3IO SCIENCE AND PRACTICE OF CHEESE-MAKING 



(b) The character of the coagulation is af- 

 fected by the temperature at which the rennet- 

 enzym acts. Thus, at 60 F., the curd is flocculent, 

 spongy and soft; at 77 to 113 F., it is more or less 

 firm and solid; at 122 and above, it is very soft, loose 

 and inclined to be gelatinous. 



(c) Milk heated above 150 F. for a consider- 

 able length of time coagulates less rapidly than nor- 

 mal milk. The coagulum of such heated milk is 

 highly floeculent, never a firm and solid mass, in the 

 absence of soluble calcium salts or acids. Boiled 

 milk fails to coagulate normally, if at all, by rennet- 

 enzym, unless treated with some soluble calcium salt 

 or some acid. The degree of heat used decreases the 

 amount of soluble calcium salts in milk and also drives 

 out any carbon dioxid present. 



(7) Exposure to sunlight weakens the coagulating 

 power of rennet-extract. 



(8) Solutions of rennet-extract are affected b\ 

 heat. Rennet-extract heated for some time above 

 140 F. becomes permanently weaker, or inactive. 

 Rennet-enzym begins to suffer injury at about 120 F. 

 Weak solutions are injuriously affected at tempera- 

 tures as low as 105 F. Strong solutions are weak- 

 ened by heating at 150 F. for 15 minutes, but are not 

 entirely destroyed. High temperatures destroy the 

 activity of rennet-enzym gradually, not instantane- 

 ously. 



(9) Increase in amount of rennet-extract or in 

 strength of rennet-enzym hastens coagulating effect on 

 milk. 



(10) Milk, freshly draivn, curdles more com- 

 pletely than when allowed to cool, due to lowering of 

 temperature and, perhaps, to the presence of more 



