Malolactic Fermentation Explained: Why Some Wines Taste Buttery and Others Stay Crisp

Taste a glass of creamy, rounded Chardonnay next to a zesty Sauvignon Blanc and the difference is obvious. Part of that contrast comes from the grape and the climate, but part of it often comes from a quiet step in the cellar that most wine lovers have heard of yet few can explain: malolactic fermentation, usually shortened to “malo” or MLF.

What is malolactic fermentation?

Grapes contain two main acids: tartaric acid and malic acid. Malic acid is the same sharp acid you notice in a green apple. During malolactic fermentation, lactic acid bacteria – most commonly Oenococcus oeni – convert malic acid into lactic acid, the softer acid associated with milk and yogurt, releasing a small amount of carbon dioxide along the way.

Strictly speaking, it is not a true fermentation in the way alcoholic fermentation is: no sugar is turned into alcohol, and it is driven by bacteria rather than yeast. Many winemakers therefore prefer the term “malolactic conversion.” It usually takes place after the alcoholic fermentation has finished, although it can overlap with it.

What does it change in the glass?

1. Softer acidity

Because lactic acid is perceived as gentler than malic acid, the wine tastes less sharp and its total acidity drops. This is especially useful in cool regions, where grapes can be harvested with very high malic acid.

2. A rounder, creamier texture

Wines that have gone through malo often feel fuller and smoother on the palate. Combined with ageing on the lees (the spent yeast cells), this gives the familiar creamy mouthfeel of many barrel-fermented whites.

3. Buttery aromas

The bacteria can produce a compound called diacetyl, which smells of butter. In small amounts it adds richness; in large amounts it can dominate. Winemakers can influence how much diacetyl remains – for example, by keeping the wine in contact with yeast lees, which can reduce it.

4. Greater stability

Once malic acid has been consumed, there is less risk of an unwanted malolactic fermentation starting in the bottle, which could leave a wine slightly fizzy and cloudy. This is one reason malo is so common.

Which wines go through malo?

Red wines: almost all quality red wines complete malolactic fermentation. It softens their acidity and helps make them stable for ageing.

White wines: here it is a stylistic choice. Many Chardonnays, including much of white Burgundy, undergo full or partial malo. In contrast, aromatic and crisp styles such as Riesling, Sauvignon Blanc and Grüner Veltliner are usually made without it, to preserve fresh fruit and lively acidity.

Sparkling wines: practice varies between houses. Some Champagne producers encourage malo for a softer base wine; others block it to keep extra tension and freshness.

How do winemakers control it?

Malo can start naturally from bacteria present in the winery, or be triggered by adding a selected bacterial culture. To prevent it, winemakers typically add sulfur dioxide, keep the wine cool, and remove bacteria through fine filtration. Some winemakers allow only part of a batch to complete malo, then blend it back – a simple way to fine-tune the balance between freshness and roundness.

Malo and Vietnamese food

Understanding malo is surprisingly useful at the table, especially with Vietnamese cuisine, which balances sour, sweet, salty, spicy and herbal flavours in a single meal.

• Crisp, non-malo whites (Riesling, Sauvignon Blanc) suit dishes driven by lime, fresh herbs and tangy dipping sauces – think gỏi cuốn (fresh rice-paper rolls with shrimp and herbs) or gỏi (Vietnamese salads with green papaya or banana blossom). Their bright acidity matches the dish’s own sourness.
• Rounder, malo-softened whites such as a lightly oaked Chardonnay work better with richer, gentler dishes: chả cá Lã Vọng (Hanoi turmeric fish fried with dill), crab cooked in butter and garlic, or cà ri gà (Vietnamese chicken curry with coconut milk). The creamy texture echoes the fat and coconut.
• Avoid very buttery whites with fiery chilli: high alcohol and heavy oak tend to amplify heat, while a lighter, fresher wine keeps the palate refreshed.

📖 Glossary

• Malic acid: a sharp, green-apple-like acid naturally found in grapes.
• Lactic acid: a softer acid produced during malolactic fermentation.
• Oenococcus oeni: the main species of lactic acid bacteria used in malolactic fermentation.
• Diacetyl: a by-product of malo with a buttery aroma.
• Lees: spent yeast cells and other particles left after fermentation.
• Partial malo: allowing only a portion of the wine to complete malolactic fermentation before blending.

Next time a wine strikes you as either razor-crisp or soft and creamy, ask yourself: did it go through malo? It is one of the clearest examples of how a winemaker’s choices shape what ends up in your glass.

Please enjoy responsibly. Never drink and drive. Intended for adults of legal drinking age.

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