38 BULLETIISr 420^ U. S. DEPARTMENT OF AGEICULTURE. 



at a temperature of, say, 60° or even 70° F. (15.5° to 21.1° C.) may 

 be used to cool the milk partly, the remainder of the cooling being 

 done by mechanical refrigeration. It should be noted, however, 

 that in coohng milk on a large scale by this method some unforeseen 

 difficulties may arise which we did not encounter in our experiments. 



This process of cooling by forced-air circulation, if commercially 

 practicable, could be appHed to advantage for cooling hot-bottled 

 pasteurized milk. Briefly stated, the complete pasteurizing and 

 cooling process could then be as follows : 



Milk could be pasteurized by the ordinary, holder system at 145° F. 

 for 30 minutes. It could then be bottled hot in special oversized 

 mil k bottles of the ordinary type and capped with ordinary sterile 

 caps. Before being filled, the bottles could be steamed for two 

 minutes by running the crates inverted on a conveyer over steam 

 jets; the bottles would then go through the bottling machine in a 

 hot condition and would be practically sterile. The crates of hot- 

 bottled pasteurized milk could then be cooled by stacking in a 

 refrigerator room and blowing cold air through the crates. In the 

 cold season outside air could be used for cooling, and in the warm 

 season refrigerated air could be circulated through the crates. 



This process could be modified in two ways: The hot milk could 

 be held in the bottles at 145° F. instead of in a tank, and the crates 

 of hot pasteurized nulk could be cooled by spraying with cold water 

 instead of air. ' ^ 



From a sanitary point of view the important advantage of the 

 process of bottling hot pasteurized milk in hot bottles lies in the fact 

 that bottle infection is efiminated, and if the bottles of hot milk can 

 be cooled successfully by forced-air circulation, the process of pas- 

 teurization would be raised to its highest state of efiiciency by 

 relatively simple methods. 



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