Bacteria in Market Milk. 215 



ing milk. Pasteurization remains the only safeguard, 

 and it is probable that within a short time all the larger 

 cities will require the pasteurization of all milk, except 

 that produced under strict supervision. 



As previously mentioned heating causes certain 

 changes in milk. In the treatment of market milk it is 

 desirable to use as low temperatures as will suffice to de- 

 stroy the disease-producing bacteria. It is fortunate 

 that temperatures that will insure this result have little 

 effect on the milk. The temperatures now recommended 

 for pasteurization are as follows : 



158 degrees F. for 3 minutes. 



155 degrees F. for 5 minutes. 



152 degrees F. for 10 minutes. 



148 degrees F. for 15 minutes. 



145 degrees F. for 18 minutes. 



140 degrees F. for 20 minutes. 



In actual practice the milk is heated to 145 degrees 

 for 25 to 30 minutes. The acid-forming bacteria are not 

 completely destroyed and the pasteurized milk as a rule 

 will undergo the same type of fermentation as raw milk. 

 It is, however, deemed essential that all pasteurized 

 milk be sold as such ; that it be delivered to the con- 

 sumer within twenty-four hours after pasteurization 

 and that no milk be pasteurized a second time. 



The continuous pasteurizing machines have the disad- 

 vantage that a small portion of the milk passes through 

 so quickly that all pathogenic bacteria therein might not 

 be destroyed, (p. 131). This has led to the use of the 

 "holding" process in which the milk is heated to the de- 

 sired temperature and then placed in tanks where it re- 

 mains at this temperature for any desired" time. Every 

 portion is thus treated in a uniform manner. 



