14 Testing Milk and Its Products. 



or above the limits given, but the mixed milk from a 

 whole herd rarely falls outside of these limits. The 

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

 is 3 per cent; Rhode Island allows milk containing 2.5 

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

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

 chussetts 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 com- 

 ponents of the milk by the fact that they contain the 

 element nitrogen. Another name is albuminoids or pro- 

 tein 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 temperature of 170 F. 

 being sufficient to effect a perfect coagulation. The 

 casein, with fat and water, form the main components of 

 nearly all kinds of cheese. In the manufacture of ched- 

 dar 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 in some countries is also made into 

 cheese by evaporating the whey with constant stirring; 

 whole milk of cows or goats is often added and incor- 

 porated into such cheese (primost, gjedost). 



Casein is present in milk partly in solution, in the 

 same way as milk sugar, soluble ash -materials and albu- 

 men, and partly in suspension, in an extremely fine col- 

 loidal condition, mixed or combined with insoluble 



