THE CHEMISTRY OF CHEESE MAKING 



93 



maker, and the process of making adapted to exist- 

 ing conditions. After the rennet has been added and 

 thoroughly mixed, about twenty minutes are allowed 

 for complete coagulation of the milk. The time of 

 coagulation, however, will vary with the conditions 

 stated. When the curd is in a state where it 

 readily "breaks" and maintains its form, it is cut 

 with a curd knife into small cubes. After cutting, 

 the mass is gently agitated for about five minutes so 

 as to secure hardening of the curd particles and to 

 prevent mechanical 

 losses of fat. This 

 agitation also pre- 

 vents the curd from 

 matting and forming 

 large masses. The 

 temperature of the 

 vat is then raised 

 gradually at the rate 

 of two degrees for every five minutes until a tem- 

 perature of 102 F. is reached. The stirring is 

 continued at intervals to prevent the curd parti- 

 cles from matting. The heating of the curd brings 

 about a number of important changes and results in 

 contraction of the curd and more complete expulsion 

 of the whey. The changes brought about by the di- 

 gestive ferments present in the rennet and the milk 

 cause a softening of the curd. The ripeness of the 

 curd in the vat is determined by the hot-iron test. 

 This test is made in the following way : A piece of 



FIG. 17. Cheese vat. 



