This section is from the book "A Treatise On Flour, Yeast, Fermentation And Baking Together With RecipesFor Bread And Cakes", by Julius Emil Wihlfahrt. Also available from Amazon: A treatise on flour, yeast, fermentation and baking, together with recipes for bread and cakes.
The term fermentation was first applied to the action of yeast changing the sugars or carbohydrates contained in the dough into alcohol and carbon dioxide gas.
The different stages of fermentation are known as alcoholic, acetous and putrefactive fermentations.
The process of fermentation, which has for its object the manufacture of bread, must be of alcoholic nature.
Alcoholic fermentation is the one that makes the bread light and porous.
Acetous fermentation, when present in the right percentage, improves the flavor of the bread, but as soon as it becomes too strong it will cause the alcoholic fermentation to stop, and the result is a heavy loaf of bread.
The putrefactive fermentation is the last stage of fermentation following the acetous fermentation. Sometimes it is present in dough and causes the much-dreaded "rope in bread."
Alcoholic fermentation is the name given to the change which takes place in the maltos matter of the dough, forming carbonic acid gas, which, if the bread is baked at the right time, will lighten the bread and make it digestible.
Acetous fermentation, when present in the right percentage, softens the gluten and increases the expansion qualities of the dough. A remarkable fact about ferments is that the substances they produce, in time, put a stop to their own activity.
Fermentation, then, is the name given to the process, in which soluble ferments or enzymes play an important part, by which the carbohydrates, especially the sugars, are decomposed mainly into carbon dioxide and alcohol, with traces of acids and other substances.