224 PRACTICAL DAIRY BACTERIOLOGY 



problems, and partly also to the fact that there are very many 

 different kinds of cheeses, and the ripening of the different 

 types is not by any means due to the same agency. There are 

 no fewer than 250 varieties of cheese in France alone, and, 

 although other countries have hardly as many, the varieties 

 elsewhere are also numerous. These varieties may be fairly 

 well arranged into two groups: (i) the hard cheeses, and (2) 

 the soft cheeses, although there are some intermediate forms.. 

 The ripening of the hard cheeses is very different from that of 

 the soft, and the ripening of the different types of the soft 

 cheeses varies greatly one from the other. Each kind of cheese 

 must, therefore, be studied as a special problem, and while 

 the ripening of some kinds of cheeses has been thoroughly 

 studied and is quite well understood, that of others remains 

 wholly for the future to explain. At the present time, there- 

 fore, we can give only some general statements regarding 

 cheese ripening and its relation to micro-organisms. 



To understand the phenomenon in question we notice, first, 

 that the changes occurring in the ripening can be divided into 

 three classes: (i) physical changes affecting the general ap- 

 pearance of the curd; (2) chemical changes affecting its com- 

 position; (3) chemical changes which develop the cheese flavors. 



Chemical and Physical Changes. These may be considered 

 together, because they are doubtless closely connected. A very 

 noticeable physical change takes place in the texture of the 

 curd. When first made this is hard, rather dry, and somewhat 

 tough and elastic ; but as the ripening occurs its texture changes, 

 its elasticity disappears, and it turns eventually into a softer 

 constituency, which differs very much in the different types of 

 cheeses. The softness of the resulting cheeses is dependent 

 largely upon the amount of moisture it contains and the temper- 

 ature. The larger the amount of moisture left in the cheeses, 

 other things being equal, the softer it will become; and the 

 higher the temperature at which the cheese is kept, the softer 



