532 



MILK 



teurization at 76.7 C. (170 F.) there is little change in the rela- 

 tion of the acid group, but the peptonizing group begins to in- 

 crease. This increase is continued as the pasteurization tempera- 

 ture is raised. When milk is pasteurized at 82.2 C. (180 F.) 

 peptonizing bacteria are predominant and continue to predomi- 

 nate at still higher temperatures. 



30 



76.7C. 82.2C. 87.8C. 



.. 



(200"*} 



Fig. 216. The hypothetic relations of the bacterial groups in raw and pas- 

 teurized milk. (Ayers and Johnson, Bull. 161, Bureau of Animal Industry, 

 U. S. Dept. of Agriculture.) 



As long as the pasteurization temperature is not higher than 

 76.7 C. (170 F.) acid-producing organisms predominate. When 

 higher temperatures are applied the acid group is largely destroyed 

 and peptonizing bacteria predominate. The percentage of lactic 

 acid bacteria surviving pasteurization in different kinds of milk 

 varies from 1.27 to 4.55 per cent. 



When milk is pasteurized at 62.8 C. (145 F.) for thirty 

 minutes and then kept at room temperature the changes pro- 



