226 BACTERIA IN CHEESE MAKING. 



aseptic conditions and containing only a small number of 

 bacteria. Cheeses made from such milk, if they are pro- 

 tected in the whole process of manipulation from the pos- 

 sibility of becoming contaminated with bacteria, will not 

 ripen (268). If, however, the milk in question is inocu- 

 lated with certain species of lactic bacteria, all other condi- 

 tions being the same, the cheese ripens normally. These facts 

 show that the ripening of cheese is a double process involv- 

 ing the action of the milk enzymes and also the growth of 

 microorganisms. 



Agency of Microorganisms. The relation of microorgan- 

 isms to the process of cheese ripening is a subject of immense 

 difficulty. The problems have proved to be complicated and 

 their complete solution will require many more years of 

 study. There are several reasons for this. The ripening is 

 a long process. During the whole of this period the bac- 

 teria are growing, and there is a considerable change in the 

 type of bacteria present. Fresh cheese contains quite differ- 

 ent types of bacteria from those that are found in an older 

 cheese. This change in species is quite similar to that already 

 seen in butter, but it complicates the problem and makes it 

 quite difficult to determine to what extent any one species 

 found may contribute to the process of the cheese ripening. 

 Secondly, the cheeses which are manufactured in different 

 localities are widely different from each other. The immense 

 variety of cheeses, each with its own character and each with 

 its own flavor, makes it difficult to answer any question as to 

 cheese ripening in general, for each type of cheese is a prob- 

 lem by itself. One experimenter, working with one variety 

 of cheese, will reach a result quite different from that which 

 another experimenter obtains, working with different 

 che'eses. Some kinds of cheese may be ripened more by the 

 enzyme action; others more by the growth of microorgan- 

 isms. Different students naturally work upon the type of 

 cheeses that are most common in their own locality, and the 



