388 PROPERTIES AND COMPOSITION OF MILK, BUTTER, &C. 



three weeks without throwing up any noticeable amount of 

 cream. 



Cream contains the greater part of the fatty matter of the 

 milk, a small portion of the curd, and considerable water. 



Good cream, when skilfully churned, will yield about 

 one-fourth of its. weight of butter. 



The temperature at which milk can be churned most eco- 

 nomically is 65 Fahrenheit. 



The temperature at which cream can be churned most 

 economically is at 58 Fahrenheit. 



Butter contains more or less of all the ingredients of the 

 milk. Essentially it consists of the fat of milk mixed with 

 about one-eighth of its weight of water, a small quantity 

 of casein or curd (cheesy matter), and of saline matter. 

 The casein seldom exceeds two per cent, of the whole 

 weight. 



The fat of butter, when solidified by pressing out the oil, 

 is identical with the solid fat of the human body. 



The oil of butter is a peculiar kind of fat not hitherto 

 detected in any other substance. 



These two ingredients vary considerably with different 

 samples ; hence the different degrees of hardness which dif- 

 ferent samples present. The solid fat abounds more in 

 winter ; the liquid fat more in summer. They are in about 

 the following proportions in 100 parts : 



Summer. Winter. 



Solid fat 40 65 



Oil of butter... 60 35 



