The most common mix-up in basic oenology
They share the word "fermentation" and happen in the same winery, sometimes in the same tank — but they're chemically distinct processes, with different microorganisms, different inputs, and different outcomes. And no, not every wine goes through both.
Alcoholic fermentation: the one that turns grapes into wine
Done by yeast (mainly Saccharomyces cerevisiae), which consumes the grape's sugar (glucose and fructose) and converts it into ethanol and carbon dioxide. This is the process that literally turns grape must into wine — every wine in the world goes through it, no exceptions. It takes 5 to 15 days, at temperatures between 12°C and 30°C depending on the style being made.
Malolactic fermentation: the one that softens acidity
Done by lactic acid bacteria (mostly Oenococcus oeni), which convert the wine's malic acid — the same sharp acid found in a green apple — into softer lactic acid, the kind found in milk. Unlike the alcoholic fermentation, this one is optional: the winemaker decides whether to let it happen or block it. When it does happen, it's usually weeks or months after the alcoholic fermentation, often in barrel.
Side by side
- Alcoholic: yeast · sugar → alcohol + CO₂ · mandatory · 5-15 days
- Malolactic: bacteria · malic acid → lactic acid + CO₂ · optional · weeks to months
Why not every wine goes through malolactic
It works well in reds, where it softens the tannic grip and rounds out the palate. It also works in some full-bodied whites, like many Chardonnays, where it adds buttery notes. But in aromatic whites like Sauvignon Blanc or Riesling, winemakers usually block it on purpose — that sharp acidity is exactly what gives the wine its freshness, and losing it would mean losing the style.
How to spot a wine that went through malolactic: buttery or creamy notes, a rounder texture, less sharp acidity on the palate. It's a big part of what gives many California Chardonnays their rich, silky character.
How this looks in LagarLab
In the simulator, malolactic fermentation is a real decision you make on your tank, not a fact from a textbook: turning it on changes the pH and acid profile of the wine you're making, just like in a real winery.
What if you decided, with real data?
In LagarLab you control whether your wine goes through malolactic fermentation, and see exactly how the final result changes.
Vinify for free: Agrelo (red)No sign-up. Prefer a white? Try Chablis.
Frequently asked questions
What's the core difference between alcoholic and malolactic fermentation?
Alcoholic fermentation is done by yeasts, mainly Saccharomyces cerevisiae, and converts sugar into alcohol and CO2 — it's mandatory for every wine. Malolactic fermentation is done by bacteria, mainly Oenococcus oeni, and converts malic acid into lactic acid — it's optional.
Why is malolactic fermentation sometimes blocked?
In aromatic whites like Sauvignon Blanc or Riesling, it’s deliberately blocked to preserve the sharp acidity and freshness that define those wines.
In which wines is malolactic fermentation actually wanted?
In reds and in fuller-bodied whites like Chardonnay, where it gives a rounder, buttery texture.
When does malolactic fermentation happen relative to alcoholic fermentation?
Weeks or months later, often while the wine is already in barrel.