132 MANUAL OF MILK PRODUCTS 



TESTING SOUR MILK (Ross) 



• 



Sour milk should not be tested unless such testing is abso- 

 lutely necessary. It is difficult to test sour milk because the 

 casein has been precipitated and the fat is locked up in the 

 particles of curd, making an even distribution of the fat impos- 

 sible. The consistency of sour milk can be made more like 

 that of normal milk by the addition of strong alkali, which 

 drives, or tends to drive, the casein into suspension. The 

 particles of fat are then released. Caustic soda and caustic 

 potash are useful in restoring the consistency of sour milk, and 

 it is best to add them in the dry form because, when so used, 

 they do not dilute the milk to any appreciable extent and it is 

 unnecessary to make any correction when reading the fat column. 

 If a liquid alkali is used, the milk is diluted and a corresponding 

 correction must be made when the fat column is read. 



TESTING CHURNED MILK (Ross) * 



Churned milk should not be tested if it can be avoided. 

 When it is absolutely necessary to test churned milk, the milk 

 should be heated to about 85° F. and well shaken, and the 

 sample should be drawn quickly. If the sample is badly 

 churned, enough ether should be added to dissolve the fat. 

 After thoroughly mixing, the sample is drawn, the ether is 

 evaporated, and the quantity of ether taken is weighed. 

 The sample is then tested in the usual manner, a correction in 

 the reading being made for the quantity of ether used. 



ACIDITY OF MILK 2 (Ross) 



The acidity of milk is of two kinds — apparent and real 

 acidity. The apparent acidity is due to the acid reaction of 



1 C. U. Bui. 337. 



2 A Dairy Laboratory Guide, Orange Judd Co. 



