FORTY-SECOND ANNUAL CONVENTION 301 



pasteurize all sweet or all sour cream without much trouble, but 

 it is the mixing of sweet and sour cream that causes curdling and 

 excessive losses in the buttermilk, as well as a mealy rondition 

 in the body of the butter. 



The curdling of cream during pasteurization and excessive 

 losses in the buttermilk are the two main difficulties met with, 

 in pasteurizing, and the two usually go hand in hand : when 

 curdling of cream occurs, it always results in excessive losses in 

 rhe buttermilk, and excessive losses in buttermilk seldom occur 

 if proper churning temperatures are used, except when the cream, 

 curdles during pasteurization. 



The curdling or coagulation of mixed sweet and sour cream 

 is due to a combination of the action of the acid in sour cream 

 upon the casein in sweet cream in the presence of heat. The 

 mixing of sweet and sour cream does not alone cause curdling, 

 but when the casein in sweet cream is subjected to the action of 

 the lactic acid in sour cream for a short time, it seems to become 

 sticky, and when a temperature of close to 125 degrees F., is 

 reached, the curdling or coagulation takes place. Thus, it will be 

 seen that the sweet cream curdles and not the sour cream, as 

 many buttermakers seem to believe. 



Remember, it is the combination of the action of the lactic 

 acid on the sweet curd for a short time, together with a temper- 

 ature of 125 degrees, that causes curdling. Either one separ- 

 ately does not cause the curdling; it is the contamination of the 

 two. 



When cream curdles during pasteurization, it always causes 

 an abnormal loss of fat in the buttermilk. This is due to the 

 particles of casein adhering when in a sticky condition, these 

 clusters of casein again enclosing particles of fat which are not 

 liberated during the process of churning. 



The big problem confronting the buttermaker is how to 

 handle his cream so as to pasteurize it without _curdling. We 

 will suggest several methods and then let the buttermaker judge 

 which is most practical under his conditions. The sweet and 

 sour cream may be pasteurized separately if the run is large 

 enough to make this practicable. If this is done, we would 



