. F., a temperature that is most favorable
for the growth of the lactic bacteria. Since there is a large number of
bacteria concentrated in a small volume, and the temperature, as
well as all other conditions, is favorable to growth, multiplication
of the bacteria goes on rapidly, and as a consequence, acid is
formed in large amounts, as is shown by the following figures given
by Publow for the manufacture of the export type of cheddar cheese:

Acidity of milk before adding rennet .2 to .21 per cent
Acidity of whey before heating curd .14 to .145 "
Acidity of whey before removing from curd .16 to .18 "
Acidity of whey coming from the curd after
removal of whey and curd is packed .24 to .30 "
Acidity of whey coming from curd before milling .65 to .75 "
Acidity of whey coming from curd before salting .90 to 1.10 "

If the milk had been kept at the same temperature as the curd, the
acidity would have increased much more slowly since the acid would
have been distributed through a larger volume. In the cheese curd
the same amount of acid is probably formed, as would have been
produced in the total amount of milk during the same interval.

The acid produced by this bacterial activity has a most marked
effect on the curd. At first the curd masses are tough and firm,
the particles showing no tendency to adhere to each other. As the
acid increases in amount, the curd becomes plastic, the outer
surface of the particles adhering or "matting," as the maker
expresses it. The result is a solid coalescent mass of curd, which
is cut into small pieces, _i.e._, "milled," before it is put to
press. The acid allows the blending of the pieces under the
influence of the pressure so that a cheese is one single mass. Under
certain abnormal conditions, the development of acid may be
interfered with and the particles of curd fail to mat, in which
case, the cheese will be crumbly when it is cut. The determination
of the proper time for pressing is made by the application of what
is known as the hot iron test. This is made by determining the
length of the "strings" or "threads" which can be drawn from a mass
of curd when it is brought in contact with a hot iron at a cherry
red heat, the length of the curd threads being a measure of the
amount of acid that has been formed in the curd.

The rate of acid formation within the curd particles is also
measur