COMPOSITION AND PROPERTIES OF BUTTER 547 



constituted a little over 60 per cent of the protein, or curd, in 

 butter, while the remainder of about 40 per cent is casein. 



Storch's findings and conclusions may assist in the explana- 

 tion why, even when the churning process is stopped while the 

 butter granules are still exceedingly minute, and when this 

 butter is subsequently very thoroughly washed with repeated 

 washings, so that the butter drains perfectly clear, it is not 

 possible to reduce the curd content, as determined by the Kjel- 

 dahl method, to any appreciable extent below about .4 per cent. 

 This slimy protein substance does not wash out. 



The curd content of butter is determined and expressed in 

 one or the other of two entirely different ways and yielding 

 results in per cent curd, that differ from one another. One way 

 is to determine the nitrogen content of butter, and by multiply- 

 ing the results by the factor 6.38, expressing it as per cent 

 protein. This represents the true curd content. The other way 

 is to determine the per cent curd by difference, by deducting 

 the sum of the per cent of fat, moisture and salt from 100. In 

 this case the per cent curd so obtained embraces, aside from the 

 protein, also the traces of ash, acid and lactose contained in 

 butter. This is termed the physiological curd. 



In the case of the true curd of butter, the percentage of 

 curd usually fluctuates between about .5 per cent and one per 

 cent, averaging about from .6 to .7 per cent, provided that the 

 butter is washed in a normal manner. 



Butter made from sweet cream, and unsalted butter, has 

 a slightly higher curd content than butter made from ripened 

 cream and butter that was salted. Butter that is only very 

 slightly washed contains more curd than butter in the manu- 

 facture of which the churn is stopped when the granules are 

 still very small and which are washed thoroughly. Butter that 

 is not washed at all usually contains from about 1 to 1.5 per 

 cent curd. 



In case of expressing the curd content as physiological curd, 

 the percentage of curd averages from .5 to .6 per cent higher than 

 the true curd. 



The Salt. The salt is the one constituent of butter strictly 

 foreign to the natural composition of butter, unsalted butter con- 



