43<J 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 



