A process in which an agent causes an organic substance to break down into simpler substances; especially, the anaerobic breakdown of sugar into alcohol WordNet 3.0 & Open English WordNet

Fermentation is a metabolic process that produces chemical changes in organic substances through the action of enzymes. Wikipedia

Metabolic process whereby electrons released from nutrients are ultimately transferred to molecules obtained from the breakdown of those same nutrients. Wikipedia Disambiguation

Enzymatic conversion of organic compounds Wikidata

Any enzymatic transformation of organic substrates, especially carbohydrates, generally accompanied by the evolution of gas. OmegaWiki

Any of many anaerobic biochemical reactions in which an enzyme (or several enzymes produced by a microorganism) catalyses the conversion of one substance into another; especially the conversion (using yeast) of sugars to alcohol or acetic acid with the evolution of carbon dioxide. Wiktionary

The action of enzymes in breaking down organic substances during fermentation. Wiktionary

A fermentation; hence, an analogous process by which an infectious disease is believed to be developed. Wiktionary