43^ SCIENCE AND PRACTICE OF CHEESE-MAKING 



development of a test that enables one to identify milk- 

 containing certain forms of undesirable ferments likely 

 to do serious injury. This method is based, in gen- 

 eral, upon the plan of making conditions favorable for 

 the rapid development of the ferments 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 sim- 

 ilar 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 

 two-thirds full with the milk to be tested and the ster- 

 ilized cover put on at once. The jars are then placed 

 in the tank which is filled with water at 100 to 102 

 F. up to the upper surface of the milk in the jars. The 

 temperature of the water should be kept at 100 to 

 102 F. during the whole operation. To hasten the 

 warming of the milk, the jars are taken out and shaken 

 occasionally. The temperature of the milk is observed 

 with a sterile thermometer, and when the milk has 

 reached 98 F., one adds 10 drops of rennet-extract 

 to each jar and mixes thoroughly by giving the con- 

 tents of the jar a rotary motion. When the milk has 

 coagulated, it is allowed to stand until it is firm, usu- 

 ally about 20 minutes. To enable the whey to sepa- 

 rate more readily, the curd is then cut fine with a 

 thin knife, which must be carefully rinsed with hot 

 water after finishing each jar and before using it in 

 another, in order to avoid carrying contamination from 



