cheese-making, then practically all abnormal
conditions could be controlled by the use of properly selected starters.
Numerous attempts have been made to perfect this system with reference
to cheddar cheese, but so far they have been attended with imperfect
success. The reason for this is that in pasteurizing milk, the soluble
lime salts are precipitated by the action of heat, and under these
conditions rennet extract does not curdle the casein in a normal manner.
This condition can be restored, in part at least, by the addition of
soluble lime salts, such as calcium chlorid; but in our experience,
desirable results were not obtained where heated milks to which this
calcium solution had been added were made into cheddar cheese.
Considerable experience has been gained in the use of heated milks in
the manufacture of certain types of foreign cheese. Klein[182] finds
that Brick cheese can be successfully made even where the milk is heated
as high as 185 deg. F. An increased weight is secured by the addition of
the coagulated albumin and also increased moisture.

~Bacteria in rennet.~ In the use of natural rennets, such as are
frequently employed in the making of Swiss cheese, considerable numbers
of bacteria are added to the milk. Although these rennets are preserved
in salt, alcohol or boric acid, they are never free from bacteria.
Adametz[183] found ten different species and from 640,000 to 900,000
bacteria per cc. in natural rennets. Freudenreich has shown that rennet
extract solutions can be used in Swiss cheese-making quite as well as
natural rennets; but to secure the best results, a small quantity of
pure lactic ferment must be added to simulate the conditions that
prevail when natural rennets are soaked in whey, which, it must be
remembered, is a fluid rich in bacterial life.

Where rennet extract or tablets are used, as is generally the case in
cheddar making, the number of bacteria added is so infinitesimal as to
be negligible.

~Development of acid.~ In the manufacture of cheddar cheese, the
development of acid exerts an important influence on the character of
the product. This is brought about by holding the curds at temperatures
favorable to the growth of the bacteria in the same. Under these
conditions the lactic-acid organisms, which usually predominate, develop
very rapidly, producing thereby considerable quantities of acid which
change materially the texture of the curds. The lactic acid acts upon
the c