
BACTERIA IN THE DAIRY. : 45 
Having thus obtained a number of species of bacteria, between 
thirty and forty in all, the experiments with ripening cream 
were performed as follows:* Four quarts of milk were obtained 
daily from a milk dealer and the milk was passed through the 
centrifugal machine. ‘The cream obtained each day was about 
one pint. It was divided at once into two lots of half a pint 
each and each lot placed in a sterilized fruit can. y,The cream 
was now put into a pail of water and the water heated by steam 
until the temperature of the cream reached 69° or 70°C. (158°F.) 
This temperature was continued for five or ten minutes and then 
the cream, closed from the air, was set aside to cool, or cooled 
under the water tap. After cooling it was ready for inoculation 
and ripening. 
In heating the cream up to the temperature of 70°C. (158°F.) as 
above explained, it was not expected that the cream was sterilized. 
On the contrary it is well known from many experiments, that such 
a temperature leaves many bacteria in the cream, especially in 
the form of spores. Nevertheless, this method, which is gener- 
ally known as pasteurization, does so reduce the number of 
bacteria that it was thought to be satisfactory for purposes of our 
experiment. There would be left in the milk some spores which 
would germinate somewhat slowly, but only a small number of 
active bacteria would be present. It was assumed that if to such 
cream a sufficient quantity of the bacteria of experiment was 
added in culture, these bacteria being present in such quantities 
in the cream, would grow rapidly and produce their own effect 
upon the cream, independent, or nearly independent, of the nor- 
mal species that chanced to remain after the sterilization. It is, 
of course, understood that the experiment would be more rigidly 
correct if the cream could have been sterilized. That, however, 
was an impossibility, because sterilization, requiring a tempera- 
ture of at least 100°, also produces in the cream the taste of 
boiled milk, and that taste is carried over into the butter and 
produces a flavor in the butter entirely foreign to normal butter. 
In one or two experiments of this sort that were performed, the 
taste of the boiled milk was so much more prominent than any 
other flavor, that the influence of the bacteria of the experiment 
was entirely obliterated (see experiment 74). The only other 
method of absolutely sterilizing the cream would have been to 
* 

* These experiments were carried out by Mr. William M. Esten, who also had charge of the 
exhibit at the Columbian Exposition. 
