When It Happens
All red wine. Some white. Never sparkling base. Red wine almost universally goes through MLF — without it, reds taste sharp and aggressive. The bacteria need warmth (around 18–20°C) and time, so MLF usually happens right after the main fermentation, in the barrel or tank.
For white wine, it's a choice. Chardonnay is the famous example: Burgundy-style (MLF, barrel, buttery) vs Chablis-style (no MLF, steel, sharp). Both are “right.” Just different. Most Argentine Chardonnay goes through partial MLF — buttery but not heavy.
Sparkling wines almost never undergo MLF in the base wine — they need the high acidity to feel bright and fresh against the bubbles. Most fresh aromatic whites (Riesling, Torrontés, Sauvignon Blanc) also skip MLF for the same reason.