PASTEURIZING MILK. 



17 



cool air against the bottle, heat would constantly be given up with 

 more rapidity by the milk and the cooling process hastened. In figure 

 8 are shown the temperatures in three bottles of milk cooled for 30 

 minutes in air. One bottle was cooled in still air at 77° F., one was 

 cooled in an air blast from an electric fan at a temperature of 77° F., 

 and one was cooled in still air at 35° F. At the beginning of the 

 cooling the temperature of the milk was about 145° F. As will be 

 seen from the curves, after 30 minutes' cooling the temperature of the 

 milk in the bottle cooled in still air at 77° F. was about 127.5° F., 

 while that of the milk cooled in an air blast at 77° F. was about 

 102° F. It is noted that by cooling in an air blast for 30 minutes 



IO 12 14 l6 l8 20 22 24 



Cooling period in minutes. 

 Fig. 8. — Effect of cooling a quart bottle of milk in still air and in an air blast. 



there was a reduction in temperature of about 25.5° F. in excess of 

 that obtained under the same conditions in still air. The temperature 

 curve of the milk in the bottle cooled in still air at 35° F. follows 

 closely that of the milk cooled in still air at 77° F. It is also inter- 

 esting to note that after cooling for 30 minutes in still air at 35° F. 

 the temperature was 122° F., while that of the milk cooled in an air 

 blast at 77° F. was about 102° F., a difference of 20° F. 



Since these experiments indicated that hot bottled milk might be 

 cooled more rapidly by using a blast of cold air, another experiment 

 was conducted in which one quart and one pint bottle were cooled in 

 still air which averaged 39.4° F. and another set in an air blast the 

 temperature of which averaged 44.3° F. The blast of cold air was 

 obtained by placing an electric fan in a refrigerator. The fan de- 



