138 



Testing Milk and Its Products. 



quantity; they are then placed in a water tank, the 

 water of which is heated until the milk in the jars has 

 a temperature of 98 F. In transferring the thermom- 

 eter used from one jar to another, special care must be 

 taken to clean it each time in order to prevent contami- 

 nation of pure lots of milk by impure ones. 



When the milk has reached a temperature of 98, 

 add to each sample ten drops of rennet extract, and mix 

 by giving the jar a rotary motion. The milk is thus 

 curdled, and the curd allowed to stand for about twenty 



FIG. 46. Cross-section of the Wisconsin curd test, T.J-TJ", testing 

 jars showing different stages of test ; WL, water line ; M, milk ; F, 

 frame ; WS, stand to support cover ; AI, drain holes ; WO, water out- 

 let ; DP, drain pail. 



minutes until it is firm. It is then cut fine with a case 

 knife, and stirred at intervals for one-half to three- 

 quarters of an hour sufficiently to keep the curd from 

 matting under the whey. When the cubes are quite firm 

 the whey is poured off and the curd left to mat at the 

 bottom of the bottles if the old form of apparatus is 

 used. The best tests are made when the separation of 

 the whey is most complete. By allowing the samples to 

 stand for a short time, more whey can be poured off, 

 and the curd thereby rendered firmer. The water around 

 the jars is kept at a temperature of 98, the vat is cov- 



