METHODS OF REDUCING THE GERM CONTENT 



525 



it is necessary, in addition to providing water-tight caps on per- 

 fect bottles, to allow for the expansion of heated milk. The 

 authors found the amount of expansion to be about 0.62 ounce 

 for 1 quart of milk. Therefore bottles for this purpose should 

 be made somewhat larger than modern bottles, permitting the 

 air space to care for the increased volume during heating. 



It was also found that the temperature in a bottle was not 

 uniform. When the temperature at the top was 145° F., it took 

 ten and four-fifths minutes longer for the temperatiue at the 



Fig. 214. — Front view of 48-case (576-quart) Cauffman pasteurizer. 



bottom to reach 140° F. Therefore, a period of exposure should 

 be calculated from the time the temperature at the bottom of 

 the bottles reaches the desired degree. 



In a series of 34 tests made by Ayers and Johnson the bac- 

 terial efficiency of milk pasteurized in bottles averaged 90.86 per 

 cent., varying from 17.67 to 99.98 per cent. 



Comparing the bacterial efficiency of pasteurizing in bulk and 

 filling in hot steamed bottles with that of pasteurizing in bottles, 

 ihe authors obtained the following average results : 



