BACTERIOLOGY OF BUTTER 423 
cation of certain bacteria. The pasteurized milk was found to be more 
favorable to the attack of the gas forming colon bacillis and B. aerogenes. 
Allen emphasizes the point that pasteurized milk, although it is safer 
for human consumption, should be handled with much care since heating 
has decreased its resistance to many detrimental changes. Ayers and 
Johnson after a study of this question reported that the bacterial 
increase in clean raw milk and pasteurized milk was about the same 
when both were stored under the same conditions. 
BACTERIOLOGY OF BUTTER 
The bacteriology of butter may be considered from two viewpoints— 
the use of bacteria to bring about desired changes and the dissemination 
disease-producing bacteria. 
Bacteria in Cream and Cream Ripening. According to present 
practice cream is pasteurized and ripened before being made into butter. 
The pasteurization process removes all of the extraneous bacteria and 
thus prevents spontaneous changes which are liable to produce unfavy- 
orable flavors and tastes. After pasteurization, the cream is inoculated 
with a culture known to produce a desired flavor and allowed to ripen. 
Certain distinct improvements were introduced into the butter industry 
by ripening of the cream. (1) A better yield of butter is secured from 
sour cream. (2) The flavor of the butter is kept constant from batch 
to batch. (8) Sour cream churns more easily than sweet cream. Peiser 
(1916) has stated that the greater proportion of bacteria in ripened cream 
are removed during churning by the buttermilk. Butter contains about 
one-tenth as many as are in the cream. 
Flavor of Butter. This is dependent upon a large number of factors 
and opinion is still divided with regard to which is the most important. 
That bacteria are important in changing the flavor of butter after it 
has been made is improbable. Conn has attempted to make a distinc- 
tion between “ flavor.” and “ aroma” but such a division is probably 
quite artificial. 
Rancidity is a term which covers a multitude of abnormalities in 
the taste of butter. Guthrie (1917) in his interesting paper has given a 
review of the literature. In his experiments, he attempted to determine 
whether rancidity was due to chemical cow enzyme or biological changes. 
He found that none of these factors were important and believes that 
rancidity as defined by butter judges is rarely found. No marked 
change in the iodine number was caused by high temperatures, ight or 
air. 
