e souring of milk, in putrefying meat, in rotting fruit, or
in decomposing fruit juice, is essentially one of fermentation,
caused by these minute forms of plant life. There are many kinds of
fermentation, each with its own special form of minute plant life or
micro-organism.

In this section we are more especially concerned about that fermentation
which results from the decomposition of sweet fruit, plant, or other
vegetable, juices which are composed largely of water containing sugar and
flavoring matters.

This special form of fermentation is known as alcoholic or vinous
fermentation, and the micro-organisms that cause it are familiarly termed
alcoholic ferments. The botanist classes them as _Saccharomycetes_, of
which there are several varieties. Germs of _Saccharomycetes_ are found on
the surfaces and stems of fruit as it is ripening. While the fruit remains
whole these germs have no power to invade the juice, and even when the
skins are broken the conditions are less favorable for their work than for
that of the moulds,[18] which are the cause of the rotting of fruit.

But when fruit is crushed and its juice pressed out, the
_Saccharomycetes_ are carried into it where they cannot get the oxygen
they need from the air. They are then able to obtain oxygen by taking it
from the sugar of the juice. By so doing they cause a breaking up of the
sugar and a rearrangement of its elements. Two new substances are formed
in this decomposition of sugar, viz., carbon dioxid, which arises
from the liquid in tiny bubbles, and alcohol, a poison which
remains in the fermenting fluid.

Now we must remember that fermentation entirely changes the nature of the
substance fermented. For all forms of decomposition this one law holds
good. Before alcoholic fermentation, the fruit juice was wholesome and
beneficial; after fermentation, it becomes, by the action of the minute
germs, a poisonous liquid known as alcohol, and which forms an essential
part of all intoxicating beverages.

Taking advantage of this great law of fermentation which dominates the
realm of nature, man has devised means to manufacture various alcoholic
beverages from a great variety of plant structures, as ripe grapes, pears,
apples, and other fruits, cane juices, corn, the malt of barley, rye,
wheat, and other cereals.

The process differs according to the substance used and the manner in
which it is treated, but the ultimate outcome is always the same,
viz., t