ion
of certain decomposition products formed by various bacteria. Aroma is a
quality often confounded with flavor, but this is produced by volatile
products only, which appeal to the sense of smell rather than taste.
Generally a good flavor is accompanied by a desirable aroma, but the
origin of the two qualities is not necessarily dependent on the same
organisms. The quality of flavor and aroma in butter is, of course, also
affected by other conditions, as, for instance, the presence or absence
of salt, as well as the inherent qualities of the milk, that are
controlled, to some extent at least, by the character of the feed which
is consumed by the animal. The exact source of these desirable but
evanescent qualities in butter is not yet satisfactorily determined.
According to Storch,[157] flavors are produced by the decomposition of
the milk sugar and the absorption of the volatile flavors by the butter
fat. Conn[158] holds that the nitrogenous elements in cream serve as
food for bacteria, and in the decomposition of which the desired
aromatic substance is produced. The change is unquestionably a complex
one, and cannot be explained as a single fermentation.

There is no longer much doubt but that both acid-forming and
casein-digesting species can take part in the production of proper
flavors as well as desirable aromas. The researches of Conn,[159] who
has studied this question most exhaustively, indicate that both of these
types of decomposition participate in the production of flavor and
aroma. He has shown that both flavor and aroma production are
independent of acid; that many good flavor-producing forms belong to
that class which renders milk alkaline, or do not change the reaction at
all. Some of these species liquefied gelatin and would therefore belong
to the casein-dissolving class. Those species that produced bad flavors
are also included in both fermentative types. Conn has found a number of
organisms that are favorable flavor-producers; in fact they were much
more numerous than desirable aroma-yielding species. None of the
favorable aroma forms according to his investigations were lactic-acid
species,--a view which is also shared by Weigmann.[160]

McDonnell[161] has found that the production of aroma in certain cases
varies at different temperatures, the most pronounced being evolved near
the optimum growing temperature, which, as a general rule, is too high
for cream ripening.

The majority of bacteria