28 CIRCULAR 713, U. S. DEPARTMENT OF AGRICULTURE 



side of the most exposed roots began in about 2 hours. At a depth 

 of three-quarters inch it did not begin until after 7 hours. After 

 24 hours at 25° the most exposed heads of cabbage (example 7, 

 p. 27) were frozen to a depth of one-half to three-quarters inch but 

 the heads at the center of the basket were still unfrozen. After 24, 

 hours all the rutabagas were frozen solid. 



It should be remembered that in all the examples given, the test 

 lot consisted of only one or two commercial packages. Under such 

 circumstances the rate of cooling would be more rapid than in the 

 interior of a stack of packages equivalent to a truckload or a half 

 or a whole carload. The rates of cooling shown are about what 

 could be expected in the outside packages of large stacks or blocks. 



The difference shown in figure 3, namely that cabbage, except 

 for the outermost leaves of exposed heads, froze much more slowly 

 than rutabagas, probably depended directly on a difference in the 

 physical characteristics of the two vegetables. The cabbage heads 

 were loose and were therefore protected internally by the insulat- 

 ing effect of numerous air spaces between the leaves. Rutabagas 

 are solid and therefore without protective internal air spaces. 

 Another important difference between the two vegetables is that 

 cabbage produces heat more rapidly (respires more rapidly) than 

 rutabagas. This extra heat in containers packed with cabbage 

 would give added protection against freezing. 



A slow rate of freezing similar to that observed in cabbage has 

 been noted in masses of lettuce and spinach in crates or baskets 

 and to some extent in other leafy vegetables and in peas and snap 

 beans in hampers or baskets. The reasons for the retardation of 

 freezing in all these instances are undoubtedly those mentioned 

 for cabbage — air spaces within the mass of packed produce and a 

 rather high rate of production of heat by the produce. 



In the consideration of examples 6, 7, and 8 an important fact to 

 be noted is that the cooler the vegetables when placed in the freez- 

 ing room the sooner they froze. This important fact must always 

 be kept in mind by those concerned with the handling and protec- 

 tion of fruits and vegetables that are likely to be subjected to 

 freezing temperatures. 



FREEZING NOT ALWAYS INJURIOUS TO PRODUCE 



At this point a word of caution is necessary. It should not be 

 assumed that produce is ruined and must be counted a total loss 

 merely because it is found frozen. Much depends on (1) what the 

 produce is, (2) how low its temperature goes during the freezing 

 period, (3) how long it remains frozen, and (4) how it is handled 

 after freezing occurs. Suggestions concerning this last point will 

 be found on page 3. (See also pages 2 and 4.) Careful attention 

 to them should result in saving produce that otherwise might be 

 thrown away or unjustifiably sacrificed on the market. Informa- 

 tion on items 2 and 3 may not always be available, but if it is it 

 should be taken into consideration. As stated previously (p. 2). 

 hard freezing, say at a temperature of 15° to 18° F., is more in- 

 jurious than freezing at a temperature only slightly below the 

 freezing point of the produce, especially if the low temperature is 



