4 circular 74 0, u. s. department of agriculture 



Storage Temperatures 



Research by Magness and others (1/+) has shown that when apples 

 are stored at 40° F., the rate of ripening is about double that at 32°, 

 and at 60° the rate is about three times that at 40°. At 85° the soften- 

 ing and respiration rates have been found to be about double those 

 at 60°. At 30° about 25 percent longer time is required for apples 

 to ripen than at 32°. This emphasizes the importance of having the 

 cold storage designed to establish quickly and to maintain uniform 

 low temperatures. 



UNIFORMITY OF TEMPERATURE 



Uniformity of temperature relates both to its range on the thermom- 

 eter scale and to the maintenance of a like temperature throughout 

 a storage room. In some plants, cycles of compressor operation cause 

 a fluctuation of 2° to 4° F. in air temperatures. Slight fluctuation 

 does not injure fruit unless it is downward to a point resulting in 

 freezing or in low-temperature injury. Apples or pears exposed to a 

 temperature fluctuating from 30° to 34° will keep as long as if stored 

 at a constant temperature of 32°. If the fruit is stored at a uniform 

 temperature of 30°, however, its life may be lengthened by 25 per- 

 cent (14). 



Maintaining uniformity of temperature in all parts of a storage 

 room is more important than avoiding small fluctuations at a given 

 point. Fruit ripens faster when stored in a part of the room where 

 the temperature is continuously higher than in another part. This 

 frequently results in the mixing of overripe and prime fruit in ship- 

 ment, or it may result in undetected deterioration and decay of fruit 

 in inaccessible locations. 



The influence of the temperature of fruit on the rate of ripening 

 has special significance in cold-storage management. Apples at 70° F. 

 ripen as much in 1 day as they would at 30° in 10 days; a delay of 

 3 days in an orchard or in a warm packing shed may shorten their 

 storage life as much as 30 days even if they are then stored at 30°. 

 Storage temperatures recommended for various fruits are discussed 

 in Circular 278 {20). 



EFFECTS OF RAPID COOLING 



Apples and pears are not injured by too rapid cooling unless freez- 

 ing takes place or the fruit is susceptible to injury by low tempera- 

 ture occurring above the freezing point. Some low-temperature in- 

 juries of apples are discussed on pages 9 to 12. 



FREEZING IN STORAGE 



Because of the dissolved constituents in fruits and vegetables 

 (chiefly sugars and acids) the freezing points of these products are 

 appreciably below that of water. The average freezing point of apples 

 is 28.4° F. It ranges from as high as 29.7° to as low as 27.3° in some 

 of the summer varieties, but is between 28.0° and 29.0° for the prin- 

 cipal winter varieties that are stored. The freezing temperatures of 

 pears are slightly below those of apples. Average freezing tempera- 



