temperatures, say above 65 deg. F.

~"Gassy" fermentations in cheese.~ One of the worst and at the same time
most common troubles in cheese-making is where the cheese undergoes a
fermentation marked by the evolution of gas. The presence of gas is
recognized by the appearance either of spherical or lens-shaped holes of
various sizes in the green cheese; often they appear in the curd before
it is put to press. Usually in this condition the curds look as if they
had been punctured with a pin, and are known as "pin holey" curds. Where
the gas holes are larger, they are known as "Swiss holes" from their
resemblance to the normal holes in the Swiss product. If the development
of gas is abundant, these holes are restricted in size. Often the
formation of gas may be so intense as to cause the curds to float on the
surface of the whey before they are removed. Such curds are known as
"floaters" or "bloaters."

If "gassy" curds are put to press, the abnormal fermentation may
continue. The further production of gas causes the green cheese to
"huff" or swell, until it may be considerably distorted as in Fig. 33.
In such cases the texture of the cheese is greatly injured, and the
flavor is generally impaired.

[Illustration: FIG. 33. Cheese made from gassy milk.]

Such abnormal changes may occur at any season of the year, but the
trouble is most common in summer, especially in the latter part.

This defect is less likely to occur in cheese that is well cheddared
than in sweet curd cheese. When acidity is produced, these gassy
fermentations are checked, and in good cheddar the body is so close and
firm as not readily to permit of gaseous changes.

In Swiss cheese, which is essentially a sweet curd cheese, these
fermentations are very troublesome. Where large holes are formed in
abundance (blaehen), the trouble reaches its maximum. If the gas holes
are very numerous and therefore small it is called a "nissler."
Sometimes the normal "eyes" are even wanting when it is said to be
"blind" or a "glaesler."

[Illustration: FIG. 34. Block Swiss cheese showing "gassy"
fermentation.]

One method of procedure which is likely to cause trouble in Swiss
factories is often produced by the use of sour, fermented whey in which
to soak the natural rennets. Freudenreich and Steinegger[209] have shown
that a much more uniform quality of cheese can be made with rennet
extract if it is prepared with a starter made from a pure lactic
ferment.