Miscellaneous Feeding Stuffs. 227 



It will be seen that the last milk drawn was from seven to ten 

 times as rich in fat as that first di'awn. On the other hand, the 

 serum, which consists of the milk solids less the fat, is substan- 

 tially constant in composition, 



351. Milk fat. — In the manufacture of butter, the object of the 

 dairyman is to secure all the fat possible from the milk with but a 

 trace of the other constituents. By the use of the centrifugal sep- 

 arator most of the fat is abstracted from the milk, the residue 

 amounting to from one to three-tenths of one per cent. In grav- 

 ity creaming, which was formerly the only process employed, about 

 seven-tenths of one per cent, of fat is usually left in the skim 

 milk. For this reason gravity skim milk is usually somewhat 

 superior for feeding purposes to that skimmed by the centrifugal 

 sejjarator. 



352. The nitrogenous constituents. — As the table shows, aver- 

 age milk contains 3.6 per cent, of nitrogenous substances, mainly 

 casein and albumen, in the proportion of about five parts of casein 

 to one of albumen. 



In the manufacture of cheese^ rennet is added to the milk for 

 the purpose of coagulating the casein. The casein thus coagulated 

 entraps the fat globules and carries most of them into the curd. 

 The albumen, which does not coagulate, together with the milk 

 sugar passes into the whey, as does some of the fat. The amount 

 of fat present in whey varies greatly, according to the manner in 

 which the curd is manipulated previous to drawing the whey. 



353. Milk sugar. — Milk sugar in separate form is a white 

 I)Owder of low sweetening power, and is much less soluble than 

 cane sugar, which it closely resembles in chemical composition. 

 When milk sours some of i lie sugar is changed to lactic acid, which 

 has the effect of coagulating or curdling the casein. When about 

 eight-tenths of one per cent, of acid has developed, fermentation 

 coiises, so that sour milk i^uiy still contain much of the original 

 milk sugar. Judging from its composition, milk sugar has about 

 the sa}ae value for feeding as the same weight of starch. 



354. Ash in milk. — In each hundred pounds of milk there are 

 about seven -tiuths of a pound of mineral matter, consisting chiefly 

 of phosphates and chluiid,s oi potash, soda and lime. 



