RECEIVING, SAMPLING, AND GRADING. 81 



less than .3% of acid, etc. By means of such a test the acidity 

 can quickly be determined. 



The sample cups should be numbered to correspond with 

 the number of each patron. The results of the tests should 

 be noticed at once, as the action of the atmosphere affects 

 the color. 



The acid tests are of value in grading cream, as a sour 

 sample of milk or cream is either old or has been improperly 

 kept and handled. The number of grades of cream and milk 

 and the maximum limit of acid each grade can contain, are 

 factors which must be decided according to local conditions, 

 by the operator. 



3. Use of the Fermentation Tests. — Curdled, ropy, red and 

 blue milk can, as a rule, readily be detected without the appli- 

 cation of a special test, but there are cases when a person's 

 senses are not sufficiently acute to detect samples of milk 

 containing undesirable fermentations. Several instances have 

 recently come within the authors' notice. A neighboring 

 creamery was infested with a peculiar fermentation that 

 caused a -\'ery rank flavor in the butter. The milk that came 

 to the creamery was carefully examined, but without locating 

 the source of the trouble. The cause could not be ascertained 

 without the use of the fermentation test. 



It is in such instances that a fermentation test is of special 

 value. As a rule, at least when the trouble first begins, it is 

 milk from one particular patron that causes the trouble. 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 Tets. — 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.— This test consists of properly made glass 

 tubes which fit into a rack. This rack, containing the bottles, 



