40 THE BOOK OF BUTTER 



32. Conditions of growth. — Like other forms of plant 

 Hfe, bacteria require moisture, warmth, and food. Unlike 

 most plants, they do not require sunlight. In fact, the 

 direct rays of the sun are very injurious to them. To 



prevent the de- 



Not wiped 



Wiped 



Disease due to 

 wiping 



7,058 bacteria 



716 bacteria 



^^^^^^m velopment of 

 bacteria, it is 

 necessary either 

 to kill them by 

 pasteurization 



6,342 bacteria or in somc cases 



by sterilization ; 



Fig. 10. — Showing the decrease in bacteria-content ^^ ^^ change One 

 of the milk due to wiping the cow's udder with of the essential 

 a damp cloth immediately before millcing. requirements of 



their growth. The only method that is practicable on 

 the farm is the usual custom of putting the temperature 

 down to such a point that the bacteria will not grow. It 

 at least consists in cooling the milk to such a degree that 

 their development is slow. 



33. Reasons for cooling milk. — The principle of 

 cooling applies in the same way to cream as to milk. 

 Regarding the cooling of milk Stocking ^ says : 



" After we have taken as much care in producing the 

 milk as we can, there will still be some bacteria in it, 

 and these should be prevented from growing by imme- 

 diately cooling the milk to such a degree that their develop- 

 ment will be checked. The more quickly milk can be 

 cooled to a temperature of fifty degrees or lower, the 

 slower will be the development of the bacteria. The effect 

 of temperature upon milk is strikingly shown bj^ the 



• Stocking, W. A., Jr., Problems of the Milk Producer, New 

 York State Dept. of Agri., Cir. 10, p. 62, 1910. 



