a. If the
rennet thus prepared contains no harmful bacteria and the milk is of
good quality, the cheese is likely to ripen in a normal manner. The
rennet should be prepared with due regard to bacteriological
principles, a condition that is rarely met in Swiss factories in
this country.

Swiss cheese has two striking characteristics, the flavor and the
presence of holes or "eyes." The flavor is sweetish rather than the
sharp and pungent flavor of cheddar cheese. The bacteria concerned
in its production are not known, but it is certain that specific
organisms play some role, since if the flora of the cheese is
changed by salting the curd or by the use of milk containing large
numbers of lactic bacteria, the flavor will also be changed. This
role of the acid-forming bacteria in Swiss is the same as in
cheddar, _i.e._, through the acid, conditions are established for
peptic action, the curd being partially digested while at the same
time the curd mass is protected from putrefactive processes.

In Swiss cheese during the ripening process, holes about the size of
a large cherry develop which should be quite uniformly distributed
throughout the cheese. The inner surface of the hole is glistening
and, in a well-ripened cheese, a small quantity of clear brine,
_i.e._, "tears" may be noted. These holes or "eyes" may be called
the trade mark of the Swiss cheese, since without them the product
has a lessened commercial value, even if it possesses the typical
flavor. The "eyes" are caused by bacteria that ferment the lactic
acid produced by the lactic bacteria, forming from it propionic
acid and carbon dioxide, the latter gas being the cause of the hole
or "eye."

[Illustration: Fig. 38.--Swiss Cheese.

Normal development of "eyes" in a Swiss cheese. The eyes are
generally as large as a cherry.]

The "eye"-forming organisms cannot grow in the presence of any
amount of salt, hence, if salt is added directly to the curd, the
cheese is likely to be "blind" or free from holes. The eyes are
formed not at the time gas holes are produced in a cheddar cheese,
_i.e._, early in the ripening process, but after a lapse of three or
four weeks. They are most abundant in the middle of the cheese since
the manner of salting is such as to inhibit their formation near the
surface. The eye-forming bacteria may have some effect on the flavor
of the cheese.

The Swiss maker encounters the same troubles as does the cheddar
maker. Gassy cheese i