in CHEESE 193 



for the test. Five c.c. of the rennet solution, or 5 g. of the 

 rennet powder are made up to 100 c.c. with distilled water. 

 After well mixing, 10 c.c., equivalent to 0'5 c.c. or 0'5 g. of the 

 rennet preparation, are drawn off with a pipette and run into 

 500 c.c. of perfectly fresh milk, warmed to 35 C. and the exact 

 time, to a second, noted when the two liquids are brought to- 

 gether. The solution of rennet is blown with force into the 

 milk so that it is uniformly distributed and then the whole is 

 well and quickly shaken round. As will easily be seen there is 

 now one part of the rennet preparation 1 c.c. or 1 g. to each 

 1000 c.c, of milk. A thermometer which has previously been 

 placed in the milk is moved gently to and fro, and the length 

 of time which elapses before coagulation is apparent is noted. 

 This point is indicated by the appearance of fine particles 

 of milk behind the thermometer. The temperature of the 

 milk must be kept as nearly as possible at 35 C., during 

 the determination. If, for example, the time required for 

 coagulation is found to 5 '5 5 minutes, the quantity of milk (x) 

 which would be coagulated in 40 minutes at the same tempera- 

 ture by a similar quantity of rennet would be : 



5-55:40=1,000:0? 



x = 7,207 



The rennet preparation thus tested is found to have 

 a strength of 1 : 7,207 or in round numbers 1 : 7,200. 



Rennet powders which act more energetically are tested by 

 taking 1 g., dissolving it in 200 c.c. of water, allowing it to stand 

 for at least a quarter of an hour, and then, after well stirring 

 up, 5 or 10 c.c., according to circumstances, are allowed 

 to act upon 500 g. of new milk at 35 C. The proportion of 

 rennet to milk ought to be either nearly 1 : 20,000 or 1 : 10,000. 

 If for instance the proportion of rennet to milk had been 

 1 : 20,000 and the coagulation period again 5'55 minutes 

 (5 minutes, 55 seconds) then the quantity of milk x which 

 would be coagulated at the same temperature in 40 minutes 

 by 1 part of rennet would be, 



5-55 : 40 = 20,000 : x 

 x = 144,144 



or in other words, the strength of the rennet powder is 

 in round numbers 1 : 144,000. This method of testing rennet 



o 



