2 CIRCULAR 4 47, U. S. DEPARTMENT OF AGRICULTURE 



these products are precooled — that is, rapidly cooled to a refrigerating 

 temperature, either immediately before or directly after they are 

 placed in the car for shipment, in order to delay maturity and conse- 

 quent deterioration. Where precooling is practiced, it is, of course, 

 essential to know the temperatures to which the product can be 

 lowered with absolute safety. 



It is also of great importance to the commercial cold-storage man 

 to know the exact freezing points of the fruits and vegetables that he 

 handles. Furthermore, knowledge of the freezing point of a com- 

 modity may be of special advantage to the warehouseman in case of 

 alleged freezing damage. In some instances established commercial- 

 storage practices have been changed after the exact freezing points of 

 certain products have been ascertained. In most cases fruits and 

 vegetables, other than dried or prepared products, when placed in 

 cold storage are alive, and the problem is to keep them alive and 

 healthy throughout their storage period. 2 As various fruits and 

 vegetables freeze at different temperatures, there is often more or less 

 doubt as to the proper and safe temperatures at which to hold them 

 while in transit or in storage. One of the problems in the storage of 

 many products is to hold them at a temperature low enough to slow 

 down the life processes, in order to prolong their storage life and yet 

 not allow them to be damaged by chilling or by actual freezing, either 

 of which is likely to injure their keeping qualities or market value. 

 For many products the optimum storage temperature is only 1° or 

 2° F. above the actual freezing point. In view of the above observa- 

 tions and the danger of uneven storage-room temperatures, a safety 

 margin of at least 2° above the freezing point should be maintained. 

 Of course some products, such as cherries, strawberries, peas, and lima 

 beans, may be purposely kept in a frozen condition below freezing 

 temperature, but this subject comes under the head of freezing 

 storage and will not be discussed here. 



Although it is important to know the freezing point of a com- 

 modity, it should be borne in mind that freezing or freezing injury 

 does not always occur when the fruits or vegetables are exposed to 

 temperatures at or below their true freezing points. This is shown in 

 investigations on potatoes, previously reported, 3 in which tubers were 

 cooled as much as 10° F. below their freezing point without actually 

 having become frozen and were again warmed up without apparent 

 injury. It is also commonly known that some kinds of products may 

 be actually frozen and then thawed out under certain conditions with 

 no apparent injurious effects. On the other hand, certain commodi- 

 ties, such as tomatoes, bananas, and cucumbers, are definitely injured 

 if stored at temperatures many degrees above their actual freezing- 

 points. This is usually termed chilling injury. 4 It is evident, there- 



2 For a discussion of the recommended storage conditions for various fruits and vegetables, see Rose, 

 Dean H., Wright, R. C, and Whiteman, T. M. the commercial storage of fruits, vegetables, and 

 florists' stocks. U. S. Dept. Agr. Cir. 278. 



3 Wright, R. C, and Taylor, G. F. freezing injury to potatoes when undercooled. U. S. 

 Dept. Agr. Bui. 916, 15 pp., illus. 1921. 



4 For a fuller discussion of chilling see Wright, R. C. low-temperatuke effects on the physiology 

 of plant organs in relation to commercial storage. Ice and Refrigeration, vol. 97, No. 4, pp. 2G1 264, 

 Oct. 1939. 



