Xany conflicting statements have been published relative to the effect of rate of freezing on the quality of many frozen products. Recently, one of the authors (F.A.L.), in collaboration with others, Lee and Gortner (1949), Lee, Gortner, and Whiteombe (1949a), and Lee, Gortner, and Whiteombe (1946, described the effect of freezing rate on peas, snap beans, asparagus, lima beans, corn, spinach, strawberries, raspberries, and peaches. N o significant differences were observed that could be attributed to rate of freezing, except in the case of asparagus. This vegetable showed texture differences, but the differences were really significant only when extremes in the rate of freezing (that is. freezing in liquid air versus freezing in an insulated box) were contrasted.DuBois, Tressler, and Fenton (1940) concluded ". . . the more rapidly meat was frozen, the better was its all-around quality. However, the palatability of the roast which was frozen at the slowest rate was good; wheii cooked it was tender and juicy and of good flavor. " ( 1930, 1931) stated that phpico-chemical changes occurring in the frozen condition, rather than puncturing of cell walls by ice crystals, o r rupture of cells by expansion during freezing, was the basic explanation of the drip from thawed fish and meat. He added, after speaking about corrective treatment and drip : " l f these findings stand confirmed, the advantages of rapid freezing diminish somewhat in importance. " However, he noted that as the speed of freezing is diminished, the appearance of the resulting product undergoes a change. The same author noted (about meat) : ". . . at very slow speeds there is a marked translucence." Taylor
LUCTUATING temperatures due to many different condi-F tions may be encountered in the storage of frozen foods. Temporary breakdown of facilities or equipment, improper response of temperature controlling devices, excessive loads during freezing, lack of a separate compartment for freezing, and frequent opening of the cabinet (particularly a side-opening box) all may lead to a temporary rise in the temperature of the stored food.Statements in the literature (1, 3, 10) stress the point that temperature fluctuations should be minimized, either because excessive desiccation may result or because fluctuations may lead to excessive growth of ice crystals in the food. None of these statements is accompanied by data to prove that undue desiccation or crystal growth necessarily is encountered in such cases, or to prove that the food quality is appreciably impaired.Work a t Purdue ( 9 ) indicated that temperature fluctuation over the range -5" t o -15" F. was not deleterious to frozen pork. Workers at Minnesota (4) stated that for frozen fruits and vegetables, constant storage temperature is not important if the storage temperature is 5" F. or less. In their study, the temperature fluctuated from 0 " $0 -20" F. with no impairment in food quality in a 6-month period. DuBois and Colvin (8) studied ascorbic acid in frozen peaches subjected to smell temperature fluctuation three or four times daily, and reported that, as a result of fluctuating temperatures between 5" and -5" F., 50% of the originally added ascorbic acid was lost in 1 year, whereas like packs stored at a relatively constant temperature of 0" F. lost but 32% of the vitamin C during stomge. Their data, however, dispute the significance of this statement.If undesirable effects from varying temperatures are to be expected, they will be found in the freezing range above 0" F., the usually recommended storage temperature. Furthermore, this is the range most likely to be encountered in freezer cabinets or lockers subject t o temperature fluctuation. No data are at hand, to evaluate the effects on frozen food of temperature variations in the range of 0 " to 20 ' F. PROCEDURES STORAUE TEMPERATURES. Three conditions of storage were maintained. A standard temperature of 0 " * 2 " F. and a control of 10 " * 2 " F. were maintained as representing constant temperature conditions. A third freezer, equipped with two thermostatic control switches, was carried through a temperature cycle between 0" and 20' F. For 36 hours out of every &day period, the control was set at 20" F.; for the remainder of the period (108 hours), the other control, a t 0" F., was in operation. This cycle was such that the food temperature rose from 0 " to 20 " F. and remained there for several hours before again being lowered to 0 " F. The 6-day cycle was' automatically repeated during the entire course of the 1-year storage period. The cycle represents a magnitude and frequency of fluctuations that may be encountered during frozen food storage without actual exposure t o thawing. on Quality of Frozen ...
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