tion to exist
between the bacterial content of the wash water and the keeping quality
of the butter. Some creameries have tried filtered water but under
ordinary conditions a filter, unless it is tended to with great
regularity, becomes a source of infection rather than otherwise.

~Changes in germ content.~ The bacteria that are incorporated with the
butter as it first "comes" undergo a slight increase for the first few
days. The duration of this period of increase is dependent largely upon
the condition of the butter. If the buttermilk is well worked out of the
butter, the increase is slight and lasts for a few days only, while the
presence of so nutritious a medium as buttermilk affords conditions much
more favorable for the continued growth of the organisms.

While there may be many varieties in butter when it is fresh, they are
very soon reduced in kind as well as number. The lactic acid group of
organisms disappear quite rapidly; the spore-bearing species remaining
for a somewhat longer time. Butter examined after it is several months
old is often found to be almost free from germs.

In the manufacture of butter there is much that is dependent upon the
mechanical processes of churning, washing, salting and working the
product. These processes do not involve any bacteriological principles
other than those that are incident to cleanliness. The cream, if ripened
properly, will contain such enormous numbers of favorable forms that the
access of the few organisms that are derived from the churn, the air, or
the water in washing will have little effect, unless the conditions are
abnormal.

BACTERIAL DEFECTS IN BUTTER.

~Rancid change in butter.~ Fresh butter has a peculiar aroma that is very
desirable and one that enhances the market price, if it can be retained;
but this delicate flavor is more or less evanescent, soon disappearing,
even in the best makes. While a good butter loses with age some of the
peculiar aroma that it possesses when first made, yet a gilt-edged
product should retain its good keeping qualities for some length of
time. All butters, however, sooner or later undergo a change that
renders them worthless for table use. This change is usually a rancidity
that is observed in all stale products of this class. The cause of this
rancid condition in butter was at first attributed to the formation of
butyric acid, but it is now recognized that other changes also enter
in.[171] Light and especially air