What is malolactic fermentation?

Picture biting into a green apple versus spooning up some yoghurt — that contrast captures what malolactic fermentation does to wine. Bacteria called *Oenococcus oeni* convert the tart malic acid (green-apple tang) into gentler lactic acid (dairy softness), releasing a tiny bit of CO₂ along the way.

For reds, MLF is essentially non-negotiable. Without it, a Bordeaux or a Barolo would feel aggressively sharp, and the leftover malic acid could trigger an unwanted fizz in the bottle months later. That's why winemakers let it happen right after the main alcoholic fermentation, usually keeping the cellar warm enough — around 18-22 °C — for bacteria to do their work.

Whites are where the real debate lives. Full MLF gives you that creamy, buttery Burgundy Chardonnay character (hello, Meursault). But block it — with a quick dose of sulphur or by chilling the wine — and you keep the bright, racy acidity that makes Chablis or Sancerre so refreshing. Some clever winemakers split the batch: half goes through MLF, half doesn't, and they blend for the best of both worlds.

The buttery flavour specifically comes from diacetyl, a compound produced during the conversion. At low levels (1-4 mg/L) it adds appealing richness. Push it higher and the wine starts tasting like movie-theatre popcorn — a fault most winemakers work hard to avoid through careful temperature control and lees stirring.