70 CHEESE AND CHEESE-MAKING 



TESTING FOR ACIDITY. There are two 

 methods by which to determine the ripeness 

 or amount of acidity developed (a) By means 

 of rennet. Take 4 oz. of milk at the temperature 

 at which it is intended to rennet the milk, and 

 add i drachm of rennet ; if the milk coagulates 

 in 20 to 22 seconds it is ready for renneting. 

 (b) By means of chemical re-agents. Take out 

 10 c.cs. of milk with a pipette, run into a white 

 porcelain dish, and add three drops of phenol- 

 phthalein solution (addition of an alkali to a 

 solution of phenol-phthalein produces a pink 

 coloration). From a burette allow to drop 

 soda solution of such strength that i c.c. of it 

 will neutralize O'Oi gramme of lactic acid. 

 Whilst adding the soda solution, keep constantly 

 stirring the milk in the dish, and on the appear- 

 ance of the faintest tinge of pink which remains 

 permanent, you know that the whole of the 

 lactic acid in the milk is neutralized. If it 

 requires 2 c.cs. of the soda solution for this 

 purpose, we know that we have O'2 per cent, of 

 acid in the milk, which is about the correct 

 amount for making Cheddar. The former of 

 these methods is probably to be preferred, 



