Composition of Milk and Its Products. 13 



Cow's milk generally contains between three and six 

 per cent, of fat; in American milk we find, on the 

 average, toward four per cent, of fat. The milk from 

 single cows in perfect health will occasionally go below 

 or above the limits given, but mixed herd milk rarely 

 falls outside of these limits. The standard adopted by 

 the U. S. government for fat in milk is 3.25 per ct. 

 The legal standard for fat in milk in most states of the 

 Union is 3 per cent. ; Rhode Island allows milk contain- 

 ing 2.5 per cent, of fat to be sold as pure, while Georgia 

 and Minnesota require it to contain 3.5 per cent., and 

 Massachusetts 3.7 per cent, (in the months of May and 

 June; see Appendix, Table II). 



18. Casein and albumen. These belong to the so- 

 called nitrogenous substances, distinguished from the 

 other components of the milk by the fact that they con- 

 tain the element nitrogen. Another name is albumin- 

 oids or protein compounds. Casein is precipitated by 

 rennet in the presence of soluble calcium salts, and by 

 dilute acids and certain chemicals ; albumen is not acted 

 upon by these agents, but is coagulated by heat, a tem- 

 perature of 170 F. being sufficient to effect a perfect 

 coagulation. The casein, fat, and water, are the main 

 components of nearly all kinds of cheese. In the manu- 

 facture of cheddar and most other solid cheeses, the 

 casein is coagulated by rennet, and the curd thus 

 formed holds fat and whey mechanically, the latter 

 containing in solution small quantities of non-fatty 

 milk solids. The albumen goes into the whey and is 

 lost for cheese making in some countries it is also made 

 into cheese by evaporating the whey under constant 



