This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
Students who have some knowledge of chemistry will see at once that the breaking down of a complex organic substance like sugar into simpler ones as alcohol and carbon dioxide means a loss or waste of energy or working power. Yeast while splitting up the sugar takes to itself or gives off as heat a quantity of the force which was formerly stored in the sugar. Indeed, so much heat is given off during alcoholic fermentation that in breweries large quantities of ice have to be used to cool the fermenting liquid, or it would get so warm that the fermentation would be stopped. So far as man's food is concerned, fermentation that produces alcoholic liquors is pure waste. It destroys sugar, which is a useful food, and gives instead carbon dioxide gas, which is useless to him, and alcohol, which is worse than useless as an article of diet, though having many uses in the arts, as in making varnishes. Sugar is a useful nourishing food; alcohol is a poison which tends to injure nearly all the organs of the body.
Can alcohol be made without the aid of the ferment? How are preserves protected from fermentation? Why is alcoholic fermentation a waste of energy ? Why is it, so far as man's food is concerned, worse than a waste ?
* The technical or generic name of the yeast plant or alcoholic ferment is Saccharomyces. There are several species of this genus: the yeast used by the baker and brewer is Saccharomyces Cerevisiae.
† Small quantities of other substances are also found in alcoholic fermentation, and a small part of the sugar is used as food by the yeast.
Common Yeast, as usually seen, is a thick yellow-brown liquid. Examined with a microscope, this liquid is found to contain myriads of tiny plants belonging to the group of Fungi. These plants are ovoid, and may be single or grouped together. In suitable liquids they multiply with great rapidity by young cells budding off from the older ones. Yeast cells may be dried and yet retain their vitality for a long time, ready to set up alcoholic fermentation whenever they reach a dilute solution of sugar.