How MLF Works
After primary alcoholic fermentation, lactic acid bacteria (primarily Oenococcus oeni) convert sharp malic acid into milder lactic acid and carbon dioxide. This is not technically a fermentation in the traditional sense, but the name persists.
Effects on Wine
- Reduced acidity — the wine feels rounder and softer
- Buttery notes — diacetyl, a byproduct of MLF, creates the buttery character associated with oaked Chardonnay
- Increased stability — converting malic acid prevents unintended MLF in bottle
When MLF Is Desired
Nearly all red wines undergo MLF to soften their acidity. For whites, it depends on style: full-bodied, oaked Chardonnays typically undergo MLF, while crisp Sauvignon Blancs and Rieslings usually do not, preserving their fresh, zesty character.
Controlling MLF
Winemakers can encourage MLF by maintaining warm cellar temperatures and inoculating with bacteria, or prevent it through chilling, filtration, or sulfite addition.