MARKET MILK 151 



marvelous rapidity. The proteids and milk-sugar are most 

 easily broken down, causing changes in chemical composition 

 and the production of by-products which affect the commercial 

 value of the milk. The most common change is the souring 

 of the milk caused by the breaking down of the milk-sugar and 

 the formation of lactic acid. Many other changes are caused 

 by the growth of bacteria and yeasts, such as ropy or slimy 

 milk, gassy milk, sweet curdling and a large variety of bad 

 flavors and odors which seriously affect the value of the 

 milk. 1 



The question of cleanliness is becoming more and more im- 

 portant in the production and handling of market milk. This 

 is because it has been clearly shown that there is a definite 

 relation between cleanliness and wholesomeness of the product. 

 In its generally accepted meaning, milk cleanliness involves not 

 only the presence or absence of visible dirt but also of micro- 

 organisms and the decomposition products resulting from their 

 action. 



If fresh milk contains a large number of bacteria, it indicates 

 that the milk has become contaminated during the process of 

 milking. 2 



If milk contains large numbers of bacteria when it reaches 

 the consumer, either it is not fresh, has come from a diseased 

 cow, or has otherwise been contaminated, or it has not been 

 kept cook Although such milk may contain no visible dirt, it 

 is not bacteriologically clean and should not be sold as clean 

 milk. 



By exercising proper care, the number of bacteria which get 

 into milk during the process of milking may be kept very low 

 and their subsequent growth largely prevented by immediate 

 cooling and holding at low temperatures. 



1 For a fuller discussion of this subject, see chapter on Relation of 

 Bacteria to Dairy Products. 



2 Adapted from U. S. Bui. 602. 



