Grape juice mixed with millet ferments quickly and strongly, and the
Romans learned to use this mixture for bread raising, kneading a very
small amount of it through the dough.
215. The Cause of Fermentation. Although alcoholic fermentation, and
the fermentation which goes on in raising dough, were known and
utilized for many years, the cause of the phenomenon was a sealed book
until the nineteenth century. About that time it was discovered,
through the use of the microscope, that fermenting liquids contain an
army of minute plant organisms which not only live there, but which
actually grow and multiply within the liquid. For growth and
multiplication, food is necessary, and this the tiny plants get in
abundance from the fruit juices; they feed upon the sugary matter and
as they feed, they ferment it, changing it into carbon dioxide and
alcohol. The carbon dioxide, in the form of small bubbles, passes off
from the fermenting mass, while the alcohol remains in the liquid,
giving the stimulating effect desired by imbibers of alcoholic drinks.
The unknown strange organisms were called yeast, and they were the
starting point of the yeast cakes and yeast brews manufactured to-day
on a large scale, not only for bread making but for the commercial
production of beer, ale, porter, and other intoxicating drinks.
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