Secondary fermentation

Secondary fermentation meaning in wine

In formal OIV usage, secondary fermentation is alcoholic fermentation in a hermetically sealed bottle or pressure-resistant tank. The carbon dioxide produced remains under pressure and creates a sparkling wine’s effervescence. In the traditional method this fermentation occurs in the bottle; closed-tank methods conduct it in a pressure-resistant tank. Malolactic fermentation (MLF) is a separate bacterial conversion of malic acid into lactic acid and carbon dioxide. Australian wine sources sometimes call MLF “secondary fermentation,” but naming the process explicitly avoids confusion. Racking an incompletely fermented still wine into another vessel does not by itself create a separate fermentation; alcoholic fermentation is simply continuing in a new vessel.

Sources: OIV definition of secondary fermentation; Australian Wine Research Institute fermentation resources.