Alcoholic fermentation is the biological process in which yeast converts fermentable sugars, mainly glucose and fructose, into ethanol and carbon dioxide. It is the central transformation in winemaking that turns grape must into wine. The process also generates heat and a range of compounds that influence aroma, flavour and texture.
Yeast consumes sugar and produces ethanol, carbon dioxide and energy. It also forms secondary metabolites such as esters, higher alcohols and organic acids, which can contribute fruit, floral, solvent-like or other aromas depending on the strain and conditions. Fermentation continues until the sugar is depleted, the yeast is inhibited or the winemaker deliberately stops the process.
White wines are commonly fermented after pressing, with the juice separated from the skins. Red wines are usually fermented with skins and sometimes seeds or stems to extract colour, tannin and flavour. Temperature and cap management are adjusted to suit the grape and intended style; there is no single universal temperature range for all wines.
Example: yeast ferments grape must into wine, producing ethanol and carbon dioxide. A red Cabernet Sauvignon is commonly fermented with its skins, while a white Sauvignon Blanc is usually fermented as clarified juice.
Alcoholic fermentation converts sugar into ethanol and carbon dioxide through yeast activity. Malolactic fermentation converts malic acid into lactic acid through lactic acid bacteria. The processes are distinct and may occur sequentially or, in some cases, overlap.
Chef’s note: fermentation is not simply the production of alcohol; yeast metabolism also shapes the wine’s aroma and flavour.
This term is one of hundreds covered in depth across OCS courses, learning paths, and 1-on-1 coaching with Chef Eric.
