3C0 THE dairyma:n^*s manual. 



action is explained by the fact tliat tlie active principle of 

 the rennet is dissolved in the ^vater which is intimately 

 diffused though the whole mass of the milk and an 

 infinite number of centers of action are produced in con- 

 tact with every particle of the caseine. Acid is thus 

 formed all through the milk ; the soda is neutralized all 

 through it, and the caseine is precipitated very rapidly. 

 But by ordinary souring the caseine is first precipi- 

 tated by the action of the air ; this action is diffused 

 very slowly through the milk, chiefly from the sur- 

 face, and the curdling is therefore effected very slowly. 

 Moreover, this action of the rennet explains why the 

 curd is solidified and the whey remains sweet ; because 

 the acid is neutralized as soon as it is formed, by its 

 combination with the soda of the milk, and the caseine 

 becomes insoluble as soon as the alkali has been com- 

 pletely neutralized by the acid; the acid is then, of course, 

 neutralized by the mutual action of itself and the soda. 

 Thus the milk becomes a neutral or sweet liquid, while 

 the caseine is precipitated as an insoluble curd. If soda 

 could be added again to the whey the curd might be 

 redissolved. 



As soon as the curd is set, a further change immedi- 

 ately becomes imminent. This is the acidification of the 

 whey by the continued decomposition of the remaining 

 milk-sugar, and as the caseine contains about forty per 

 cent of whey this change necessarily affects the curd. 

 It has considerable influence upon the quality of the 

 cheese and is watched very closely by the dairyman. 

 This change is called the ripening of the curd and of the 

 cheese, and is due to the internal decomposition of the 

 curd, and of the cheese which the curd becomes by its 

 continuance. The whey remaining in the cheese contains 

 lactic acid, and as some of this is necessarily left, there is 

 a leaven of fermentation remaining, which is the basis 

 for a continuous decomposition, the end of wliicli would 



