DAIRYING 



other percentages of fat may be found as follows: Cream testing 

 25 per cent, fat contains 75 per cent, serum; and since the fat is a 

 neutral substance the 0.6 per cent, acid is held in the 75 per cent, 

 serum. If we have .6 Ib. acid in 75 pounds serum, there is .6 divided 

 by 75 or .008 Ibs. acid in 1 pound of serum. This .008 pounds acid 

 is then the standard acidity per pound of serum, and the pounds 

 of serum in cream of any per cent, fat should be multiplied by this 

 figure in order to determine the serum acidity, which will corres- 

 pond to .6 per cent, acid in cream testing 25 per cent. fat. 



The results of a few such calculations are given in the follow- 

 ing table: 



Acidity of cream corresponding to .6 per cent, in cream testing 25 



per cent. fat. 



An acidity of any other standard may be calculated by the 

 same method. 



LIMIT OF ACIDITY 



477. It will be explained under the discussion of starters that 

 there is a limit to the percentage of acidity that will develop in 

 either skim milk, milk, or cream. In skim milk this point is 

 reached at about 0.8 per cent, acid ; in cream it will be reached at 

 a lower per cent, acid, depending on the richness of the cream. 



A series of trials have shown that by allowing samples of 

 cream containing from 25 to 50 per cent, fat, to sour several days 

 or until no more acid in quantity would develop, that the limit 

 of acidity obtained was the following: 



Showing the extreme acidity which developed in skim milk and in 

 cream testing different per cents, fat. 



*Too thick to draw into pipette. 



