loped in the curd will
be too high before the curd is sufficiently firm; with a very sweet
milk, the reverse may be true. It is desirable for the cheesemaker
to obtain as good an idea as possible of the condition of the milk
with reference to its bacterial content, since this will determine
the rate at which acid will be formed in the curd. If the milk is
too sweet, _i.e._, too low in acid-forming bacteria, a starter
should be added. The only methods by which this information can be
obtained by the maker is by determining the acidity by the usual
method or better by the use of the rennet test by which is
ascertained the time required for a given amount of rennet to curdle
a definite quantity of milk at a standard temperature. The varying
factor in the test will be the acidity of the milk. Very slight
differences influence profoundly the time of curdling. If, working
under standard conditions, it is found that the time of curdling of
one sample is 10 seconds and of another sample, 20 seconds, it is
proof that the acidity of the first is higher than that of the
second, that its bacterial content is greater and that acidity will
develop in the curd more rapidly. The first may need a small amount
of starter, the second a larger quantity. Working with milk from the
same source, the maker, from his experience, will know how much
starter should be added to milk that has given a certain result with
the rennet test in order that the acid shall be developed in the
curd at a desired rate.

=Ripening of cheese.= The curd at the time it is put to press is tough
and rubbery, and has none of the characteristic flavor of cheddar
cheese; it is also quite insoluble and indigestible. Before the
cheese is fit to eat it must pass through a complex series of
changes which are collectively known as _ripening_. In these changes
there is not only a breaking down of the casein into soluble
compounds, which process makes the cheese soft and plastic under
pressure, but the characteristic flavor is developed in greater or
less degree. A very considerable part of the cheese thus becomes
soluble in water, and it is much more easily digested than in an
unripened condition.

The different factors that are operative in the ripening changes are
not yet fully known, but in recent years as a result of scientific
study, material progress in the study of the changes has been made.

=Rennet.= The commercial rennet extract when in condition for use
contai