XIV.] CHEESE-MAKING 285 



separating from the serum. It is necessary to begin 

 with a certain degree of acidity in the milk. This is 

 obtained by leaving the vats to stand at a proper 

 temperature, stirring from time to time, both to 

 introduce air and to keep the cream mixed with the 

 milk. When the proper acidity has been attained — and 

 this will vary with each kind of cheese, and must be 

 determined by chemical means before the cheese- 

 making is embarked upon — the milk is then brought 

 to a particular temperature and mixed with a certain 

 quantity of rennet. Speaking generally, the more acid 

 the milk, the higher the temperature at which the 

 rennet is added ; and the more rennet is added, the more 

 quickly will the curd come and the firmer consistency 

 will it attain. The necessary degrees of acidity, the 

 most desirable temperature, and the proper strength of 

 the rennet have been worked out for most of the cheeses 

 made on a large scale. When the curd has formed the 

 vat is left to stand until the curd begins to separate from 

 the serum or whey. The curd consists of the casein, in 

 which are entangled the globules of fat contained in the 

 original milk ; the whey contains the albumen of the 

 original milk, all the lactose, and a certain proportion of 

 the salts, some of the calcium phosphate being retained 

 in the casein in the curd. The next stage in cheese- 

 making consists in getting up a suitable consistency in 

 the curd. In the case of a hard cheese like Cheddar, 

 the curd is allowed to contract or shrink in the whey. 

 It is then cut up to facilitate the removal of whey, and 

 the whole mass is raised in temperature to increase still 

 further the consistency of the curd and expel the whey. 

 Finally the curd is lifted out, allowed to drain, and put 

 through the mill in order to reduce it to small pieces. 

 During all these processes the lactic acid bacteria are 

 actively at work, and the curd becomes more and more 



