10 -i Dairy Bacteriology. 



Milk when drawn from the cow has an apparent acidity 

 ranging from 0.16 to 0.18 per cent. By the use of any 

 of the methods of determining acidity in milk, much can 

 be told concerning the number of bacteria in the milk, 

 and hence concerning its keeping quality. Milk that has 

 an acidity of over 0.2 per cent is certain to contain many 

 bacteria, and consequently will keep poorly. Such milk 

 is of low value for market milk, but may not be objec- 

 tionable for butter or cheese making. If the acidity is 

 below 0.2 per cent, but little can be told as to the num- 

 bers of bacteria, since any increase in acid is always 

 preceded by an enormous increase in the numbers of 

 acid-forming bacteria. 



A more important test than the acid test, from the 

 standpoint of the butter and cheese maker, and even the 

 milk dealer, is the fermentation test. In its simplest 

 form, it consists in placing a sample of the milk to be 

 tested in a warm place and noting the time required to 

 curdle and the type of curd formed. In this country the 

 fermentation test has been largely supplanted by the 

 "Wisconsin curd test which possesses the advantage of 

 detecting the presence of bacteria harmful in cheese 

 making, especially the gas forming bacteria. 



The curd test is helpful in detecting the source of an 

 abnormal condition in a milk supply coming from diverse 

 sources. The milk furnished by each patron can be 

 tested separately and the trouble located, perhaps in an 

 individual herd; the offending herd determined, the test 

 may then be used on the milk of individual cows. The 

 cheese maker and the milk dealer should be able not only 

 to detect which of the patrons furnish him poor milk, 

 but he should be able to give the patron definite instruc- 

 tions how to avoid the sources of such trouble. This in- 



