114 MODERN METHODS OF TESTING MILK 



50 cc. glass flask, (4) a thermometer, and (5) a half- 

 pint tin basin. 



In testing the ripeness of milk by means of rennet- 

 extract, one first prepares a dilute solution of the 

 rennet, as follows : One measures with the small pi- 

 pette 5 cc. of rennet-extract into the 50 cc. flask. The 

 pipette is then rinsed twice \vith water by sucking it 

 full of cold, clean water to the mark, the rinsings also 

 being run into the 50 cc. flask. The flask is then filled 

 with water to the 50 cc. mark, and the contents are 

 well mixed by shaking. The next step is to fill the 

 tin cylinder with the well-mixed milk to be tested and 

 this is emptied into the half-pint basin. The milk 

 must be at the temperature at which one adds the 

 rennet in cheese-making, which is generally about 85° 

 or 86° F. To the milk at the desired temperature, one 

 adds 5 cc. of the diluted rennet solution, mixes it 

 through the milk quickly, using the thermometer as 

 a stirrer. The exact time when the rennet-extract is 

 added to the milk is noted by the second-hand of a 

 watch and then again when the milk has coagulated ; 

 the number of seconds required to coagulate the milk 

 is recorded. The exact point of coagulation can be 

 seen more sharply by scattering a few particles of 

 charcoal (as the blackened end of a partly burned 

 match) on the surface of the milk, and then with the 

 thermometer starting the surface into motion around 

 the dish. The black particles stop the instant the 

 milk coagulates. By using a stop-watch, great accu- 

 racy and delicacy can be attained. Care should be 

 taken to keep the temperature of the milk at 85° or 

 86° F., testing frequently with the thermometer ; and, 



