The process of fermentation, which has for its object either the
manufacture of bread, or of an alcoholic product in a more or less
concentrated form, is very similar in action during its earlier stages.
It commences with the growth and multiplication of the fermenting germs
contained in the minute organisms floating in the air, the inorganic
constituents of the water, and the protoplasm (essence of life) of
the yeast; and all the changes brought about are accompanied by heat.
Fermentation is caused by the decomposition of the starch and gluten
of a solution of either potatoes, flour, or malted barley, which
decomposition is accompanied by an evolution of gas. There is also
a peculiar vibration given to the various bodies in contact, which
agitates the whole. This agitation is increased by the bursting of the
starch-cells and the formation therefrom of maltose, and also by the
changing of the maltose sugar into carbonic acid gas. Substances in a
state of decomposition are capable of bringing about a change in the
chemical composition of bodies with which they are in contact. Most
of the vegetable substances used in fermentation have a constituent
part--sugar, starch, or some other substance--which is easily converted
into a fermentable sugar by the action of yeast, or of diluted mineral
acids, or by a constituent of malted barley, called diastase. The sugar
produced by these means is resolved into carbonic acid gas and alcohol
by vinous fermentation. It will be seen, therefore, that fermentation
is started by the saccharine element in the ferment, which is termed
maltose; the process is then kept up by the gluten, which, becoming
decomposed, aids the sugar and starch in the work of providing food
for the yeast as soon as the latter is brought in contact with it. The
fermentation then takes place very rapidly, and carbonic acid gas is
generated and given off in proportion to the amount of the products
contained in the ferment, or sponge, and also to the strength and
freshness of the yeast: especially is this so with gluten, which is the
great agent of fermentation, when in a state of decomposition and when
in contact with yeast.