FERMENTATION TEST. 243 



temperature of 90^ and allowed to remain at this tem- 

 perature for some six hours. At this high temperature 

 the gas-producing organisms develop rapidly, as well as most 

 other organisms which are liable to produce bad flavors. At 

 the end of six hours the samples are examined, and if it is 

 found that the milk has soured and curdled into a smooth 

 hard curd, without improper odors or a considerable produc- 

 tion of gas bubbles, the milk is regarded as normal and used 

 unhesitatingly. If, however, any sample of milk should be 

 found to be rilled with bubbles of gas, or if it should show 

 any unpleasant and strongly penetrating odors, the milk is 

 regarded as suspicious, and should be excluded from the milk 

 which is to be manufactured into cheese. It is found that 

 milk which sours and curdles into a hard, smooth curd, may 

 be regarded as quite sure to make a type of cheese which will 

 not become unduly swelled, while those samples in which 

 gas bubbles appear in great abundance in this fermentation 

 test are suspicious and must be excluded if the cheese-maker 

 wants to avoid the possibility of obtaining inflated cheese. 



An improvement over this is the so-called curd test (256). 

 In this test small jars are half filled with each milk to be 

 tested, heated to 98 C. and rennet is added. The curd 

 formed is cut to pieces and the whey allowed to drain off. 

 The curd is then kept at a warm temperature to allow the 

 bacteria to gro.w. The character of the curd, after a few 

 hours, makes it possible to determine whether the milk con- 

 tained too many gas-forming bacteria, which show their pres- 

 ence by filling the curd full of holes, as shown in Fig. 35. 

 The application of this test has proved to be of practical 

 value to cheese-makers in locating and remedying the cause 

 of imperfections in cheese ripening. 



Finally, there have been some successful attempts at avoid- 

 ing this difficulty by inoculating the milk which is to be used 

 for cheese-making with a satisfactory culture of lactic bac- 

 teria, the proper species of lactic bacteria being capable of 



