Malolactic fermentation is basically a hug

There's a softness that hits your tongue and doesn't let go. It doesn't shout. It doesn't sparkle. It settles in, warm and slow, like someone who finally says, “I'm here.”

That's malolactic fermentation. You might not know the name. Most people don't. But you know the feeling. It's part of why a rich, golden Chardonnay can feel like a cashmere blanket wrapped around your ribcage.

The short answer: malolactic fermentation, MLF or “malo” for short, is when bacteria turn the wine's sharp malic acid into softer lactic acid. The wine tastes less tart, feels rounder, and can pick up a buttery note. Most red wines go through it. For white wines, it's a style choice.

The (very soft) science

Grapes contain malic acid, the same sharp tang as green apples (malum is Latin for apple). After the main fermentation, friendly lactic acid bacteria, above all one called Oenococcus oeni, convert it into lactic acid, the gentler acid of yoghurt and milk, and release a little carbon dioxide (AWRI).

That's why it's called a secondary fermentation, even though no yeast is involved. It's transformation by softening. Chemistry that whispers instead of wails. And suddenly that edgy, acidic wine becomes creamy. Round. Not just in taste, but in soul.

• Pre-malo: a crisp slap.
• Post-malo: a long, slow exhale.

Where the butter comes from

The buttery smell has a name too: diacetyl, made by the bacteria during malo. The vanilla and toast in an oaky Chardonnay are something else: they come from the barrel. Butter from the bacteria, vanilla from the oak, fruit from the grape. Together, that's the warm, rich Chardonnay people either adore or swear off.

Which wines go through it

• Most reds. Almost all red wines go through malo. It softens them and makes them more stable in the bottle. In reds it's quieter, less spotlighted.
• Rich whites, above all Chardonnay. Here malo gets to sing, loud and lush: creamy texture, softer acidity, sometimes that buttery note.
• Crisp, aromatic whites such as Riesling and Sauvignon Blanc usually skip it, to keep their snap and their fruit.
• Sparkling wines: some go through it and some don't. In Champagne it's part of each house's style.

Some winemakers let it happen. Others stop it, by keeping the wine cold, adding sulfur dioxide or filtering out the bacteria. Some steer it halfway, blending wine that went through malo with wine that didn't: a dance between zing and silk.

It's not about better or worse. It's about the kind of comfort you crave. Do you want the pillow? Or the push?

Science that hugs

Malolactic fermentation is not just a process. It's a choice. A transformation that says: you don't have to be sharp all the time. You can soften. You can yield.

So next time someone hands you a glass of oaky Chardonnay, all warm vanilla, melted butter and toasted calm, know that it's not just the oak. It's not just the grape. It's science that hugs.

Some wines sparkle. Others soothe. Malolactic does the latter, and sometimes that's exactly what we need.

Studying it for an exam? Read malolactic fermentation in Chardonnay. For the opposite mood, try carbonic maceration is basically a pop song.

Questions people ask