30 SCIENCE AND PRACTICE OF CHEESE-MAKING 



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enough, but this can be varied from 96° F. in the 

 springtime to 102° F. in the fall. Curd from milk 

 rich in fat is harder to firm than curd from poor 

 milk, owing generally to the smalle r proportion 

 of casein relative to fat. Thus, milk containing 

 3 to 3.6 per cent of fat ordinarily behaves at 94° to 

 96° F. the same as milk with 4 to 5 per cent of fat 

 does at 98° to 102° F. In extreme cases, the 

 temperature may have to be raised even higher to 

 firm successfully the curd from overripe milk. High 

 heating generally causes a corky or rubberv-bodied 

 cheese. 



How to regulate heat. — Care must always be 

 taken not to raise the temperature of the curd too 

 rapidly. Usually the temperature can be raised 

 about 2° F. in every 5 minutes, but when the lactic 

 acid formation is slow, 1° F. every 5 minutes may 

 be sufficient. The following rule is a reliable guide 

 in heating: 



Rule for heating. — If, after cutting, the whey 

 around the curd shows 0.12 per cent acidity, allow 

 60 minutes for heating; 0.13 per cent acidity, al- 

 low 40 minutes for heating; 0.14 per cent acidity, 

 allow 30 minutes for heating; 0.145 per cent acidity, 

 allow 25 minutes for heating; 0.15 per cent acidity, 

 allow 20 minutes for heating. 



It is noticeable that the whey at this stage con- 

 tains 0.05 to 0.08 per cent less of acidity than the 

 milk does when the rennet is added. This is due 

 to the fact that the whey contains no casein and the 

 casein in the milk has the power of acting like an 

 acid in neutralizing alkali. 



