eable
taste. In cheese the gases cause the formation of holes, more or
less numerous, depending on the number of the gas-forming bacteria
in the milk. Where these bacteria are abundant, gas may appear while
the curd is in the vat, causing it to float in the whey, when it is
known as a "floater." Again, the gas may not become evident until
the cheese is in the press or on the curing shelf, when it becomes
apparent by the swelling or bulging of the cheese. Such cheese is
termed "huffed" or "swelled." The internal pressure may be so great
as to cause the cheese to crack and to force out some of the curd.
The presence of gas holes is indicative of a poor cheese, because
the formation of gas is always accompanied by the presence of other
undesirable compounds.

Pure culture starters are often used to overcome gassy
fermentations. In cheese a certain amount of acid can be produced by
the acid-forming bacteria. When the pure lactic bacteria alone are
present, the cheese is very likely to be of good quality. If the
sugar is fermented by gas-forming organisms, the curd will be full
of holes and the flavor poor, while if the sugar is fermented by a
mixture of the desirable and undesirable bacteria, the quality of
the product will depend on the relation of the two types. If through
the addition of a pure-culture starter, the proportion of desirable
bacteria is increased, the gas will be lessened in amount and the
cheese improved. It was formerly supposed that the lactic bacteria
had an injurious effect on the gas-forming organisms. There is no
good reason to believe that this is the case, but that both grow in
the milk and cheese, but since only a certain amount of acid can be
produced, it is important to have as much of it formed by the lactic
bacteria as possible, since the amount of injurious products in the
cheese will thus be limited.

[Illustration: Fig. 37.--Gassy Cheese.

Such a cheese is worthless on account of its poor flavor. The
irregular holes are mechanical. The crack on the upper side is due
to the pressure of the gas which has caused the cheese to bulge at
this point.]

The gas formed in the curd before the cheese is put to press can be
gotten rid of by proper manipulation of the curd. While this
treatment may improve the appearance of the cheese, it does not
eliminate the substances that impart to the cheese undesirable
qualities.

Gassy curds have also been treated by washing the curd with cold
water. Ca