138 



Testing Milk and Its Products. 



and into which a rack fits, holding a certain number of cylin- 

 drical glass tubes; these are all numbered and provided with a 

 mark and a tin cover. 

 In making the test, the 

 tubes are filled to the 

 mark with milk, the num- 

 ber of each tube being 

 recorded in a note book, 

 opposite the name of the 

 particular patron whose 

 milk was placed therein. 

 The tubes in the rack are 

 put in the tank, which is 

 two-thirds full of water; FlG - 47 - The Gerber fermentation test, 

 the temperature of the water is kept at 104-106 F., for 

 six hours, when the rack is taken out, the tubes gently shaken, 

 and the appearance of the milk, its odor, taste, etc., carefully 

 noted in each case. 



The tubes are then again heated in the tank at the same tem- 

 perature as before, for another six hours, when observations of 

 the appearence of the milk in each tube are once more taken. The 

 tainted milk may then easily be discovered by the abnormal 

 coagulation of the sample. According to Gerber, 1 good and prop- 

 erly handled milk should not coagulate in less than twelve hours, 

 when kept under the conditions described, nor show anything 

 abnormal when coagulated. Milk from sick cows and from cows 

 in heat, or with diseased udders, will always coagulate in less 

 than twelve hours. If the milk does not curdle within a day or 

 two, it should be tested for preservatives (299). 



157. The Monrad rennet test is used by cheese mak- 

 ers for determining the ripeness of milk. Fig. 48 shows 

 the apparatus used in the test. 5 cc. of rennet extract 

 is measured into a 50 cc. flask by means of a pipette; 

 the pipette is rinsed with water, and the flask filled to 

 the mark with water. 160 cc. of milk is now measured 

 into the tin basin from the cylinder and slowly heated 

 to exactly 86 F. 5 cc. of the dilute rennet solution is 



Die praktische Milchpriifung, p. 85. 



