Bacteria and Cheese Making. 169 



It is desirable for the cheesemaker to obtain as good an 

 idea as possible of the condition of the milk with refer- 

 ence to its bacterial content, since this will determine 

 the rate at which acid will be formed in the curd. If the 

 milk is too sweet, i. e., too low in acid-farming bacteria, 

 a, starter should be added. The only methods by which 

 this information can be obtained by the maker is by de- 

 termining the acidity by the usual method or better by 

 the use of the rennet test by which is ascertained the 

 time required for a. given amount of rennet to curdle a 

 definite quantity of milk at a .standard temperature. 

 The varying factor in the test will be the acidity of the 

 milk. Very slight differences influence profoundly the 

 time of curdling. If, working under standard condi- 

 tions, it is found that the time of curdling of one sam- 

 ple is 10 seconds and of another sample, 20 seconds, it 

 is proof that the acidity of the first is higher than that 

 of the second, that its bacterial content is greater and 

 that acidity will develop in the curd more rapidly. The 

 first may need a small amount of starter, the second a 

 larger quantity. Working with milk from the same 

 source, the maker, from his experience, will know, how 

 much starter should be added to milk that has given a 

 certain result with the rennet test in order that the acid 

 shall be developed in the curd at a desired rate. 



Ripening of cheese. The curd at the time it is put 

 to press is tough and rubbery, and has none of the char- 

 acteristic flavor of cheddar cheese; it is also quite in- 

 soluble and indigestible. Before the cheese is fit to eat 

 it must pass through a complex series of changes which 

 are collectively known as ripening. In these changes 

 there is not only a breaking down of the casein into 

 soluble compounds, which process makes the cheese soft 



