THE CHEMISTRY OF CHEESE MAKING 91 



It would be possible for cheese to be made by allow- 

 ing the milk to sour by natural processes, but under 

 such conditions a poor quality of cheese is produced, 

 for the process of fermentation cannot then be con- 

 trolled as when a starter is used for ripening the 

 milk and rennet for coagulating it. The chief 

 action of rennet in cheese making is to coagulate 

 the milk. In the ripening of the cheese, the rennet 

 appears to act secondary to the enzymes or soluble 

 ferments wliicli are normally present in all milk. 



86. The Rennet Test. — The rennet test is employed 

 in cheese making to determine when the milk is in 

 the right condition for adding the rennet. The 

 rennet test is made in the following way : 5 cc. 

 of rennet extract is diluted and mixed in a flask 

 witli 4o cc. of water, 140 cc. of milk from the 

 \at is placed in a small cup, 5 cc. of the diluted 

 rennet solution added and thoroughly stirred, and 

 the time required for the complete coat^ulation of 

 the milk noted. In making the test, a knife is 

 used to determine when the coagulation is com- 

 pleted. If more than sixty seconds are required 

 for coagulation, the milk is not sufficiently ripened 

 for the addition of the rennet. For ordinary pur- 

 poses of Cheddar cheese making, the milk is suffi- 

 ciently ripened when it coagulates in from 45 to 55 

 seconds. If the milk coagulates in less than 40 

 seconds, it is overripe and requires different manipu- 

 lations for cheese-making purposes. The ripeness 

 of the milk, as shown by the rennet test, materially 



