🍷 Malolactic fermentation

Malolactic fermentation, or "malo", is a second fermentation of wine that is done not by yeast but by bacteria. They turn sharp malic acid into soft lactic acid. The wine becomes softer and rounder.

The work is done by wine lactic acid bacteria, most often the species Oenococcus oeni. They start after the main alcoholic fermentation, while the wine is still warm, or the winemaker adds them to the tank. Malolactic fermentation takes place in most red wines and in some whites, such as Chardonnay.

As a by-product the bacteria create diacetyl. It gives a creamy, buttery smell that is familiar from some barrel-aged Chardonnays. After malolactic fermentation a wine may have more histamine. If a winemaker wants to keep freshness and bright acidity, for example in Riesling, he blocks the process.

The same kind of bacteria work in dairy products. Yogurt, kefir, sour cream and the souring of milk are related processes involving lactic acid. This is why wine can have similar creamy notes.