Jälkikäyminen

Jälkikäyminen, also known as secondary fermentation or conditioning, is a stage in the production of certain alcoholic beverages, most notably beer and wine, that occurs after the primary fermentation is complete. During primary fermentation, yeast consumes most of the available sugars and produces alcohol and carbon dioxide. Jälkikäyminen is a slower process where remaining sugars are converted, and other desirable or undesirable compounds may develop.

In beer making, jälkikäyminen can occur in a secondary fermenter, a conditioning tank, or even within the bottle or keg. This stage allows the beer to clarify as yeast and other particles settle out. It also contributes to the flavor profile by allowing esters and other flavor compounds to mature. Some beers, especially those intended for aging or with higher alcohol content, benefit significantly from a longer jälkikäyminen period. Carbonation can also develop during this stage, either through the slow release of residual CO2 from fermentation or by the addition of priming sugar.

In winemaking, jälkikäyminen is often referred to as malolactic fermentation (MLF) if it involves the conversion of malic acid to lactic acid by lactic acid bacteria. This process softens the acidity of the wine, adds complexity, and can contribute buttery or nutty aromas. While MLF is common in red wines and some white wines, it is actively prevented in others where a crisp acidity is desired. Similar to beer, wine can also undergo a period of aging after MLF, allowing flavors to meld and develop further.