TESTING THE SANITARY CONDITIONS OF MILK 155 



FERMENTATION TESTS IN RELATION TO SANI- 

 TARY CONDITION OF MILK 



Milk frequently contains objectionable forms of 

 organisms or ferments that are not made perceptible 

 by ordinary methods of observation. The condition 

 arises particularly in milk used for cheese-making and 

 may result in serious injury to the quality of the 

 cheese. Several different forms of taste have been pro- 

 posed which will enable one to detect the presence of 

 certain types of organisms through the results of their 

 biochemical action. Of the different forms we will 

 describe two, (i) the Wisconsin test and (2) that of 

 Gerber. 



Wisconsin fermentation or curd test. The Wis- 

 consin Experiment Station (Wis. Exp. Sta. I2th and 

 I5th Annual Reports, 1895 and 1898) has applied cer- 

 tain principles to the development of a test that enables 

 one to identify milk containing certain forms of unde- 

 sirable ferments likely to do serious injury. This meth- 

 od is based, in general, upon the plan of making con- 

 ditions favorable for the rapid development of the fer- 

 ments present in milk. 



Apparatus. The apparatus consists of the follow- 

 ing parts: (i) Pint glass jars or tin cans with covers; 

 (2) a well insulated tank to hold the jars, (3) rennet 

 extract, (4) a thermometer, (5) a case-knife or simi- 

 lar instrument for cutting curd, and (6) a small pipette 

 for measuring rennet-extract. 



Operation of test. The test is conducted as fol- 

 lows: The jars, including covers, just previous to 

 use, are sterilized with live steam, scalding water or 

 dry heat (212 F.). Each jar or can is filled about 



