12 CIRCULAR 93 5, U. S. DEPARTMENT OF AGRICULTURE 



Cooling Rate and Storage Temperature 



It is generally known that rapid cooling after harvest and main- 

 tenance of fruit temperature at approximately 31° F. add considerably 

 to the storage life of apples. 



The air temperatures at the center of the packed boxes of apples 

 were recorded by using Ryan thermographs (fig. 1). Id these tests, 



75 



70 

 65 



~ 60 

 u." 



50 

 45 

 40 

 35 

 30 

 25 



BOX A 



\ 



J BOX B 



{I BOX C 



-n— 



1- 



rv 



I 1 I ! 1 1 1 1 1 I I 1 1 I 1 I I 11 1 1 1 I I i I 1 1 1 



3 5 7 9 II 13 15 17 19 21 23 25 27 29 



DAYS 

 Figure 1. — Air-temperature records at center of packed boxes of bruised and 

 inoculated Delicious apples harvested in 1949: Box A cooled slowly and reached 

 35° F. the 15th day; boxes B and C cooled rapidly and reached 32° the 5th 

 and 4th days, respectively. 



box B was held in the laboratory cold storage during the entire test, 

 while boxes A and C were stored in commercial apple storage rooms 

 for the first 29 days of the test and were then transferred to the 

 laboratory storage for the rest of the storage period. 



Boxes B and C cooled rapidly at similar rates (fig. 1), but the 

 temperature in box C held uniformly at 32° F. during most of the 29- 

 day storage period, dropping in two instances to a minimum of 31°; 

 whereas that for box B fluctuated generally between 32° and 34°, 

 dropping once to a minimum of 31°. Box A, in contrast, cooled much 

 more slowly and reached a 35° minimum temperature on the 15th 

 day, while boxes B and C reached a 32° temperature after 5 and 4 

 days, respectively. 



These temperature differences strikingly affected inception of blue 

 mold decay on the bruised areas of the apples (table 8) . At the first 

 inspection, 33 percent of the bruises in box A were decayed in contrast 

 to 8 and 1 percent, respectively, of those in boxes B and C. At the 

 second inspection, 2 weeks later, 51 percent of the bruises in box A 



