ed and cleaned; the sour whey thus presents
favorable conditions for the growth of the lactose-fermenting
yeasts. The return of the whey to the farm in the milk can that is
often imperfectly cleaned may serve to contaminate the milk with the
yeast. In the making of Swiss cheese the whey is often so handled as
to favor especially the growth of such yeasts, and since this type
of cheese is prepared from sweet milk, the competition between the
yeast and the acid-forming bacteria is not so sharp as in the making
of cheddar cheese. The writers have found several instances where
considerable loss was occasioned in the Swiss cheese industry
through the development of gassy cheese due to this type of
fermentation.

The yeasty or alcoholic fermentation may also be of importance in
butter making. In many sections of the country the milk is separated
on the farm and the cream is forwarded to the creamery at more or
less infrequent intervals. It becomes sour and if it has become
contaminated with yeasts, they will find favorable conditions for
growth in the acid medium. A large amount of carbon dioxide gas is
produced. Cans of gathered cream often foam to such an extent as to
run over, and in some cases actual explosions have occurred on
account of the great pressure caused by the gas.

=Bitter fermentation of milk.= Bitterness in milk may be due to
bacteria that enter the milk after it is drawn from the cow, or it
may be caused by the feed consumed by the animal. It has been
previously shown that certain specific substances contained in the
food may be absorbed and reappear in the milk. If the animal eats
ragweed, lupines, or other plants containing bitter substances, the
milk is likely to have a bitter taste, which will be noticeable at
the time the milk is drawn. The milk of cows at certain advanced
stages of lactation may show a bitter taste, due to a change in the
ash constituents of the milk in which the lime salts are largely
replaced by salts of sodium.

There are many bacteria that will impart to milk a bitter taste.
Milk that has undergone the sweet-curdling fermentation is likely to
be bitter, as is the ease with pasteurized milk. Some of the
acid-forming bacteria are able to develop a bitter principle, the
milk retaining a pleasant odor and having the normal amount of acid,
while the taste is intensely bitter. One of the authors (H) found in
the case of a Wisconsin brick cheese factory, that the usual acid
organism