1 86 BACTERIA IN BUTTER AND OLEOMARGARINE. 
Duration of Ripening. The butter-maker can stop the 
ripening at any point, for, after the cream is churned into butter, 
the bacteria growth ceases. The necessary duration of the ripen- 
ing will vary, however, with the conditions. Sometimes cream, 
when brought to a creamery, is already sour and has, therefore, 
become ripened even before the butter-maker receives it. In other 
cases, especially in winter, it will not only be sweet, but will contain 
small numbers of bacteria and require a much longer ripening. 
Moreover, milk produced under good dairy conditions, clean and 
fairly free from bacteria, will ordinarily require longer ripening than 
milk produced under less favoiable conditions and containing al- 
ready great numbers of bacteria. The length of time will vary 
also with the temperature, being, of course, longer at lower tempera- 
tures. To determine when the cream is sufficiently ripened, "the 
butter-maker has two methods. One is the general appearance to 
his eye and taste, and the other is the degree of acidity. The latter 
factor is determined by the methods described on page 309, and 
the ripening is generally continued until the acidity is 0.5 to 0/65 
per cent. 
THE USE OF STARTERS. 
By far the most important change in the methods of cream- 
ripening is in the wide and almost universal introduction of starters. 
Twenty-five years ago it was sometimes customary to add a starter 
to cream in cold weather simply for the purpose of starting the 
ripening; but to-day almost all good creameries use starters, not so 
much for starting, as for regulating the ripening. 
Prof. Storch, of Copenhagen, first conceived the possibility 
of furnishing to butter-makers cultures of the proper species of 
bacteria, which they might add to their cream for the purpose of 
ripening, somewhat as yeast is used in brewing. This experimenter 
not only conceived the method, but put it into practical operation 
in Denmark. His method consisted i. in pasteurizing the cream 
at about 165 F., for the purpose of destroying most of the bacteria 
that might be present, and 2. in adding to it a pure culture of 
bacteria, whose value in producing a good flavor had been deter- 
