94 GRADING AND TESTING MILK AND CREAM 



2. The Use of Acid Tests. Some creameries are now grading 

 the milk or cream according to the amount of acid it contains. 

 Mann's and Farrington's acid tests can both be used, but a more 

 rapid and convenient way is to use a solution prepared from Far- 

 rington's tablets. The solution is prepared by dissolving the 

 tablet in warm water, using an ounce of water to a tablet. When 

 one part of this alkaline solution and one part of milk are mixed 

 together in a cup and the solution still retains a pink color, it shows 

 that there is less than .1 per cent acid in the sample tested. If 

 two parts of alkali and one part of milk are mixed and the mixture 

 remains pink, then there is less than .2 per cent of acid. If the 

 mixture becomes colorless, it shows there is more than .2 per cent 

 acid in the sample. If three measures of alkali to one measure 

 of milk are taken, and the mixture remains pink, there is less 

 than .3 per cent 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 max- 

 imum 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, be readily 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 con- 

 taining undesirable fermentations. Several instances have 

 recently come within the authors' notice. A neighboring cream- 

 ery was infested with a peculiar fermentation that caused a very 

 rank flavor in the butter. The milk that came to the creamery 

 was carefully examined, but the source of the trouble could not 

 be located. 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, the trouble is first caused by milk from one 



