Fermentation Basics

Fermentation is the biological engine of every alcoholic drink. In simple terms: yeast eats sugar and produces ethanol + CO₂ + flavor.

Yeast (usually *Saccharomyces cerevisiae*) is a single-celled fungus. Given warmth, moisture, and sugar, it multiplies rapidly and metabolizes the sugar without oxygen. The byproducts are ethanol, carbon dioxide, and a small orchestra of aromatic compounds (esters, higher alcohols, fatty acids) that give beer, wine, and the base wash of every spirit its character.

Different drinks start with different sugars:

• Grains (barley, corn, rye, wheat) → whisky, beer, vodka, gin base.
• Grapes and fruit → wine, brandy.
• Sugarcane / molasses → rum.
• Agave → tequila, mezcal.

Grains do not contain free sugar; their starch must be converted to sugar first, either by malting (letting the grain sprout so it makes its own enzymes) or by adding enzymes.

Normal brewers’ yeast tolerates roughly 12–16% ABV before the alcohol becomes toxic to the yeast itself and fermentation stalls. That is why wine and beer sit in that range naturally, and why we need distillation to reach the strengths of spirits.