METHODS USED IN 



THE EXAMINATION OF MILK AND 



DAIRY PRODUCTS 



PART I MILK 



INTRODUCTORY 



MILK is, as is well known, the secretion of the mammary glands 

 of mammalia, and in this volume, wherever the word milk is 

 employed alone, it will be understood to apply to the milk 

 of the cow, for this is much more important, for domestic 

 purposes, than the milk of any other animal. 



Milk which is secreted by a healthy udder is an opaque, 

 white emulsion with a porcelain-like appearance. Sometimes 

 it has a tinge of yellow or blue, according to the amount of 

 fat and the deeper or lighter colour of the fat. Milk is trans- 

 parent only when in very thin layers. The taste of milk is 

 satisfying, pleasant, and somewhat sweet, and the smell is 

 reminiscent of the animal, but not unpleasantly so. 



Milk is heavier than water, the specific gravity lying between 

 1-029 and T033, according to Fleischmann, 1 when the sample is 

 taken from five or more cows, or when it is from two or three 

 milkings. The milk of individual cows or that from a single 

 milking has a specific gravity between T028 arid T034. It 

 may be taken that the average specific gravity is T0315 when 

 determined, as in the above cases, at a temperature of 15 C. 



The viscosity of milk compared with water is 220 : 100 at 0, 

 whilst at 30 it is 170 : 100. There is a considerable increase 

 of viscosity at the lower temperatures, and on that account the 

 foam which forms on the surface of cold milk persists for a 

 long time. 



1 Lehrbuch der MilchwirtHchaft. Fourth Edition. Leipsic, 1907. 



B 



