RECEIVING AND GRADING OF MILK AND CREAM 95 



particular patron. This milk may appear to be normal, and yet 

 contain germs which are very undesirable for the manufacture of 

 the best quality of butter. 



Fermentation Tests. There are two tests which may be of 

 general use; namely, the " Wisconsin Curd Test" and the 

 " Gerber Fermentation Test." The former is used in cheese 

 factories, but the latter is to be recommended in testing milk for 

 butter-making. 



Gerber Test. The apparatus for this test consists of properly 

 made glass tubes resting upon a rack which fits into a small 

 round tin tank, about two-thirds full of water. The temperature 

 of this water can be controlled by means of a lamp kept burning 

 underneath, or by the use of steam. The milk delivered by dif- 

 ferent patrons is put into the glass tubes, and these are numbered 

 so as to indicate to which patron each belongs. The tempera- 

 ture should be kept at about 104 to 106 F. for about six hours. 

 Then the tubes are taken out, the milk shaken, and the appear- 

 ance, smell, and taste of the milk noted. The tubes are warmed 

 again for about another .six hours, when they are again examined. 

 If any samples contain a preponderance of abnormal ferments, 

 the fact will usually appear in less than eighteen hours. If 

 milk does not coagulate in twelve hours, or become abnormal 

 in some way, it is considered good. 



The special apparatus mentioned above is not absolutely 

 essential, nor is the temperature employed considered by the 

 authors to be the most suitable to give reliable results. Ordinary 

 sample jars can be used, instead of specially prepared tubes. 

 After the milk has been placed in the jars they can be kept in any 

 convenient place, at a temperature of about 98 F. The best 

 place to keep them is in a vessel containing water, the temperature 

 of which can be controlled. 



Wisconsin Curd Test. This test consists of taking some milk 

 in a jar and adding about ten drops of rennet, which coagulates 

 the milk. The sample is allowed to stand until the curd hardens, 

 when it is cut into small pieces with a case knife; the whey is 

 drawn off, and the curd allowed to stand at a temperature of 

 98 F. If there are any undesirable forms of bacteria present, 



