ric., 1904.

CHAPTER VIII.

BACTERIA IN CHEESE.

The art of cheese-making, like all other phases of dairying, has been
developed mainly as a result of empirical methods. Within the last
decade or so, the subject has received more attention from the
scientific point of view and the underlying causes determined to some
extent. Since the subject has been investigated from the bacteriological
point of view, much light has been thrown on the cause of many changes
that were heretofore inexplicable. Our knowledge, as yet, is quite
meager, but enough has already been determined to indicate that the
whole industry is largely based on the phenomena of ferment action, and
that the application of bacteriological principles and ideas is sure to
yield more than ordinary results, in explaining, in a rational way, the
reasons underlying many of the processes to be observed in this
industry.

The problem of good milk is a vital one in any phase of dairy activity,
but it is pre-eminently so in cheese-making, for the ability to make a
first-class product depends to a large extent on the quality of the raw
material. Cheese contains so large a proportion of nitrogenous
constituents that it is admirably suited, as a food medium, to the
development of bacteria; much better, in fact, than butter.

INFLUENCE OF BACTERIA IN NORMAL CHEESE PROCESSES.

In the manufacture of cheddar cheese bacteria exert a marked influence
in the initial stages of the process. To produce the proper texture that
characterizes cheddar cheese, it is necessary to develop a certain
amount of acid which acts upon the casein. This acidity is measured by
the development of the lactic-acid bacteria that normally abound in the
milk; or, as the cheese-maker expresses it, the milk is "ripened" to the
proper point. The action of the rennet, which is added to precipitate
the casein of the milk, is markedly affected by the amount of acid
present, as well as the temperature. Hence it is desirable to have a
standard amount of acidity as well as a standard temperature for
coagulation, so as to unify conditions. It frequently happens that the
milk is abnormal with reference to its bacterial content, on account of
the absence of the proper lactic bacteria, or the presence of forms
capable of producing fermentative changes of an undesirable character.
In such cases the maker attempts to overcome the effect of the unwelcome
bacteria by adding a "starter;" or he must vary