BACTERIA IN CHEESE 233 



the well-ripened cheeses hardly any bacteria, except lactic acid 

 organisms, are present, and this class of bacteria does not, so 

 far as is known, have any power of producing cheese flavors. 

 Some bacteria, if they grow in proper abundance in milk, will 

 in time develop well known cheese flavors ; but these organisms 

 have not been found in old, strongly flavored cheeses. Whether 

 they have anything to do with the production of cheese flavors 

 is therefore uncertain. It has been suggested by Rogers l that 

 the flavor of cheeses is due to the bacteria which grow in them 

 during the first few days. Liquefying bacteria are found during 

 this early period, and before the miscellaneous bacteria disap- 

 pear, as they do later, some of these liquefiers may secrete from 

 their bodies substances, possibly enzymes, that continue their 

 action in the cheese slowly, but for a long time. Although the 

 bacteria that produce them soon die, the chemical ferments 

 which they have produced continue their activity until they 

 finally produce the new products that give the flavor. On the 

 other hand, Harrison and Connell a think the lactic bacteria 

 most closely associated with flavor. All of this, however, is at 

 present largely theoretical. We know that the digestion of the 

 casein, whether produced by pepsin or by galactose, does not 

 produce the cheese flavors. We know that certain kinds of 

 bacteria are capable of producing these flavors, and while the 

 matter has not yet been settled, the probability seems to be that 

 the flavoring of the cheese must be attributed to bacterial action. 

 Other Functions of Bacteria in Cheese-ripening. Whether or 

 not bacteria are the source of the flavor of hard cheeses, there 

 is no doubt that they do play a very important part in cheese- 

 making in several distinct directions. As has already been 

 indicated, the first step in the ripening of the cheese is the 

 souring of the curd, and this is produced by lactic acid bacteria. 

 It seems to be quite necessary that this should take place in 



1 Rogers. Bui. 62, Bu. An. Ind., 1905. 



2 Harrison and Connell. Cent. f. Bact., II., xi., p. 637, 1904. 



