Relation of Bacteria to Butter. 69 



The next step in the history of butter making, a step 

 toward better control of the flavor of the product, was to 

 heat the cream to kill the acid bacteria already present 

 and thus, to give a free field to the bacteria in the starter. 

 The pasteurization of cream is a most successful process. 

 All the butter made in Denmark is from pasteurized 

 cream; much of the butter made by large creameries in 

 this country is also treated in the same way. It repre- 

 sents the highest type of modern butter making. The 

 cream is pasteurized in ''continuous flow" machines in 

 which it is heated momentarily to 170-190 F., and 

 cooled at once. Before churning the cream must be 

 cooled to 50 F. and kept at this temperature for some 

 hours, otherwise the butter is apt to have a soft and 

 mushy texture. 



Ripened cream churns more easily than does sweet 

 cream and the loss of butter fat in the butter-milk is not 

 so great. This is of considerable importance in cream- 

 eries where the daily output is several thousands of 

 pounds. 



Details of cream ripening. The cream should be 

 from clean milk and allowed to sour at about 70-80 F. 

 Pure-culture starters have not been extensively used on 

 the farm, but undoubtedly they would be of great value. 

 They can be propagated in small vessels as fruit jars, 

 milk bottles, etc. The details that must be observed in 

 the propagation need not be given here as full instruc- 

 tions accompany each pure culture sent out by the manu- 

 facturers. 



The cream should be allowed to sour until the acidity 

 is from 0.5-.65 per cent. If the acidity is lower, the 

 flavor of the butter will be very mild. If the acidity 

 increases to 1 per cent, the flavor is apt to be undesirable. 



