In the laboratory the ferment is extracted by chemicals and a pure, clear liquid extract is prepared, of uniform strength and good keeping quality. Or the extract is condensed into a powder which again is compressed into tablets of great strength.
The ferment acts best when the milk is lukewarm, but it will do the work at temperatures ranging from 50°, or even lower, to 120° F. Strongly pasteurized or sterilized milk will not curdle with rennet, but milk pasteurized at a low temperature is not changed enough to prevent it from making a firm curd. More rennet does not make a firmer curd but causes the milk to curdle quicker; less rennet makes the process slower. Diluted milk will not curdle firmly, and the failure of milk to make a smooth coagulum of the usual consistency and in the usual time, the temperature being right and the regular amount of a standard rennet being used, is a never-failing proof that something is the matter with the milk. It has been changed from its natural condition by over-heating in pasteurization or by watering or doctoring, or it has not been properly ripened.
[9]. W. O. Atwater, Farmers’ Bulletin No. 142.
[10]. Dr. E. V. McCollum in “Hoard’s Dairyman.”
[11]. Prepared for “The Story of Milk” by A. Louise Andrea.
BIBLIOGRAPHY
Cheese Making; John W. Decker, Columbus, O.
The Milk Question; M. J. Rosenau, Houghton-Mifflin Co., Boston.
The Manufacture of Cheese of the Cheddar Type from Pasteurized Milk; J. L. Sammis and A. T. Bruhn, Bulletin 165, Bureau of Animal Industry, Washington, D. C.