No. 6. DEPARTMENT OF AGRICL'LTUP.P:. 607 



about i)~) decrees F. to 100 degrees F, Then ten droi>s of reon»;t 

 extract are added to the milk in each jar and the conteotH are thor- 

 onghlj mixed. The milk ia then left undisturbed until comi>Ietely 

 curdled, after which it is cut in small pieces with a case koife and 

 stirred in order to ex[)el the whey. Care must be taken to dean 

 the knife each time before cutting the curd in each jar. The whey 

 is poured off at frequent intervals, until the curd mats. The curd 

 is then kept at a temperature of about 08 degrees F, for six or eight 

 hours and then examined. If the milk is good, the curd from it 

 has a solid, firrn texture, with (m]y a few small pin-holes, if any. 

 It may have some large, irregular holes caused mechanically by the 

 failure of the particles of curd to unite closely. If gas-forming bac- 

 teria are present in the milk, they will produce a curd of spongy tex- 

 ture, very full of holes. Other undesirable fermentations may show 

 their presence by producing a curd of soft, "mushy" texture, while 

 others develop offensive odors. By the use of this test, it is easily 

 possible to detect what patron's milk is the source of trouble, op, 

 in the case of a herd, what individual cow or cows. When un- 

 favorable fermentations are met with in factory ex-perience, this test 

 should be promptly and thoroughly applied, and milk found to be 

 responsible for the trouble should be excluded until its character 

 is improved. Also, milk should not be received for cheese-making 

 when it contains as much as two-tentlis of one per cent, of lactic acid. 

 This curd test may also be applied to the examination of market milk 

 that is sold for direct consumption. 



49. Hource aod Properties of Rennet Extract. 



AV'e have already (see section 0, p. 564) refei-red to rennet as con- 

 taining an enzyme or unorganized ferment, called rennet, which 

 possesses the characteristic property of coagulating or solidifying 

 milk-casein, and, on this account, lies at the basis of our cheese- 

 making, Rc-cnet is used in the form of an extract, 



(1.) Source of Rennet Extract. — The usual source of rennet is the 

 fourth stomach of a calf that has not stopped living upon milk. 

 The enzyme is separated from this by special tratment, such as 

 soaking in dilute salt water. For cheese-making purposes, it is 

 much preferable to purchase one of the regular commercial rennet 

 extracts rather than to use a home-prepared article. The best 

 brands of commercial extracts are uniform in strength and free 

 from taints, and this is not commonly true of home-prepared ex- 

 tracts. Rennet extract should be kept in a cool, dark place, if it is 

 to keep its strength for the longest possible time. 



