FARM BUTTERMAKING 115 



of bacteria — good, bad, and indifferent — and to insure a 

 large predominance of tlie lactic acid type in the ripening 

 process, it is necessary to reinforce the bacteria of this 

 type already existing in the cream by adding large quan- 

 tities of them in a pure form, that is, unmixed with un- 

 desirable species. Clean flavored sour milk or skim milk 

 at the point of curdling is practically a pure culture of 

 lactic acid organisms, and the addition of about lo pounds 

 of such milk to every loo pounds of cream will result 

 in a better and more uniform quality of butter. 



Amount of Acid to Develop. Cream of average rich- 

 ness should have an acidity of from 0.5 to 0.6 per cent, 

 when churned. A rich cream requires less acid than a 

 thin cream. 



Sweet and Sour Cream. In small dairies, where only 

 a few churnings are made weekly, care should be taken 

 never to mix sweet and sour cream just before churning. 

 This always results in a heavy loss of fat in the butter- 

 milk on account of the difference in the churnability of 

 sweet and sour cream. 



ACID TEST FOR CREAM. 



Butter makers do not find it safe to rely upon their 

 noses in determining the ripeness of cream for churning. 

 They use in daily practice tests by which it is possible to 

 determine the actual amount of acid present. The method 

 of using these tests is based upon the simplest form of 

 titration, which consists in neutralizing an acid with an 

 alkali in the presence of an indicator which determines 

 when the point of neutrality has been reached. 



In the tests for acidity of cream the alkali used is 

 sodium hydroxide. This is made up of a definite strength 



