148 THE CHEMISTRY OP THE FARM. 



of milk, are always present in small quantity. In sweet 

 cream the casein may be about one-tenth of the fat ; in 

 the cream from milk which has soured during setting the 

 casein forms a much larger proportion. 



The perfectly sweet cream obtained by using ice, or the 

 centrifugal separator, is frequently slightly soured or 

 "ripened" before churning. For this purpose a little 

 buttermilk is stirred in, and the cream warmed to about 

 70. As soon as the cream thickens it must be churned, 

 or else immediately cooled, to prevent the change proceed- 

 ing further. It is claimed that rather more butter can 

 be obtained from ripened cream than from sweet cream ; 

 the flavour of the butter also is altered. 



Skim Milk. Milk thoroughly skimmed in the ordinary 

 way will still contain about 0.8 per cent, of fat, and more 

 thao this quantity is frequently present. When ice has 

 been used, the percentage of fat left in the milk will be 

 05 to 0*7; and when the centrifugal machine has been 

 employed, 0*2 to 0*5. Skim milk obtained in the ordinary 

 way will contain about as follows : water, 90'0 ; albu- 

 minoids, 3'6; fat, 0*8; sugar, 4*9; ash, 0*7. Its specific 

 gravity is generally 1*034 to 1'037. Skim milk is a very 

 nitrogenous food, the albuminoid ratio being as high as 

 1 : 1-8. 



Butter. The object of butter-making is to bring 

 about the union of the fat globules which in milk and 

 cream have existed separate from each other. The skilled 

 butter-maker is not, however, satisfied with producing 

 a solid mass of butter-fat ; for butter to be of good quality 

 it must possess a certain texture and grain, and be neither 



