The Biochemistry of Ethanol Fermentation
Enzymatic Pathways from Glucose to Ethanol
At the core of all Alcoholic Spirits is the biological process of fermentation. This document explores the anaerobic transformation of six-carbon sugars (glucose and fructose) by the yeast Saccharomyces cerevisiae. Through the Embden-Meyerhof-Parnas (glycolysis) pathway, a single glucose molecule is broken down into two molecules of pyruvate.
In the absence of oxygen, the yeast performs two subsequent steps: the decarboxylation of pyruvate into acetaldehyde (releasing $CO_2$) and the reduction of acetaldehyde into ethanol via the enzyme alcohol dehydrogenase. This document also details the production of secondary metabolites—such as higher alcohols (fusel oils), esters, and organic acids—which serve as the "flavor precursors" that will be concentrated during the distillation phase.