PRECOOLING 



33 



In peaches which are shipped without wrapping, the cooling 

 is somewhat faster, but still is too slow to prevent excessive 

 deterioration with this more highly perishable fruit. 



In the recent work with vegetables, the cooling of hampers 

 of lettuce was found to be almost as slow as that of citrus 

 fruits which are wrapped and tightly packed. It is safe to 

 assume, therefore, that under ordinary shipping conditions 

 v^here the ice of the refrigerator car is depended upon to re- 

 duce the initial temperature of tightly packed crates of veget- 

 ables, the rate of cooling may be too slow to prevent the de- 

 velopment of the various diseases which affect the product 

 v^hile in transit. 



Precooling. 



In order to offset this slow cooling, a system of quick re- 

 frigeration before the produce is shipped has been developed. 

 This system has been termed "Precooling" from the fact that 

 the reduction of the initial temperature is accomplished quick- 

 ly and promptly either before the product is loaded in the car, 

 or after loading, but before the car begins to move on its 

 trip to market. The process consists simply in utilizing 

 special refrigerating facilities which will accomplish in a few 

 hours what it may require several days for the ice of the car 

 to do. 



In the case of produce loaded on the cars, the cooling is 

 accomplished by circulating a current of cold air through the 

 load until the produce is cooled to a temperature which the 

 ice in the car may maintain without difficulty. Naturally, a 

 number of mechanical problems have had to be solved in car- 

 rying out this work. 



Warehouse Precooling. 



The produce may also be cooled in ordinary cold storage 

 rooms before it is loaded into the car. In this system (known 

 as warehouse precooling) the packages are widely stacked in 

 order to allow free circulation between them. The refrigera- 

 tor rooms should be provided with extra refrigeration capa- 

 city to enable the work to be done quickly. 



For either of these processes the refrigerating medium 

 may be ice and salt, or mechanical plants working on usual 

 refrigeration machine principles. 



