10 



CIRCULAR 6 5 9, U. S. DEPARTMENT OF AGRICULTURE 



noted for the apples packed in the standard box and in the 1%-bushel 

 eastern crate, the packing in both cases, however, including liners 

 and pads as well as oiled wraps or shredded oiled paper. The eastern 

 crate contained 20 percent more apples and was the tighter package, 

 and aft'er 10 days the fruit in its center had cooled only 22°, while 

 that in the standard box had cooled 34°. 



The results shown in table 1 should not be interpreted to mean 

 that use of pads, liners, and other packing material is undesirable 

 but rather that these materials insulate the fruit and increase the 

 requirement for refrigeration if properly packed apples are to be 

 cooled a& quickly as is desirable. 



In view of the results shown in table 1 the question arises as to 

 what would be the effect of lowering the temperature of the air below 

 32° F. on the rate of cooling. This is done in precooling, which is 

 the term applied to the rapid lowering of the temperature of a com- 

 modity to any desired level. While apples are not commercially 

 precooled to the same extent as are peaches, pears, plums, and certain 

 other fruits, in many cases it would undoubtedly be beneficial to 

 precool them, Delicious in particular because it is so prone to become 

 mealy and overripe. Records of fruit temperatures, if taken in many 

 storages, would disclose that most of the fruit is not cooled to 32° 

 for several weeks after harvest. Meanwhile, the rate of ripening is 

 being arrested only in proportion to the rate of cooling. The slow 

 cooling is often due to lack of sufficient refrigerating capacity of the 

 cold-storage plant, but it may also be due to faulty stowage in the 

 room, particularly failure to leave space for air circulation through 

 the stacks and to spread out large receipts of warm fruit. 



The greater the difference between the temperatures of the com- 

 modity and of the cooling medium and the more rapid the rate of 

 air movement the more rapid the rate of cooling will be. However, 

 as the temperature of the commodity approaches that of the cooling 

 medium the rate drops off. These effects are shown in figure 3, which 

 presents data obtained in another series of experiments conducted in 

 the United States Department of Agriculture cold-storage laboratory 

 at Beltsville, Md. The records were taken in the top layer of pack- 

 ages held at 32° F. and stowed as they would be in commercial prac- 

 tice. In the middle of the stacks the rate of cooling was slower be- 



STILLAIR; LINER, PAD, AND SHREDDED OILED PAPER 

 STILL AIR; WITHOUT LINER, PAD, OR SHREDDED OILED PAPER 

 MOVING AIR; LINER, PAD, AND SHREDDED OILED PAPER 

 MOVING AIR; WITHOUT LINER, PAD, OR SHREDDED OILED PAPER 



12 24 36 48 60 72 84 96 108 120 132 144 156 168 



ELAPSED TIME (HOURS) 



Figtjke 3. — Rates of cooling of apples packed in bushel baskets and stored at 

 32° F. in still and in moving air. Velocity of the moving air was approxi- 

 mately 200 feet per minute. The thermometer was located in centermost 

 fruit in each container. 



