CURD-MAKING 57 



the color should be added after the starter and just before 

 the addition of the rennet. The amount is determined 

 by the color desired in the cheese. The usual amount 

 varies from one to four ounces to each thousand pounds 

 of milk. Before adding, the color should be diluted in 

 either milk or water, preferably water. It should then 

 be mixed thoroughly with the milk. 



79. The acidity factor. Milk as drawn shows a meas- 

 urable acidity when titrated to phenolphthalein with 

 normal sodium hydroxide. This figure varies with the 

 composition of milk. Casein itself gives a weakly acid 

 reaction with this indicator. Calculated as lactic acid, 

 this initial acidity varies within fairly wide limits, records 

 being found from 0.12 to 0.21 of one per cent or even more 

 widely apart. Commonly, however, such titration shows 

 0.14 to 0.17 per cent. Some forms of cheese (Limburger, 

 Swiss, Brie) are made from absolutely fresh milk. Acidity 

 from bacterial activity is important as a factor in the 

 making of most types of cheese and probably in the 

 ripening of all types. 



Increasing the acidity of the milk hastens rennet action 

 and within limits produces increased firmness of the curd. 

 If carried too high, acidity causes a grainy or sandy curd. 

 Normally fresh milk is sufficiently acid in reaction when 

 tested to phenolphthalein to permit rennet to act, but 

 the rate of action increases rapidly with the develop- 

 ment of acid. Increase of acidity may be accomplished : 

 (a) by the addition of acid as has been done by Sam- 

 mis l and Bruhn in pasteurized milk for Cheddar 

 cheese; or (6) by the development of acid through the 



1 Sammis, J. L., and A. T. Bruhn, The manufacture of cheese 

 of the Cheddar type from pasteurized milk, U. S. Dept. Agr. 

 Bur. An. Ind. Bui. 165, pages 1-95, 1913. 



