Useful Rules and Tests 357 



Usually it is necessary to propagate the mother starter two or three 

 times before the flavor of the commercial culture, which is often very 

 disagreeable, will disappear. 



A starter may be carried two to four weeks before it goes "off." 

 Often it is carried several months, and often less than two weeks. This 

 depends almost altogether on the carefulness of the operator. 



To DETECT ORDINARY FERMENTATIONS OR "TAINTS" IN MILK 



Procure as many test tubes one inch in diameter by five inches long 

 as there are samples of milk to be tested, and a suitable rack to hold 

 them in an upright position. Wash and rinse the tubes thoroughly and 

 sterilize them by boiling in water for thirty minutes or bv, exposure to 

 live steam in a sterilizing oven for fifteen minutes. After sterilizing 

 they may be allowed to drain dry and then should be kept covered till 

 wanted. When wanted for use the tubes should be filled one-half to 

 two-thirds full with the suspected milk, closed with a piece of glass or 

 plug of cotton and placed in the rack in water kept as nearly constant 

 as possible at 100 F. In from three to four hours the samples may be 

 inspected without shaking or stirring. Gaseous fermentations will be 

 manifested by the appearance of bubbles of gas upon the surface or 

 throughout the mass, souring fermentations by coagulation of the milk 

 and putrefactive fermentations or "taints", by various odors manifest 

 to the nose when the covers are removed. The samples should be kept 

 for at lejist twenty-four hours and examinations made at frequent 

 intervals. 



THE WISCONSIN CURD TEST 



This test is used for the same purpose as the fermentation test 

 described above, and is made as follows: Procure as many covered 

 pint glass jars as there are samples of milk to be tested and clean and 

 sterilize them as described above. Fill each jar two-thirds full of the 

 milk to be tested, label them plainly and put them up to the neck in 

 a tub or vat of water heated to 98 F. When the milk has reached the 

 temperature of the water add ten drops of rennet extract to each jar, 

 and mix it with the milk by shaking the jar. Allow the jars to stand 

 until the curd is firm and then cut the curd finely with a case knife. 

 When the curd has settled pour off the whey and allow the curd to 

 settle again till a second portion of whey can be removed. The best 

 tests are made when the removal of whey is as complete as possible. 

 The jars containing the curd are then covered and again placed in the 



