92 Dairy Bacteriology. 



Sweet curdling fermentation of milk. Samples of 

 milk are sometimes found that are curdled, but which do 

 not taste sour, or have the normal' odor of sour milk. 



FIG. 21. DIFFERENT TYPES OF CURDS. 



The flask on the left shows the soft curd produced by the bac- 

 teria that curdle the milk without the production of acid. 

 The flask on the right shows the gassy curd formed by bu- 

 tyric acid bacteria in heated milk. 



The curd is usually soft and the taste bitter. It is evi- 

 dent that the curdling cannot be due to the same factors 

 as in the normal souring of milk. Such a change is sim- 

 ilar to the action of rennet which is used to curdle the 

 milk in cheese making. This ferment will curdle per- 



