288 Agricultural Chemistry. 



among which are "plasmon" and "nutrose. " "Plasmon" is 

 made by treating the curd of skimmed milk with sodium bi- 

 carbonate and drying the thoroughly mixed product in an at- 

 mosphere of carbon-dioxide. "Nutrose" is also a sodium com- 

 pound of casein. 



Cheese. The principal varieties of commercial cheese are pre- 

 pared from milk by the action of rennet. Rennet is made by 

 extracting the fourth stomach of the calf with a 5 to 10 per cent 

 solution of common salt. Its power to coagulate milk is due to 

 the presence of an enzyme called rennin, which plays a similar 

 part in the process of digesting milk in the calf 's stomach. Ren- 

 nin coagulates the casein of the milk, forming a curd which 

 mechanically entangles almost all the fat of the milk, leaving 

 the albumin and sugar in the whey. Rennin acts more rapidly 

 at about 102 to 104 F. In cold milk it is slow in its action, 

 while at temperatures above 120 F. it is retarded, its action en- 

 tirely ceasing at 130 F. In milk containing some acid, but not 

 enough to curdle it, rennin action is hastened. 



It is impossible in a work of this scope to describe the varieties 

 of cheese and their methods of manufacture. 



The common practice followed in the preparation of American 

 cheddar cheese is to "ripen" the milk to an acidity correspond- 

 ing to about 0.25 per cent of lactic acid. This is done by adding 

 to it a starter consisting of sour milk or a pure culture of lactic 

 organisms. The necessary rennet is then added, the milk being 

 previously warmed to 82 to 85 F. After the curd is sufficiently 

 firm, requiring about 30 minutes, it is cut into cubes and the 

 temperature of the vat raised to 100 F. It is maintained at 

 that temperature for 1 to 2 hours, during which time the curd 

 shrinks and the acidity increases. After proper acidity is de- 

 veloped, the whey is drawn, the curd piled in one end of the vat 

 and kept warm. In this condition it mats into a solid mass. It 

 is finally passed through a grinding mill, salted, and pressed into 

 molds. The cheese is then placed in a curing room at a tem- 

 perature of 50 to 60 F. and allowed to ripen. A lower tern- 



