BACTERIA IN MILK. 



But at present, and for some time past, there has been a tend- 

 ency to recommend a different method of treatment, which 

 is theoretically far less satisfactory, but which practically 

 proves more useful. This method is called pasteurization. 



PASTEURIZATION. 



This treatment, originally devised by Pasteur for the treat- 

 ment of wine, consists in heating the milk to a much lower 

 temperature than boiling and then cooling rapidly. The tem- 

 perature used has varied considerably, from 140 F. to 180 F. 

 In choosing a temperature two factors have been taken into 

 consideration. 



1. It is desired in this treatment to use a temperature which 

 produces the minimum change in the chemical character of 

 the milk and consequently does not give the taste of boiled 

 milk. This has led to the endeavor to find the highest tem- 

 perature to which milk can be subjected without acquiring 

 these tastes. This temperature has been found to be not 

 higher than 1 56 F. 



2. It is desired to use a temperature which will destroy 

 most of the bacteria in the milk. That such temperatures 

 will not destroy all the bacteria is evident enough. But we 

 must remember that the two chief objects to be accomplished 

 are the increasing of the keeping quality of the milk and the 

 removing of danger from disease bacteria. Will these low 

 temperatures produce these two desired results ? 



Such moderate temperatures certainly do increase the keep- 

 ing quality of the milk. While a temperature of 156 F. 

 does not destroy spores, it does very largely destroy the ac- 

 tive, non-spore-bearing bacteria. Now, as we have seen, the 

 lactic bacteria, which are the chief causes of trouble in milk, 

 contain no spores and they are consequently very largely 

 killed by such moderate heat. Hence the total number of 

 bacteria in the milk is immensely reduced and the milk has its 



