560 MANUAL OF MILK PRODUCTS 



use of cold water or a blast of cold air. Theoretically, this 

 method is preferable to that in which the milk is handled after 

 it has been pasteurized, since it prevents all possible chance for 

 recontamination. It is a newer method and not in general 

 use, but will doubtless become more common as soon as satis- 

 factory machinery can be developed for handling milk on a 

 large scale. 



Another phase of this general question which is of great im- 

 portance to the dairyman is the protection of his herd against 

 the spread of tuberculosis. This disease may be transmitted 

 directly from one animal to another, or it may be carried 

 through an infected milk supply, usually in the form of skimmed 

 milk, buttermilk, or whey which the farmer brings back from 

 the factory. 



Pasteurization of skim-milk and whey (Farrington) 1 



It has been demonstrated that bovine tuberculosis may be 

 carried from one herd of dairy cows to another by means of 

 creamery skim-milk, and that a temperature of 176 F. kills 

 the tuberculosis germs. The method of heating milk to a tem- 

 perature at which disease germs will be destroyed is called 

 pasteurization. In view of these facts, the pasteurization of 

 skim-milk as well as buttermilk and whey becomes a matter of 

 vital importance to the dairyman. 



Four methods of pasteurizing skim-milk at creameries have 

 been suggested : 



First, by using exhaust steam from the creamery engine. 



Second, by forcing steam directly from the boiler (high- 

 pressure steam) into the skim-milk. 



Third, by passing the skim-milk over a heated metal surface, 

 as is common in the various whole-milk and cream pasteurizers 

 now on the market. 



i Wis. Bui. 148. 



