368 PHYSIOLOGICAL CHEMISTRY. 



obtained from it by mechanical processes after it has been 

 changed as described above : 



Butter, 3.5 parts. 



I 

 > 



Skimmed milk. 80 



) Butter, 3.5 



Cream, 20 [ .,, , _ 



j Buttermilk, 16.5 



) Curd, 8.0 



} Whey, 72.0 



Butter. Even in the thickest varieties of cream there is no 

 cohesion between the fat globules, whilst in butter the fat has 

 actually cohered. This change is accomplished by violently 

 agitating (churning) the cream, when the fat particles gradually 

 combine with each other, whilst the liquid (buttermilk) sepa- 

 rates. 



Chemically, butter is milk-fat, a mixture of different fats or 

 glycerides of the fatty acids, chiefly palmitic and butyroleic 

 acid, with butyric, capronic, and caprylic, and occasionally 

 stearic acid; it always contains a certain proportion, 15 to 16 

 per cent., of water, besides traces of casein, salts, coloring 

 matter, etc. 



For curing butter, common salt is often used ; the quantity 

 added should not exceed 5 per cent. 



The composition of buttermilk has been given above ; when 

 freshly obtained from sweet cream it is a pleasant drink and a 

 wholesome food. 



Cheese consists mainly of casein, milk-fat, water, and inorganic 

 salts ; these constituents vary as follows : 



Water, 61 to 28 parts. 



Casein, 15 to 35 " 



Fat, 20 to 30 " 

 Salts, 4 to 7 " 



Cheese is made either from pure milk, from skimmed milk, 

 or from a mixture of milk and cream, and accordingly varies 

 highly in composition. Practically, cheese is made by causing 

 milk to coagulate (either by allowing it to stand or by the addi- 

 tion of rennet, acids, or other substances), and separating the 

 curd (casein and fat) from the whey by mechanical means, such 

 as filtering arid pressing. The curd is placed in suitable moulds 

 and afterwards allowed to stand or " ripen " for a shorter or 



