THE RIPENING OF CREAM. “5 
least to the American market. In general it may be stated 
that the cultures used produce a good quality of butter, but 
one with an extremely mild flavor and aroma. Such butter 
does not possess the character of the best type of butter ripened 
by natural conditions. It has been believed that the reason 
for this is that the normal butter flavors are not produced by 
any one type of bacteria, and that consequently the taste of 
butter ripened under natural conditions and, therefore, under 
the influence of a considerable variety of bacteria, is better 
than that produced under the infiuence of a pure culture which 
is a single species. This has been, however, up to the present 
time wholly a matter of theory, for no one has studied the 
ripening of cream under zovmal conditions sufficiently to know 
whether or not there is a multiplication of a large number of 
types of bacteria, or whether in reality the ripening is pro- 
duced by a single species. If this question can be settled, 
manifestly it will contribute largely toward enabling bacteriolo- 
gists to improve the types of cultures which can be used for 
artificial cream ripening. 
METHOD OF EXPERIMENT. 
_ The experiments upon which this paper is based were per- 
formed upon cream obtained from two creameries and four 
private dairies. Each creamery experiment was performed as 
follows: A visit to the creamery was made at such time as 
made it possible to obtain a sample of the cream freshly brought 
into the creamery, and, therefore, just before it is set for 
ripening. The cream sample was put upon ice, was at once 
carried to the laboratory, and was plated as soon as possible, 
always within two hours of the time of collection. Before it 
was plated the cream was diluted commonly with 100,000 
to 250,000 parts of sterilized water, though with very fresh 
cream smaller dilutions were used. These dilutions, of course, 
were very large and introduced certain errors, but they were 
found necessary to make possible a satisfactory determination 
of the number of bacteria on the plates. Upon the next day 
a second visit was made to the creamery and a sample of the 
same cream ripened was obtained just before the time of churn- 
ing. This was in a similar way placed upon ice, brought to 
the laboratory and plated. In this way two series of plates 
