Yeast

Yeast (primarily Saccharomyces cerevisiae) is the engine of winemaking. During fermentation, yeast cells consume glucose and fructose in grape juice and produce ethanol, CO₂, heat, and a complex array of flavour compounds including esters, higher alcohols, and fatty acids.

Winemakers choose between commercial (cultured) yeast strains and wild (indigenous/ambient) yeast. Commercial yeasts are selected for predictability, reliability, and specific flavour profiles — some strains enhance tropical fruit in Sauvignon Blanc; others build structure in Syrah. Wild yeasts, naturally present on grape skins and in the winery, are favoured by many natural wine producers for their complexity and terroir expression, but carry a higher risk of stuck fermentation or off-flavours.

Fermentation temperature is critical: cool fermentation (12–16°C for whites) preserves delicate aromatics; warm fermentation (25–32°C for reds) extracts more colour and tannin and encourages complex flavour development.

Yeast also plays a second role in traditional-method sparkling wine, where a second yeast inoculation drives secondary fermentation in the bottle or tank, building pressure and eventually autolysing to provide toasty, biscuit complexity.