COOLIl*rG HOT-BOTTLED PASTEUEIZED MILK. 37 



than if the milk were cooled immediately to the same temperature. 

 In fact, in om* experiments, on a 30-crate basis, there was a marked 

 reduction in the bacterial numbers during the cooling period, 

 especially when the raw jnilk contained large numbers of bacteria 

 before pasteurization. From our experiments it seems that pas- 

 teurized milk can be cooled, on a commercial scale, from 145° F. 

 (62.8° C.) to 50° F. (10° C.) by means of forced-air cu-culation withm 

 three hours; consequently the process can be completed well within 

 the 5-hoiu- limit. In order to have a wide margin of safety and to 

 obtain the best results, we recommend that the cooling process be 

 started immediately after the hot pasteurized milk is bottled and 

 that it be completed witliin three hours. 



The cooling of milk is absolutely essential in order to restrain 

 bacterial growth, and we wish to emphasize the fact that the process 

 of cooling slowly does not eliminate the cooling process, but simply 

 makes use of a slower-coolmg process than is in use at the present 

 time. 



9. So far as our laboratory experiments on a 30-crate basis in- 

 dicate, slow coolmg of hot-bottled pasteurized milk has no appreciably 

 detrimental effect on the cream line and the flavor of the milk. This 

 is true for periods of cooling of not more than three hours. It is, 

 of course, possible that different results may be obtained on a large 

 commercial scale. 



10. On account of the uneven heating of pint and quart bottles 

 in similar positions, and the same-sized bottles m different position 

 in the stacks, attempts to heat milk in bottles by means of forced- 

 air circulation were not successful. It was found impossible to heat 

 the bottles to the pasteurizmg temperature of 145° F. (62.8 C.) 

 without overheating some of them. 



CONCLUSION. 



Our results indicate that it is commercially practicable to cool hot 

 pasteurized milk in containers not larger than quart bottles by forcing 

 cold air downward over them when the air is at a temperature of 40° 

 F. (4.4° C.) or lower. 



On account of overheating portions of the milk, the process of 

 pa.stcurizing milk in bottles by forcing hot air over them seems com- 

 mercially impracticable. 



This bulletin contains experimental data on the method of cooling 

 hot-bottled milk by forced-air circulation which we believe wiU bo 

 of assistance in tlu; practical apphcation of this method of cooling. 

 WTien the temperature of the outside air is 40° F. (4.4° C.) or lower, 

 it may bo used for this purpose, but when it is higher than that it 

 must b(^ (•()()]c(\ })y mcfhnmcn] rcifrigeration. It is possible to use a 

 combination of outside air and ndrigerated air; that is, outside air 



