150 THE CHEMISTRY OP THE FARM. 



butter made from sour cream, as the latter always 

 contains curd, a substance very prone to change. Salt 

 is generally added to improve the keeping quality of 

 butter. Good churning should result in 96 per cent, of 

 the cream fat being obtained as butter fat. 



First-class butter will contain a minimum of about 

 10 per cent, of water, and 0*5 per cent, of casein. In 

 ordinary fresh butter the water is usually 11 15 per 

 cent., the fat 83 87, the casein 0'6 1*0, the milk sugar 

 0-2 -0-7, and the ash O'l 3'0 per cent. The amount of 

 ash depends chiefly on the quantity of salt added. Of 

 the fatty acids in butter about 6 per cent, are soluble in 

 water when separated from the glycerol with which they 

 are combined ; this fact serves to distinguish butter from 

 other animal fats in which soluble fatty acids are absent. 

 When butter becomes rancid the glycerides of the fatty 

 acids are partly decomposed, and the fatty acids liberated; 

 the odour and flavour of rancid butter are largely due to 

 free butyric acid. 



Buttermilk. The liquid remaining in the churn after 

 the separation of the butter from the cream varies a good 

 deal in composition; the average will be about as follows : 

 Water, 90'1 ; albuminoids, 4'0 ; fat, 1*1 ; sugar, 4'1 ; ash, 

 0*7 per cent. The albuminoid ratio would thus be 

 1:1-6. 



Cheese. This substance is prepared by the action of 

 rennet on milk. Rennet is made by extracting the 

 fourth stomach of the calf with water containing 5 per 

 cent., or more, of common salt. Its power of coagulating 

 milk is due to the presence of a ferment, which doubtless 



