What is malolactic fermentation and how does it affect wine?

• A. A primary fermentation converting sugars to alcohol.
• B. A secondary fermentation converting sharp malic acid to softer lactic acid, reducing acidity and adding creamy, buttery or lactic character in some wines.
• C. A filtering process used to remove solids.
• D. A fermentation that increases malic acid.

Answer: (B)

Malolactic fermentation is a secondary fermentation carried out by lactic acid bacteria that converts malic acid into lactic acid and carbon dioxide. This transformation lowers the wine’s sharp acidity, yielding a smoother, rounder mouthfeel. It can also produce diacetyl, which gives buttery, creamy, or lactic flavors that add complexity in some wines. Because malic acid is reduced, the wine becomes less tart and can be more microbiologically stable. It is separate from the primary fermentation (yeast turning sugars into alcohol) and is not a filtering process. It does not increase malic acid; it consumes it. Factors like temperature, pH, SO2 levels, and whether a starter culture is used influence whether it occurs.