room temperature developed the bitter flavor in about 4 hours. Freezing in Bottles
Several fruit juices were quick-frozen in open crown-cap bottles of 4 and 6 ounce capacity. They were capped immediately after freezing. Both vacuum and carbon dioxide were used to remove dissolved gases from the juice, and the head space in some bottles was filled with carbon dioxide. In later experiments the bottles were closed before freezing. Lots were placed in cold storage a t 7' F. (-13.9' C.) and, after 377-392 days, were defrosted a t room temperature. The aroma and flavor of most of the products mere fairly satisfactory. The juice of the Washington Navel oranges was slightly bitter, but to an extent that would probably not haye been observed by the ordinary consumer. So far as could be determined organoleptically, there was little difference in flavor between the juice frozen without preliminary treatment and that from which the air had been removed by carbon dioxide. Excessive use of carbon dioxide had t o be avoided, however, owing to the off-flavor developed.
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FRICTION-TOP CANs-Fair success was attained in freezing orange slices and sections, with and without 20 per cent sirup, and grapefruit hearts with 50 per cent sirup in friction-top cans. Inspections were made a t the end of 49, 113, and 231 days. Most of the products were found to be in fairly satisfactory condition, especially the grapefruit hearts and orange slices. Those covered with sirup were better flavored than those with which no sirup was used. The fruit in cans filled with carbon dioxide retained the original flavor better than when such precautions were not taken. Juices frozen in these friction-top cans became solid in about 3 minutes. The flavor was not so satisfactory as that of the juice frozen in bottles, and the use of carbon dioxide seemed to have no advantage. GLASS CONTAINERS UNDER VAcuuM-Another set of experiments was made, using glass containers with vacuum closure of 25 to 27 inches (63.5 to 68.6 cm.). The jars were of 8, 10, and 12 ounce capacity; the glasses of 8 ounce. With the brine a t approximately -31" F. (-35' C.), the juices became solid in about 15 minutes, the grapefruit hearts, pineapple slices, etc., in about 30 minutes. The packages were evacuated and capped before being frozen. After they were stored a t 7" F. (-13.9' C.) for more than 250 days and then defrosted, practically all of the packages still retained 22 inches (55.9 cm.) of vacuum. The appearance and flavor of the products were generally satisfactory. Pineapple slices in 50 per cent sirup and sweetened pineapple juice had undergone practically no deterioration as to color or flavor. Both the slices and juice retained the flavor of the original fruit better than did commercially canned products. Grapefruit hearts in 50 per cent sirup and orange slices in 20 per cent sirup were uniformly good, both as to color and
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flavor. Navel orange juice developed a slightly bitter flavor but so slight as to pass unobserved by some of those who tasted the samples. This bitterness, however, increased rapidly after defrosting, indicating that it will not be possible to store defrosted Xavel orange juice at ice-box temperatures until this difficulty is overcome. Preparation of Fruit
The juice of citrus fruit was prepared by reaming out the pulp on a revolving cone. The juice was then screened, and
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T a b l e I--.4nalysis of Glass-Packed Frozen P r o d u c t s S t o r e d i n Ice Box a t ter B e i n g Defrosted WASHINGTON 7570 GRAPEFRUIT GRAPEFRCIT NAVEL ORANGEPOVEGRANATE A N D 25y0 POME-GRAPEFRUIT GRAPEFRUIT PISEAPPLE JUICE JUICE JVICE G R A N A T E JCICE HEARTS HEARTS SLICES 25-26 in. 26-26 in. 25-26 in. 25-26 in. 25-26 in. 25-26 in. Original vacuum. approx. (62;% (63.5-66 cm.) (63.5-66 cm.) (63.5-66 cm.) (63.5-66 c m . ) (63.5-66 cm.) ( 6 3 . 5 - 6 6 cm.) Brix, degrees, original product 23.0 14.0 20.3 22.6 .... .... .... Acid as citric, yo original product 1.53 0 93 1.07 1.44 .... .... .... 2 4 . 0 in. 2 2 . 5 in. .... .... .... Vacuum, after 5-day storage ( 6 0 . 9 6 cm.! (57.1: c m . ) .... .... .... Vacuum, after 27-day storage 1 9 . 0 in." .... 2 4 . 0 in. .... (48.26 cm.) ( 6 0 . 9 6 cm.) 14 5 in. 2 3 . 0 in, 2 0 . 5 in. 23.5in. 23 5 in. 2 1 . 5 in. Vacuum, after 75-day storage (::!2%m.) (36 83 cm.) (58.42 cm.) ( 5 2 . 0 7 cm.) ( 5 9 . 6 9 cm.) ( 5 9 , 6 9 cm.) (54.61 c m ) Brix, degrees, after 75-day storage 23 1 14.4 20 3 22 8 Acid as citric, % after 75-day storage 1 56 0 96 1.06 1.42 a After 43-day storage.
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the bottles were filled and placed in the brine as rapidly as possible. When slices and hearts were prepared. the fruit was dipped in boiling water in order to loosen the rinds and then in hot 2.5 per cent lye solution in order to assist in removing the rag which vias finally rubbed off or removed with a blunt knife. These methods are in common use in the preparation of grapefruit hearts in canneries. Pineapples were pared by hand, cored, and sliced.
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Figure 3 --Comparison of C o o l i n g R a t e s of S i r u p a n d Grapef r u i t in G l a s s A-Sirup
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5 minutes. The temperature of the walls, lionever, was not attained a t the center until nearly 35 minutes had elapsed. Figure 2 illustrates the difference in the rate of cooling between sirup containing pieces of fruit and juice containing no fruit, both in 8-ounce glass jars. The juice was frozen to the center in about 10 minutes, whereas the sirup did not freeze a t the center until about 35 minutes had elapsed. The juice and brine were a t about the same temperature in 44 minutes, but the temperature of the sirup surrounded by pieces of fruit did not reach the brine temperature until 83 minutes after it was placed in the bath. I n Figure 3 the differences in cooling rate between the inside of the grapefruit hearts and the surrounding sirup, both a t the center of the 8-ounce jar, are shown. The sirup froze in about 20 minutes and the sections of fruit about 7 minutes later. I n the latter the temperature remained nearly constant for several minutes and did not begin to fall rapidly again until 6 minutes after freezing started. The brine and the contents of the jars reached a comnion temperature in about 55 minutes. Figure 4 shows the differences in the cooling rate of grapefruit hearts in sirup in different parts of the jars. The temperature of the brine here is a little below that ordinarily obtained. The fruit nearest the walls of the glass froze in 7 minutes, whereas that a t the center took more than 25 minutes. It is to be noted that the fruit which cooled very rapidly showed little or no break in the temperature curve at the freezing point; the other, the rate of which was less rapid, held the same temperature for more than 2 minutes.
Temperature Measurements
During these experiments, some interesting data concerning the rate of cooling of juice, slices, and hearts were obtained. The temperatures of the calcium chloride brine were ascertained by thermometer readings, the bulb only being under the brine so that the readings can be considered as only approximately accurate. The temperatures of the contents of the containers were taken with copper-constantan thermocouples of single junction, connected to a millivoltmeter and a lamptype portable galvanometer. The reference junction was placed in a quart Dewar flask containing brine a t 17.6"to 14.0" F. (-8" to -10" C.). Readings were taken a t intervals of 1 or 2 minutes, and the curves shown in the figures were plotted from the data obtained. The temperatures of the brine were usually below -22" F. (-30" C.) and in one case, as shown in Figure 4, below -40" F. (-40" C,). The initial temperature of the juice or fruit was between 59' and 68" F. (15" and 20" C.). It is somewhat difficult to tell just when congealing of the juices began, as the break in the curve is slight, but citrus juices freeze a t about 27.5" F. (-2.5" C.). It is seen from Figure 1 that in 9.5-ounce tins, the center reached the freezing point in less than 2.5 minutes, whereas in glass more than 10 minutes elapsed before the center froze. The juice near the walls of the glass began freezing in about
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Figure 4-Comparison of C o o l i n g R a t e s of Grapefruit a t C e n t e r a n d n e a r Wall i n G l a s s A-Section of fruit next to glass B-Section of fruit at center C-CaCh bath
The data illustrated in Figure 5 show that the rates of cooling on pineapple slices in 40 per cent sirup are not greatly different from that of grapefruit hearts. The sirup freezes in about 15 minutes, the fruit in 25, when the brine is around -30' to -35" F. (-35" t o -37" C'.).
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Storage of Defrosted Products
In order to test the keeping quality of the defrosted products, samples [which had been stored a t 7" F. (-13.9' C.) for 300 days] were defrosted and placed in a chill room having temperatures of from 35.6" to 46.4" E'. (2" to 8" (3.). A summary of the results obtained is given in Table I 20
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changed. The juices in the friction-top cans did not ferment, and only a small amount of mold was observed. ilfter standing a t room temperature, however, the products packed in this way were not equal in flavor to those packed in glass. A later set of samples packed in 7-ounce cans with tight closure have been in cold storage for 120 days and so far are highly satisfactory. It is of course recognized that, although no special attempt was made to put up these products under aseptic conditions, it may be impossible to produce material with as satisfactory keeping quality under factory conditions. Conclusions
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After 75 days of this cool storage, the samples showed no marked signs of deterioration, the appearance and flavor of most of them being good. Four jars had developed some surface mold about 1.0 cm. in diameter, but still retained a fair flavor. Sedimentation seemed somewhat heavy, but shaking the packages dispersed the sediment satisfactorily. The juices in crown-cap bottles kept as well as that in jars, and several bottles were removed from the chill room after 36 days and kept at room temperature, 50" to 77" F. (10" to 25" C.) for 35 days, Slight amounts of mold but no signs of fermentation were visible. There was no pressure on any of the bottles, and analysis showed that the total solids and acid had not
Experiments do not show that replacing the air in the head space above the juices or washing out dissolved air with carbon dioxide has any marked effect on the flavor of the juices. Too much carbon dioxide in the juice gives it an off-flavor. With frozen fruits, a slight improvement was noted when carbon dioxide was used; this was marked when friction-top cans were used. Vacuum-packed fruits are better than the ordinary pack. Freezing can readily he carried out in crown-capped glass bottles, 4- or 8-ounce, before or after capping, and in 8-ounce glasses or 12-ounce glass jars, with or without vacuum. Open freezing and freezing in friction-top cans is not recommended unless special precautions are taken for storage out of contact with air. Literature Cited (1) Birdseye, C., IKD. ENc. CHEM.,21, 414, 5 i 3 (1929). (2) Diehl, H. C., U. S. Dept. Agr., Tech. Bull. 148 (1930). (3) Diehl, H. C., Magness, J. R . , Gross, C. R . , and Bonney, V. B . , Canning Age, 11, 217 (1930); Calif. Fruif N c s , 82, 4 (Nov. 1, 1930). (4) Gore, H. C., "Apple Sirup and Concentrated Cider: New Products for Utilizing Surplus and Cull Apples,'' U. S. Dept. Agr. Yearbook and Yearbook Separate 639 (1914). (5) Joslyn, M. A , , and Marsh, G L . , INO.ENG.CHEM.,22, 1192 (1930). (6) McConkie, J. E . , Calif. Fruif N e w s , 81, 5 (Feb. 22, 1930). ( i ) Nelson, P. R . , and Lang, C. W . , Food Znd., 2, 184 (1930). (8) Reynolds, E.S., Fruif Products J . and Am. Vinegar Znd., 10, 143 (1931). (9) Woodroof, J. G., Georgia Expt. Sta., Bull. 163 (1930). (10) Woodroof, J. G I and Bailey, J . E , Z $ i d . , 164 (1930).
Ethylene Treatment of Tomatoes' E. F. Kohman RESEAXCH LABORATORIES, NATIONAL CANNRRSASSOCIATION, WASHINGTON, D. C.
HE ethylene treatment of tomatoes, as well as other fruits, has been given a great deal of attention in scientific and popular literature. Little (2), after calling attention to the use of ethylene with oranges and lemons, says,,"Tomatoes, celery, bananas, and other fruits lend themselves to similar treatment to advantage, and we may even look forward to a time when melons will look even more like melons and taste less like squash." It has been reported by Harvey (I), and colored illustrations are given in substantiation of this, that ethylene tends to ripen the stem end of tomatoes first. Nature tends to ripen the blossom end first. It would be extremely valuable to have tomatoes ripen uniformly on both ends for canning purposes. It seemed logical that if ethylene ripens the stem end first, tomatoes picked when they are not fully ripened and then treated with ethylene gas should result in uniformly ripened tomatoes. Furthermore, if tomatoes could be picked before they are fully ripened, they would stand handling somewhat
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better, thus resulting in less broken and bruised tomatoes which are foci for bacterial, yeast, and mold infections. It should be clearly understood that by no known method of ripening, except on the vine, can a tomato be produced equal in quality to a tomato fully ripened on the vine. The advantage for canners in any artificial ripening system would be in avoiding certain damages in handling fully ripened fruit. It may be added, this is equally true of any method of distribution. The quoted statement by Little may therefore give an erroneous impression. A study was made of the effect of ethylcne gas on tomatoes during the tomato season in a canning factory. The temperature ranged from 75" to 80" F. (23.9"to 26.7" C,). To treat the tomatoes with ethylene, a battery of six ash cans, of about 5 cubic feet (0.14 cubic meter) in capacity, were used. These were air-tight except for the cover for which an airtight seal was secured with modeling clay. Through a tube soldered into the cover and carrying a rubber tube with pinchcock, a definite volume of ethylene could easily be introduced.
