18. 



BULLETIN 240, U. S. DEPARTMENT OF AGRICULTURE. 



livered air at a velocity of about 1,250 feet per minute. The tem- 

 perature curves in figure 9 show the results of this experiment. The 

 temperatures of the hot milk at the beginning of the cooling ranged 

 from 140° to about 143.5° F. in the different bottles. It will be seen 

 from the curves that five and one-half hours were required for the 

 temperature of the quart bottle of milk in still air to reach 50° F., 

 while the milk in a quart bottle in an air blast was cooled to 50° F. in 

 a little over two hours. The milk in the pint bottle cooled in still air 

 reached a temperature of 50° F. after about three and one-half hours, 

 while only one and one-half hours were required to cool the milk 

 in the pint bottle which was in a blast of cold air. 



From these results there can be no doubt as to the value of an air 

 blast for cooling bottles of hot milk, at least as compared with still 

 air as a cooling medium. As these experiments were made on single 



iso°F. 

 140° F. 

 130° F. 



120° F. 

 no°F. 

 ioo°F. 



go°F. 



80° F. 



7o°F. 



6o°F. 



50° F. 



40° F. 



Fig. 9. 



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Cooling period in hours. 



-The cooling of pint and quart bottles of hot milk in still air and in an air blast at 

 refrigerator temperature. 



bottles it was thought advisable to try cooling several crates of 

 bottled hot milk by an air blast. Specially constructed skeleton- 

 frame steel crates were used, so as to allow a free circulation of air. 1 

 Milk was pasteurized at 145° F. for 30 minutes and bottled hot in 

 ordinary milk bottles by the aid of a hand bottle filler. The bottles 

 were then capped with the ordinary cardboard caps and placed in 

 crates. Four crates were used in these experiments, two filled with 

 quart and two with pint bottles. The two crates which contained 

 quart bottles were placed in a refrigerator room one above the other, 

 and directly back of them were placed the two crates of pint bottles 

 one above the other. The air blast was generated by a 16-incli desk 



1 Mr. John T. Bowcn, of this division, assisted in this work. 



