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Malolactic fermentation in Chardonnay: where the butter comes from
What malolactic fermentation does to Chardonnay, the compound behind the buttery smell, how winemakers turn it up or down, and how to tell it apart from oak.
Updated October 2026
Rewritten by Alper Billik, Advanced Sommelier
4 min read
The short answer: malolactic fermentation (MLF, or “malo”) is a second fermentation in which bacteria turn sharp malic acid into softer lactic acid. In Chardonnay it lowers the acidity, rounds the texture and can add a buttery note from a compound called diacetyl. Vanilla and toast come from oak, not from malo; bread and biscuit come from the lees.
What malolactic fermentation is
- What happens: lactic acid bacteria, above all Oenococcus oeni, convert malic acid, the tart acid of green apples, into lactic acid and a little carbon dioxide.
- Why it matters: the Australian Wine Research Institute (AWRI) gives MLF three roles: it lowers acidity, it stabilises the wine by removing malic acid that bacteria could otherwise feed on in bottle, and it shapes aroma and flavour.
- When: most often after the alcoholic fermentation (sequential), or by adding the bacteria with the yeast (co-inoculation). It can start on its own or with a selected bacterial strain.
- Which wines: virtually all reds, many whites and many sparkling base wines. For white wine, it is a style decision.
Chardonnay aromas and where they come from
| Aroma | Main source |
|---|---|
| Butter, butterscotch | Diacetyl, made by the bacteria during MLF from the wine's citric acid |
| Creamy, round texture | Lower acidity after MLF, plus time on the lees |
| Vanilla, coconut | Oak: vanillin and oak lactones, more of the latter in American oak |
| Toast, smoke, clove | Toasted barrels: guaiacol, eugenol and other toasting compounds |
| Bread, brioche, biscuit | Ageing on the lees, as dead yeast cells break down |
| Green apple, lemon, pear | The grape itself; brighter when MLF is blocked |
| Peach, melon, pineapple | The grape in a warmer climate |
- Butter, butterscotch
- Main sourceDiacetyl, made by the bacteria during MLF from the wine's citric acid
- Creamy, round texture
- Main sourceLower acidity after MLF, plus time on the lees
- Vanilla, coconut
- Main sourceOak: vanillin and oak lactones, more of the latter in American oak
- Toast, smoke, clove
- Main sourceToasted barrels: guaiacol, eugenol and other toasting compounds
- Bread, brioche, biscuit
- Main sourceAgeing on the lees, as dead yeast cells break down
- Green apple, lemon, pear
- Main sourceThe grape itself; brighter when MLF is blocked
- Peach, melon, pineapple
- Main sourceThe grape in a warmer climate
Diacetyl is the one to remember. The AWRI notes that butteriness can be masked by strong oak or very fruity wines, and that very high levels read as overtly buttery and undesirable.
How winemakers turn the butter up or down
- All, some or none. A winemaker can let every barrel go through malo, block it, or blend malo and non-malo wine for a middle way. MLF is blocked by keeping the wine cold, adding sulfur dioxide or filtering out the bacteria.
- Lees contact lowers butter. Yeast turns diacetyl into acetoin and 2,3-butanediol, which barely smell. Long contact with the lees means less butter.
- Timing. Co-inoculation tends to give fruitier wines with less buttery character, and a faster MLF tends to leave less diacetyl.
- Strain, temperature and pH. Some bacterial strains make much more diacetyl. In AWRI's figures, MLF at 18°C leaves more than at 25°C, a longer MLF leaves more, and lower pH favours it.
Chardonnay styles and malo
- Classic white Burgundy usually goes through malo, often with lees ageing in barrel. The result is more creamy texture than obvious butter.
- The classic “buttery” New World style combines full malo with new oak: butter from the bacteria, vanilla and toast from the barrel.
- Crisp, fruit-led Chardonnay often has malo blocked, or only partly done, to keep fresh acidity and apple and citrus fruit.
- Champagne and other sparkling wines differ by producer: some use malo, some block it. It is part of house style.
How to spot malo in a blind tasting
- Butter or butterscotch on the nose, with a rounder, creamier palate: malo is likely.
- Vanilla, toast, coconut: that's oak. It can come with or without malo.
- Sharp acidity and green apple: malo probably blocked or partial.
- Careful: long lees contact can remove the butter after a full malo, so no butter does not prove no malo.
Want the gentle version? Read malolactic fermentation is basically a hug. For the other two sources of Chardonnay's richness, see the world's wine barrels and sur lie ageing.
Quick quiz
Question 1
Which bacterium carries out most malolactic fermentations?
- a)Saccharomyces cerevisiae
- b)Oenococcus oeni
- c)Botrytis cinerea
- d)Brettanomyces
Show answerAnswer
b) Oenococcus oeni. Oenococcus oeni survives wine's alcohol and low pH. Saccharomyces is a yeast, Botrytis a fungus.
Question 2
What does MLF convert?
- a)Sugar into alcohol
- b)Tartaric acid into malic acid
- c)Malic acid into lactic acid
- d)Alcohol into acetic acid
Show answerAnswer
c) Malic acid into lactic acid. Sharp malic acid becomes softer lactic acid, with a little carbon dioxide.
Question 3
Which compound gives the buttery smell?
- a)Diacetyl
- b)Vanillin
- c)Geosmin
- d)Ethanol
Show answerAnswer
a) Diacetyl. Diacetyl, made from citric acid during MLF. Vanillin comes from oak; geosmin is an earthy taint.
Question 4
Which of these lowers the buttery character?
- a)A longer, slower MLF
- b)Long contact with the yeast lees
- c)A cooler MLF
- d)Choosing a high-diacetyl strain
Show answerAnswer
b) Long contact with the yeast lees. Yeast turns diacetyl into compounds that barely smell. The other three tend to raise it.
Question 5
Where does the vanilla in an oaked Chardonnay come from?
- a)Malolactic bacteria
- b)The lees
- c)The oak barrel
- d)The grape skins
Show answerAnswer
c) The oak barrel. Vanillin comes from the oak. Butter comes from malo, bread and biscuit from the lees.
Questions people ask
Does all Chardonnay go through malolactic fermentation?
No. For white wines it is a choice. Many rich and Burgundian-style Chardonnays go through it; many crisp, fruit-led ones block it or do only part.
Why does my Chardonnay taste like butter?
Most likely diacetyl from malolactic fermentation. If it also smells of vanilla and toast, new oak is adding to the effect.
Is buttery Chardonnay a fault?
No, it's a style. Only at very high levels does diacetyl become overpowering and count as a flaw.
Does malolactic fermentation make wine sweeter?
No. It doesn't add sugar. Lower acidity makes the wine feel softer and rounder, which some people read as sweetness.
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