18 STORRS AGRICULTURAL EXPERIMENT STATION. 
parts of the world it is called ‘‘cream souring.’’ It has been 
found that good flavors are especially developed by the acid- 
forming species of bacteria. It has been assumed, therefore, 
that the development of flavor and the development of acid are 
essentially identical, or at least necessarily associated. Some 
practical, as well as scientific, butter-makers are teaching that 
one essential point to be aimed at in the cream ripening is to 
cause the acid-producing organisms to grow rapidly in order to 
develop an acid and flavor before the other organisms have a 
chance to increase. ‘The fact that the extent of the ripening is 
determined by the amount of acidity conveys the impression 
that the ripening and the souring are identical. ‘The idea was 
advanced by myself, however, some years ago, that flavor pro- 
duction is independent of acid production, and while many of 
the acid-producing species also produce changes in the cream 
which give rise to a good flavor, equally good flavors may be 
obtained by species of bacteria that produce no acid, and that 
some species of bacteria may produce acid in abundance with- 
out giving rise to the proper flavor. ‘This conclusion was also 
reached by other bacteriologists. Storch, who first worked - 
with pure bacteria cultures for cream ripening, found some 
species producing acid but not good flavor, and the.same results 
were reached by Weigmann. 
The relation of ripening to the aroma of butter is also an 
uncertain one. ‘There are several pure cultures used in differ- 
ent dairying countries for artificially ripening cream, most of 
which produce favorable results so far as concerns acids and 
flavors, but none of which appears to give a satisfactory aroma. 
Each of these three factors seems to be essential to a proper 
cream ripening, and we cannot hope to satisfactorily control 
this ripening until we know how and under what condition 
flavor, acid, and aroma are produced. Plainly, if we find that 
all three are produced by the same conditions and by the same 
species of bacteria, our method of handling cream for butter- 
making will be determined by this fact; while if we find that 
they are produced by different and independent agencies, the 
method of handling cream must be different. 
The final settlement of these questions can only be reached 
after a long series of experiments. To determine accurately 
the relation of flavor and aroma to bacterial growth it has 
