Fermentations of Milk. 



105 



formation can be given only when the source is positively 

 known. 



The Wisconsin curd test is made as follows: Samples 

 of the milk to be tested are placed in sterile pint fruit 





FIG. 23. CURD TEST. 



A good curd obtained from milk containing no harmful bac- 

 teria but many desirable acid-forming organisms. 



jars. The milk is warmed to 90 F., ten drops of rennet 

 are added to each sample, and as soon as the curd is 

 solid, it is cut into small pieces with a case knife so as 

 to facilitate the expulsion of the whey. As the curd set- 

 tles to the bottom of the vessel, the whey is poured off 

 at intervals so that a pat of firm curd is left. As the 

 milk curdles the bacteria are enmeshed and are carried 



