34 MARKET DAIRYING 



dred times faster than at 70° F. At 32° F. bacterial de- 

 velopment practically ceases. 



Milk or cream may be kept sweet a long time at 40" 

 to 45° F. because the lactic acid bacteria practically stop 

 growing at these temperatures. But there are other 

 classes of bacteria that can grow at these temperatures, 

 as evidenced by the production of undesirable flavors. 

 Such flavors usually become noticeable after thirty-six 

 hours. Where milk and cream are to be kept in the best 

 possible condition, it is necessary to reduce the tempera- 

 ture to within a few degrees of freezing. 



Lack of thorough cooling necessitates two deliveries of 

 milk per day, and, what is still worse, requires many 

 dairymen to milk their cows shortly after midnight and 

 shortly after midday, a drudgery which casts a damper 

 upon the whole milk business. Lack of cooling also means 

 financial loss through souring of milk and leads to many 

 dissatisfied customers. 



Prompt Cooling. Milk should be cooled as quickly 

 as possible after it is drawn. Indeed, the milk should be 

 taken directly from the cow to the cooling room and 

 promptly cooled. To do this conveniently it is necessary 

 to have the cooling room located as near the barn as is 

 consistent with freedom from barn odors. 



Too often the milk is allowed to remain in the barn 

 until all the cows have been milked, and this may require 

 from two to three hours, depending upon the number 

 of cows milked by each milker. A few hours delay in 

 cooling reduces the keeping quality of milk to a far greater 

 extent than is commonly supposed. 



Importance of Aeration. Milk not only con- 



tains bacteria immediately after it is drawn, but it 

 also contains gases, chief among which, perhaps, is car- 



