234 THE OHEMISTEY OF THE FARM 



Bipening. — 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 proceeding further. It is claimed 

 that rather more butter can be obtained from ripened 

 cream than from sweet cream; this is especially the 

 case when the cream is thin. The flavour of the 

 butter also is altered, and to popular taste improved, 

 by ripening the cream. The change is due to the 

 action of micro-organisms, and the thickening is 

 probably brought about by the curdling of the casein. 



SMm and Separated Milk.— Milk thoroughly skimmed 

 after shallow setting will still contain about 0*8 per 

 cent, of fat, and more than this quantity is frequently 

 present. With deep setting and ice the percentage 

 of fat left in the milk will be O'S— O'T. When the 

 centrifugal machine has been employed the percentage 

 will be 0*05 — 0*3. In the experiments at Geneva, 

 U.S., it was found that, with deep setting, twice as 

 much fat remained in the skim milk from Holstein 

 cows as in that of Guernseys and Jerseys, owing 

 to the slower rising of the small fat globules in 

 Holstein milk. With the centrifugal separator the 

 results are very similar whatever the source of the 

 milk ; the size of the globules has in this case little 

 influence. 



Skim milk obtained by shallow setting will contain 

 in 100 parts about as follows : Water, 90*0 ; albu- 

 minoids, 3*6; fat, 0.8; sugar, 4*9; ash, 0'7. Its 



