MILK AS A FOOD 33 



Variation in composition 



Cow's milk varies greatly in composition. No other or- 

 ganic foodstuff shows such a marked variation except 

 meat. The greatest variation is shown in the butter-fat. 

 The proteins and carbohydrates are more constant. This 

 variation in composition of pure milk is due to a number of 

 different factors, thus: Certain breeds of cows, such as 

 Channel Island breeds, produce a milk rich in fat (about 

 five per cent), while the Holstein stock furnishes a milk 

 relatively poor in butter-fat (about three per cent). Young 

 cows ordinarily produce richer milk than old ones of the 

 same kind. In general a well-fed cow gives more milk and 

 better milk than if poorly fed, but the quantity of the 

 milk is more readily influenced by the amount and char- 

 acter of the food than are the relative proportions of fat, 

 casein, and milk sugar. The milk flow of a given cow is 

 usually largest soon after calving. As the period of lacta- 

 tion progresses, the milk flow gradually falls off and as a 

 rule the milk grows richer in total solids. The proportion 

 of fat to the total solids in the milk of a given cow varies 

 from day to day and even from milking to milking. There- 

 fore it is customary in good dairy practice to mix the milk 

 of several cows immediately after it is drawn. In this 

 way the consumer is assured a more uniform product from 

 day to day. 



Flavors and odors 



The flavor of milk varies almost as much as its composi- 

 tion. Fresh, normal milk is sweet and agreeable and has 

 a very faint animal flavor when warm; this is largely lost 

 upon cooling. Formerly normal milk was supposed to have 

 a "stably" odor, and fastidious persons have been known 

 to reject a glass of clean fresh milk because it did not smell 

 "cowy." A "cowy" taste in milk is often due to absorp- 

 tion of odors in the stable. The dirt that falls into the 



