334 THE CHEMISTRY OF DAIRYING 



Changes of a similar kind occur in the ripening of cheese. 

 They are produced by the action of enzymes probably derived 

 from certain types of bacteria. At all events the insoluble 

 coagulum becomes partially resolved into peptones and other 

 soluble proteins, amides, e.g. leucine, tyrosine, etc., and even 

 ammonium compounds. It is these soluble compounds, their 

 total quantity and relative proportions that chiefly determine 

 the flavour and other properties which distinguish the different 

 types of cheese. The strength of the rennet used and the 

 time it is allowed to act probably influence the velocity of 

 these changes to a considerable extent. The original acidity 

 of the milk, the temperature at which it is coagulated, and to 

 which the curd is subsequently exposed, the temperature and 

 humidity of the ripening room, all tend to check the develop- 

 ment of certain types of bacteria and favour that of others. It 

 is by regulating these various conditions, therefore, that the 

 cheesemaker is able to control the action of the organisms, and 

 so produce a preponderance of the particular type of fermen- 

 tation he desires, i.e. to make the different kinds of cheese. 



So far as is known, the fat suffers no change in the process 

 of ripening. The milk sugar is nearly all drained off in the 

 whey. Any that remains is rapidly transformed either into 

 lactic acid or, under certain conditions, into carbon dioxide, 

 hydrogen, alcohol,, and other products. The holes or 

 vacuoles commonly seen in Gruyere, and the smaller pores 

 in other kinds of cheese, are due to the formation of such 

 gaseous products. The lactic acid, derived directly from 

 the milk or formed subsequently in the process of ripening, 

 imparts a certain flavour to the cheese. Lactic acid is, 

 however, capable of undergoing secondary fermentations 

 which result in the formation of butyric acid and other 

 products. 



A certain amount of water is formed in many of these 

 changes, and a certain amount evaporates in the process of 

 ripening. The latter, however, generally exceeds the former, 

 and the cheese, therefore, tends to become drier. 



