278 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



conditions of the dairy remain constant, a constant product 

 may be obtained, without the necessary use of pure cultures. 

 This constancy of conditions depends, however, on locahty. 

 Cheese making, e.g., is carried on in the high Alps imder 

 exceptionally favourable conditions in this respect ; the air 

 is pure, the fodder of the animals consists mainly of grass and 

 hay, from fields to which they themselves contribute the only 

 manure. In the lower Alps, on the other hand, the fodder, 

 and consequently the manure, is subject to variation ; the 

 bacterial atmosphere, therefore, may change from time to 

 time, and the variable conditions manifest themselves in the 

 dairy. 



The chemical changes taking place in ripening cheese 

 consist : — 



{a) In the breaking down of albumin ; 



(b) The sphtting of fats ; 



(c) The fermentation of sugar. 



That these changes are brought about by hving organisms 

 is clear from the fact that, if the curd is treated with an 

 antiseptic, no ripening takes place. Numerous disintegration 

 products of albumin have been detected in ripe cheese, such 

 as leucin, tyrosin, and even ammonia. The splitting up of 

 the glycerides is carried to a further extent than in the souring 

 of cream ; and the activity of the lactic organism is shown, 

 in many cases, in the production of gas, which causes the 

 pitting, so noticeable, e.g., in Gruyere cheese. 



The control of cheese ripening by pure cultures is not so 

 easily carried out as in the case of cr3am, since Pasteurised 

 milk wiU not curdle with rennet. By initial care in the 

 production of the milk and its maintenance at a low tempera- 

 ture, a reasonably puri curd can, however, be obtained. 



The particular organism used as a starter will, of course 

 depend on the character of cheese to be produced ; thus in the 

 case of Eoquefort cheese the mould PenicilUum glaucum is 

 used, whereas in the production of Cheddar cheese, lactic 



