40 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- 
