31 



[Suggestion to lecturer: Have apparatus for both of these tests. 

 Perform tests before students and then liave each student perform 

 the tests. Use milks of dilTerent age in the test. Have differont stu- 

 dents compare results on the same sample of milk.] 



4. Detection of injurious ferments in milk. — The "Wisconsin curd 

 test" is a method for detecting milks that are undesirable for cheese 

 making (reference No. 3, p. 64, or No. 8, p. 15). The test con- 

 sists in making a small chunk of cheese curd from milk in a glass jar. 

 Pint fruit jars with small holes in the covers are sterilized in boiling 

 water and then nearly filled with the milks to be tested and placed in 

 water at 95° to 100° F. Ten drops of rennet are added to each jar 

 and mixed. After curdling, the curd is cut into small pieces and 

 stirred, the whey being poured off from time to time until the curd 

 mats. The curd is then kept at about 95° F. for six or eight hours 

 and then examined. Injurious forms of ferments in milk are indi- 

 cated when the curd is spongj' in texture and very full of holes or 

 "mushy" in texture or offensive to smell. This test is of value in 

 detecting individual herds and even individual cows, whose milk is 

 not good for cheese making. 



[Suggestions to lecturer: This test should be performed on different 

 milks, some of which have been treated so as to be made bad. Each 

 student should be re(|uired to perform the details untiL they are 

 familiar. Every milk used in cheese making l)y the students should 

 be examined by this test, and it should be applied at times to the milk 

 of each herd.] 



5. The hot-iron iesf.— (References No. 3, p. 74, and No. 8, p. 61.) 

 The hot-iron test is a means of measuring roughly the amount of 

 paracasein that has been formed from calcium paracasein or of the 

 amount, of acid that has been formed and combined with calcium of 

 calcium paracasein. It does not indicate the amount of acid present 

 in the whey. The test is made as follows: A small mass of curd is 

 pressed in the hand to remove the whey and is then pressed against 

 a bar of iron heated a little short of redness and then drawn away 

 carefully. Fine silky strings adhere to the iron, the length depending 

 mainly on the amount of free paracasein present in the curd. Sam- 

 ples of pure paracasein may be drawn out in strings a foot or more 

 long when tested by the hot iron. Uncombined casein behaves the 

 same way (reference No. 1, pp. 16, 28). 



EXPERIMENT AND PRACTICE WORK, FIFTH LECTURE. 



Time required. — Four hours can well be devoted to work on the dif- 

 ferent tests described, getting familiar with details, so that one can 

 apply them daily in regular work. 



AiJparatus and materials required. — (1) Quevenne lacto-thermome- 

 ter, (2) New York State Board of Health lacto-thermometer, (3) glass 



