252 AGRICULTURAL BACTERIOLOGY 



CHAPTER XI. 

 BACTERIA IN CHEESE-MAKING. 



METHODS OF MANUFACTURE. 



IN the manufacture of cheese, microorganisms are of even 

 more value than they are in the manufacture of butter. But- 

 ter made from unripened cream has a market, though a small 

 one, but there is absolutely no demand for unripcned cheese. 

 If the changes which take place in the cream during the ripen- 

 ing affect the nature of the butter, the changes which occur in 

 the cheese during its ripening are vastly more profound and 

 more significant. Indeed, it may almost be said that the whole 

 value of cheese is dependent upon its ripening. 



The fundamental phenomena of cheese-making are very 

 simple. Milk is treated in such a manner as to precipitate the 

 casein in the form of a curd. Commonly this is done by add- 

 ing rennet to the milk, but in some forms of cheeses, the casein 

 is thrown down by acid, the usual method being simply to al- 

 low the milk to sour, depending upon the lactic acid formed 

 to produce the normal curdling. After the curdling, the solid 

 curd is separated more or less from the liquid and the curd is 

 placed in moulds for shaping and pressing. The amount of 

 liquid left in the curd differs for different types of cheeses. 

 After it is shaped in the moulds the cheese mass is set aside, 

 under constant conditions of temperature, to undergo the proc- 

 ess of ripening. It is the ripening which produces the changes 

 in the cheese and which gives its typical character. With these 

 ripening changes we are concerned in our study of bacteria. 



Soft Cheeses. There are two quite different types of cheeses, 



