BACTERIA. 165 



so that they produce an article highly flavored and 

 of a standard quality. 



As soon as the butter is made, most of the bac- 

 teria die, probably on account of the small amount 

 of water and the presence of a great deal of 

 salt. 



Some, however, remain alive. These, after a 

 while, cause the butter to change its character and 

 become rancid. Butter, to keep well, should have 

 all of the water worked out, and a large amount of 

 common salt mixed with it. Salt kills bacteria in 

 butter just as it does in meat. 



Cheese-making is also dependent upon the 

 growth of bacteria. Cheese is made from the 

 casein of milk. This is separated from the other 

 products by rennet. After being separated, the 

 casein is pressed into a solid mass of the shape 

 and size desired, and then set away in a moderate 

 temperature to ripen. It takes weeks, sometimes 

 months, for cheese to ripen, depending upon the 

 kind and the influencing conditions. The slow- 

 ness of the process is probably due to the fact 

 that a great deal of water is pressed from the mass 

 in reducing it to a solid condition. 



Often bacteria different from the ones desired 

 get into cheese. These so change the product as 

 to make it unfit for use. The cheese-maker can- 

 not always control the germs in his cheese so as to 

 produce grades of uniform quality and flavor; but, 

 with care, most of the difficulties can be overcome. 



