610 ANNUAL REPORT OF THE Off. Doc. 



tides of charcoal on tlie surface of the milk. The railk is started into 

 motion around the dish by stirring with the thermometer, and the 

 charcoal particles stop the instant the milk curdles. By using a 

 stop watch in carrying out this test, great accuracy and delicacy 

 can be attained. In comparing two rennet extracts by this test, 

 the one that coagulates the milk in the quickest time is the strongest. 

 If possible, the same kind of milk must be used in comparing differ- 

 ent extracts. (See Fig. 3.) 



(2.) The Marschall Rennet Test. — In this test, the same general 

 plan is followed, but the coagulation takes places in a cup on the 

 sides of which are some graduated lines, while in the bottom of the 

 cup is a glass tube, with very small bore." After the rennet is 

 added to the milk in the cup, this fine glass tube is opened and the 

 milk allowed to trickle away, until the railk coagulates and ceases 

 to run. The marks on the inside of the cup show how much milk 

 has run out and the number of spaces uncovered show the strength 

 of the rejinet. The stronger the action of the rennet, the more 

 quickly is the milk coagulated and the less runs out and the fewer 

 spaces are uncovered. There are some objections to this test, which 

 should be noted. A difference in the bore of the glass tube in 

 the bottom of the cup makes a great difference in results, and it 

 is found that the bore differs in different cups. In trying different 

 cups, always compare them on the same sample of milk. While 

 the ]\farschall test is coovenient for ordinarv factorv work, it is 

 not capable of as great delicacy as is the Monrad test and, therefore, 

 is not so well suited for work requiring extreme precision. 



51. Ripening Milk for Cheese-Making. 



In ripening milk for cheese-making, the aim is, as in the case 

 of ripening cream, to encourage the fermentation of lactic acid, but 

 in a lesser degree than io cream. Let us first consider how we 

 ripen milk for cheese-making and then how we determine when we 

 have ripened milk enough. 



(1.) How to Ripen Milk. — Lactic acid may be formed in milk simply 

 by heating the milk to 82 degrees F. to 86 degrees F., and allow- 

 ing it to stand awhile. This temperature favors the rapid growth 

 of the lactic acid bacteria already in the milk and the fermenta- 

 tion of the lactic acid takes place quite promptly in ordi«ary factory 

 milk. Th( re are times, however, when either lactic acid organisms 

 are not abundant or other injurious forms of ferments are so abund- 

 ant as to repress the growth of the acid-formers, and, under such con- 

 ditions, it is unwise to wait for the development of the acid bacteria. 

 The method is then to develop lactic acid by adding a starter. A 

 starter prepared as described in section 27, p. 584, may be used, or 



