XV. 



MILK AND MILK PEODUCTS 



339 



Butter=milk resembles skim-milk in composition, but has a 

 peculiar flavour of its own and is generally acid. Its fat content 

 varies considerably and is usually less with ripened than with fresh 

 cream. The fat also varies according to the efficiency with which the 

 churning has been performed. 



Its composition will probably be between the limits 



Water 

 Fat 



Sugar . 



Proteids 



Ash 



Per cent. 

 89-0 to 91-0 

 0-3 3-5 

 4-0 5-0 

 3-3 4-0 

 0-7 0-8 



The losses of fat in butter-making occur in the skimmed milk, in 

 the butter- milk, and in mechanical loss of butter. In American 

 stations, the loss varied from 7 to 25 per cent. When the separator 

 was not used, the loss was greatest with Ayrshire and Holstein cows 

 and least with Guernseys and Jerseys. 



Cheese is formed from milk by coagulating the casein, which en- 

 tangles and carries down with it the greater portion of the fat, while 

 the sugar, albumin and a portion of the casein remain in the whey. 



The coagulation of the casein may be brought about, as already 

 described, either by acids or, more usually and with a better product, 

 by rennet. The curd, after separation from the whey, is pressed and 

 allowed to "ripen," a process somewhat obscure, but probably de- 

 pendent upon micro-organisms. 



The composition of both curd and whey will naturally vary with 

 that of the milk from which they are formed, whether this be whole 

 milk, skim-milk, or milk enriched by the addition of cream. 



The curd and whey from whole milk have the following average 

 composition : 



The character of the curd produced depends largely upon the tem- 

 perature at which the rennet is introduced, also upon the acidity of 

 the milk. 



As already stated, rennet acts most rapidly at about 37 (or 40 

 according to Fleischmann), and if the milk be about this temperature, 

 the curd is firm and hard, while milk at low temperatures or at about 

 50, yields soft curd. The more acid the milk, the more rapid is the 

 action of rennet. 



