10 



CIRCULAR 659, U. S. DEPARTMENT OF AGRICULTURE 



are reversed. In cold storage the heat is transferred from the air sur- 

 rounding the fruit to refrigerated pipes or other artificially cooled sur- 

 faces and eventually is transferred to the outside air by the refrigeration 

 system (11). 



Cooling fruit ordinarily is not a rapid process, nor is ripening checked 

 instantaneously when fruit is placed in cold storage. Time is needed to 

 remove the heat from the fruit; the rate of cooling is affected not only 

 by the temperature but also by the type of package, the method of pack- 

 ing, the quantity of warm fruit placed in the room, the manner in which 

 the packages are stacked, and the rate of air circulation around the fruit. 

 Tests were conducted at the cold-storage laboratory of the Bureau of 

 Plant Industry, Soils, and Agricultural Engineering, Beltsville, Md., 

 to determine the influence of the type of package on the rate of cooling. 

 The temperature records were taken at the core of an apple at the center 

 of each package. The packages were not stacked and, : being freely ex- 

 posed on all sides, cooled faster than they would under commercial 

 storage. 



The results (table 1) show that the use of liners, cushions, and paper 

 for packing slows the rate of cooling. Apples in an open bushel basket 

 just as they came from the orchard, without liners, wraps, or shredded 

 oiled paper, cooled from 63° to 32° F. in 18 hours, whereas fruit packed 

 in lined baskets with a pad under the lid and shredded oiled paper well 

 distributed throughout required about 10 days to cool from 70° to 32.5°. 

 The relative thickness of the containers doubtless had an effect on the 

 rate of cooling, but the size of the package, or the mass of fruit enclosed, 

 and the tightness of closure apparently were important factors also, as 

 shown by a comparison of the results for apples packed in the barrel 

 with those for apples in the open bushel basket. It took only 18 hours 

 to cool the fruit in the middle of the bushel basket from 63° to 32°, but 

 it took 10 days to cool that in the middle of the 3-bushel barrel from 66° 

 to 36°. Similar results were obtained with the apples packed in the 

 standard box and in the l^-bushel eastern crate; the packing in both 



Table 1. — Influence of method of packing and storing apples in unstacked 

 individual packages on their rate of cooling at 32° F. in still air 





Packing material 



Temperature at core of apple in center 

 of package — 



Package 



When 

 stored 



After 



12 

 hours 



After 



18 

 hours 



After 



72 

 hours 



After 



7 

 days 



After 



10 

 days 



Bushel basket 



None 



°F. 

 63 

 70 



66 

 71 



66 



°F. 



42 

 59 



64 

 67 



63 



°F. 

 32 

 44.5 



59 

 60 



61 



°F. 



°F. 



°F. 



Do 



Liner, cushion, shred- 

 ded oiled paper. 

 None 



41 



55 

 54 



59 



33.5 



41 

 41.5 



54 



32.5 



Barrel 



36 



Standard box 



1 K-bushel east- 

 ern crate. 



Liner, cushion, oiled 

 wraps. 



Liner, cushion, shred- 

 ded oiled paper. 



37 



44 



