HARD CHEESES. 237 



moreover, it is quite certain that the enzymes play a part of 

 considerable importance, probably a greater part than they do 

 in the ripening of the soft cheeses; but even in the hard 

 cheeses enzymes alone are incapable of producing a typical 

 ripening. They are aided by the development of micro- 

 organisms and the typical ripening is thus a twofold process. 



It has hitherto been impossible to determine with absolute 

 certainty what kind of microorganisms are concerned in the 

 development of the peculiar character of the hard cheeses. 

 Molds are excluded, since the cheese is so hard that molds 

 cannot grow in its center, and it is commonly salted so 

 highly upon the outside that they are prevented from growing 

 on its surface. Whether yeasts are concerned at all is as yet 

 unknown, although they certainly do play a part in producing 

 certain kinds of abnormal ripening. That bacteria play a 

 part in the ripening is evident. The rapid growth of the lactic 

 bacteria and the disappearance of the peptonizing forms have 

 quite strongly suggested that the former must be regarded 

 as the chief organisms in the process, and most recent experi- 

 ments have indicated that the lactic organisms certainly do 

 play a very important part in the ripening. Cheese made 

 from " aseptic milk " will not ripen, but when inoculated with 

 -certain species of lactic bacteria they ripen in a perfectly 

 normal fashion. Cheese made from pasteurized milk will not 

 ripen, but when inoculated with soured milk, which is nearly 

 a pure culture of lactic bacteria, it ripens in a perfectly 

 normal fashion. 



Of the origin of the flavors of the hard cheeses practically 

 nothing can as yet be said. The lactic organisms have not 

 been shown to produce these peculiar flavors. There are 

 bacteria which laboratory experiments have shown are ca- 

 pable of producing the flavors recognized in various types 

 of cheese (Figs. 33 and 34). These organisms, however, are 

 not yet known to develop in cheeses, and it is by no means 

 certain that they have anything to do with the flavors in the 



