26 Testing Milk and Its Products. 



32. Sampling sour milk. When milk becomes sour, 

 the casein is coagulated and the mechanical condition of 

 the milk thereby changed so as to render difficult a cor- 

 rect sampling. The butter fat is not, however, changed 

 in the process of souring; this has been shown by one 

 of us, among others, in a series of tests which were 

 measured from one sample of sweet milk into six test 

 bottles. A test of the milk in one of these test bottles 

 was made every month for six months, and approxi- 

 mately the same amount of fat was obtained in the 

 tests throughout the series, as was found originally in 

 the milk when tested in a sweet condition. 1 If the milk 

 is in condition to be sampled, its souring does not there- 

 fore interfere with its being tested by the Babcock test 

 or with the accuracy of the results obtained. 



In order to facilitate the sampling of sour or lop- 

 / pered milk, some chemical may be added which will re- 

 dissolve the coagulated casein and produce a uniform 

 mixture that can be readily measured with a pipette. 

 Any alkali (powdered potash or soda, or liquid ammo- 

 nia) will produce this effect. Only a very small quan- 

 tity of powdered alkali is necessary for this purpose. 

 The complete action of the alkali on sour milk requires 

 a little time, and the operator should not try to hasten 

 the solution by adding too much alkali. An excess of 

 alkali will often cause such a violent action of the sul- 

 furic acid on the milk to which the acid is added (on 

 account of the heat generated or the presence of car- 

 bonates in the alkali) that the mixture will be thrown 



l See Hoard's Dairyman, April 8, 1892. The same holds true for 

 cream, as shown by Winton (U. S. Dept. Agr., Div. of Chemistry, bull. 

 48, p. 112). 



