Malolactic Fermentation
A secondary bacterial process in winemaking that converts sharp malic acid into softer lactic acid, reducing perceived acidity and adding a creamy, buttery texture.
In depth
Malolactic fermentation (MLF) is carried out by lactic acid bacteria, most commonly Oenococcus oeni. It occurs after primary (alcoholic) fermentation, either naturally or through inoculation. The conversion of malic acid — which tastes sharp and green-apple-like — into lactic acid — which tastes softer and milky — noticeably changes the wine's texture and flavour profile.
A by-product called diacetyl is produced during MLF, which is responsible for the classic "buttery" aroma in some Chardonnays. The extent of the buttery note depends on how much diacetyl is produced and whether it is later reabsorbed by the bacteria.
MLF is almost universal in red wine production — it softens the tannins and adds stability. For white wines, the decision to use MLF is stylistic. Unoaked, high-acid whites like Chablis and Muscadet typically avoid MLF to preserve freshness. Fuller, barrel-aged whites like Meursault typically undergo full MLF for a richer, creamier style.
At Level 3, candidates are expected to explain why a winemaker might choose to allow or prevent MLF and link that decision to the intended wine style.
Related exam topics
Frequently asked questions
- Does all wine go through malolactic fermentation?
- Almost all red wines undergo MLF — it reduces harsh acidity and adds softness. For white wines it is a choice: rich barrel-aged whites (like Meursault) typically use it for a creamy texture, while light aromatic whites (like Chablis or Riesling) usually avoid it to preserve fresh acidity.
- How can you tell if a wine has gone through MLF?
- Wines that have undergone MLF tend to have a rounder, creamier mouthfeel with lower perceived acidity. A buttery or creamy aroma on the nose is a strong indicator. In contrast, wines without MLF taste crisper and more tart. In a tasting exam, noting "creamy texture suggesting MLF" is a valid and expected observation.
Practise questions on this topic
Use Vinlecta to practise exam-style questions that test your knowledge of malolactic fermentation and related topics.