254 AGRICULTURAL BACTERIOLOGY. 



strictly to the shape of the mould. The cheese thus formed 

 is removed from the mould and set in the ripening room, where 

 it is allowed to remain at a constant temperature until the ripen- 

 ing is completed. The ripening takes place slowly, several 

 weeks, and sometimes several months, being required before 

 it is in proper condition for the market. These cheeses are fre- 

 quently made in very large sizes, three or four feet in diameter. 

 They will keep a long time after the ripening is completed. 

 They can be readily exported and carried to all parts of the 

 world, and form the chief cheeses of commerce. 



In the making of both types the ripening is the essential 

 feature. The changes which occur in the cheese during the 

 ripening are by no means thoroughly understood. They may 

 be best considered under two heads, (i) Chemical changes, 

 affecting the solubility of the product. (2) Changes producing 

 the flavor of the cheese. 



I. CHANGES AFFECTING THE SOLUBILITY OF CASEIN. 



Although the chemical changes in the ripening cheese affect 

 all of its ingredients in a measure, the most essential feature is 

 a modification of the casein. Freshly precipitated casein is 

 insoluble in water and, especially after heating, is a hard mass 

 very difficult of digestion. During the ripening of the cheese it 

 becomes converted, to a large extent, into soluble bodies which 

 are much more easily digested and assimilated. As a result, 

 the cheese becomes softer and far more readily handled by the 

 digestive processes of the stomach. This change in the casein 

 is the chief chemical phenomenon in the cheese-ripening. 



In the production of this change in the casein there seem to 

 be two processes at work which have different relations in the 

 different types of cheeses. Since the modern study of bacteri- 

 ology began, it has been assumed that the ripening of the 

 cheese is a process of bacterial growth. It is known that 

 bacteria multiply in cheese and it is also known that certain 



