J3acteria in Cheese. 163 



then practically all abnormal conditions could be controlled 

 by the use of properly selected starters. Numerous at- 

 tempts have been made to perfect this system with refer- 

 ence to cheddar cheese, but so far they have been attended 

 with imperfect success. The reason for this is that in pas- 

 teurizing milk, the soluble lime salts are precipitated by the 

 action of heat, and under these conditions rennet extract 

 does not curdle the casein in a normal manner. This con- 

 dition can be restored, in part at least, by the addition of 

 soluble lime salts, such as calcium chlorid; but in our ex- 

 perience, desirable results were not obtained where heated 

 milks to -which this calcium solution had been added were 

 made into cheddar cheese. Considerable experience has been 

 gained in the use of heated milks in the manufacture of cer- 

 tain types of foreign cheese. Klein 1 finds that Brick cheese 

 can be successfully made even where the milk is heated as 

 high as 185 F. An increased weight is secured by the addi- 

 tion of the coagulated albumin and also increased moisture. 

 Bacteria in rennet. In the use of natural rennets, such 

 as are frequently employed in tbe making of Swiss cheese, 

 considerable numbers of bacteria are added to the milk. Al- 

 though these rennets are preserved in salt, alcohol or boric 

 acid, they are never free from bacteria. Adametz 8 found 

 ten different species and from 640,000 to 900,000 bacteria 

 per cc. in natural rennets. Freudenreich has shown that 

 rennet extract solutions can be used in Swiss cheese-mak- 

 ing quite as well as natural rennets; but to secure the best 

 results, a small quantity of pure lactic ferment must be 

 added to simulate the conditions that prevail when natural 

 rennets are soaked in whey, which, it must be remembered, 

 is a fluid rich in bacterial life. 



* Klein, Milch Zeit. (Hildesheim), No. 17, 1900. 

 8 Adametz, Landw. Jahr., 18:256. 



