518 



MILK 



customers believed the milk had been skimmed. It is natural, 

 therefore, that the temperature for flash pasteurization was 

 gradually reduced, until at present the average temperature prac- 

 tised in this country is 71.1° C. (160° F.). This temperature 

 cannot be depended upon to destroy all pathogenic bacteria, al- 

 though it results in a material reduction of bacteria. There are, 

 then, two objections to flash pasteurization at 160° F.: 1, apparent 

 reduction of the quantity of cream, and 2, uncertainty as to the 

 destruction of pathogenic bacteria. 



ttroma strr i* 



Fig. 206. — ^A regenerative pasteurizer for use with holding tank. (S. H. Ayera 

 in Circular 184, Bureau of Animal Industry, U. S. Dept. of Agriculture.) 



2. The holding process overcomes these difficulties in large 

 measure. The holding or held process, as originally designed, 

 means that the milk is heated to 60° C. (140° F.), held at this 

 temperature for twenty minutes, and finally cooled. The cream 

 line is not appreciably affected, and the temperature and period 

 of exposure are sufficient to destroy pathogenic bacteria. 



In laboratory experiments the holding process has proved to 

 be efficient when the milk is heated to 140° F. for twenty minutes, 



