2 CIRCULAR 713, U. S. DEPARTMENT OF AGRICULTURE 



SEVERITY OF INJURY DEPENDENT ON TEMPERATURE 

 AND ITS DURATION 



Problems that arise in connection with the protection of fruits 

 and vegetables against freezing and with the care of these com- 

 modities when they have frozen can be solved more intelligently if 

 a few fundamental principles are understood and used as guides in 

 handling produce. 



Fruits and vegetables do not freeze immediately when exposed 

 to a freezing temperature, and many of them are not immediately 

 injured even if they do freeze. Much depends on what fruit or 

 vegetable is concerned, on how low the temperature goes, and on 

 how long the product is exposed to the dangerous condition. Pota- 

 toes and tomatoes are injured if any ice forms in their tissues even 

 though the exposure is very brief and the temperature barely 

 reaches their freezing points. In this respect they resemble sweet- 

 potatoes and other products listed on page 30 in the group most 

 susceptible to cold or freezing injury. 



On the other hand, apples, cabbage, carrots, and other produce 

 in the groups moderately susceptible or least susceptible to freez- 

 ing injury (p. 30) are injured very little by exposure to tempera- 

 tures only a few degrees below their freezing points, whereas at 

 temperatures below about 20° F. they are in much greater danger. 

 However, if these two different sets of conditions are assumed, the 

 time element becomes of the utmost importance. Apples exposed 

 to 25°, say for only a few hours, will be damaged very little if at 

 all, whereas if they remain at that temperature for 3 or 4 days 

 they may be so softened and otherwise injured that their keeping 

 quality is seriously impaired. At 15° to 18°, however, they may be 

 damaged as much in 12 to 15 hours as they would be at 25° to 27° 

 in 3 or 4 days. If held at the lower temperature (15° to 18°) for 

 several days, they become "frozen to death" and worthless. Simi- 

 lar statements are true for numerous other products in the mod- 

 erately and least susceptible groups. 



The important fact in the preceding discussion is that for any 

 given product the combination of time and temperature determines 

 the severity of injury. Enough time must elapse for the forma- 

 tion of ice in the tissues ; and, for reasons that are not well under- 

 stood, enough more time must elapse so that the tissues suffer in- 

 jury from which they cannot recover. The lower the temperature 

 the shorter the dangerous, critical period. The length of this 

 period varies with different products, but its significance and 

 importance should always be kept in mind. 



METHODS OF PROTECTING FRESH FRUITS AND 

 VEGETABLES AGAINST FREEZING 



Methods of protecting fresh fruits and vegetables while in cold 

 storage or on the way to market are fairly well known, although 

 they are not always used intelligently or with full appreciation of 

 the risks involved if they are not used. 



Sometimes these perishable products are held in storage at too 

 low temperatures or in rooms where the temperature occasionally 



