Science
Why can Chardonnay taste buttery?
Malolactic fermentation, diacetyl, lees and oak — four contributors that usually travel together, only one of which is the actual cause.
The short answer
The buttery character comes principally from diacetyl, a compound produced by lactic acid bacteria during malolactic fermentation. Oak, lees ageing and ripeness contribute to the richness that surrounds it, but the butter itself is bacterial, not wooden.
Overview
This is the most common single question about the most planted white grape in the world, and the answer most often given is wrong.
Chardonnay itself is fairly neutral aromatically, which is exactly why it takes winemaking so well and why the style question dominates it.
How it works
The mechanism, at the scope it has actually been established.
Malolactic fermentation converts sharp malic acid into softer lactic acid. That alone changes the texture, lowering acidity and making the wine feel rounder.
Diacetyl is produced as an intermediate in that bacterial metabolism, and it is associated with buttery and buttered-popcorn characters. How much survives depends on temperature, oxygen, the bacterial strain and how long the wine subsequently rests on its lees — yeast can reduce diacetyl to compounds nobody notices.
Lees ageing adds its own contribution: texture, weight, and savoury bready notes from yeast autolysis. Stirring the lees increases the effect.
Oak contributes vanillin, oak lactones and toast compounds, and — if the barrel is new — wood tannin. It also admits a little oxygen, which changes texture. None of that is diacetyl.
Ripeness underlies everything. Riper fruit gives more body and more stone-fruit character, which is the canvas the rest sits on.
The four are done together because they suit each other, which is why they get attributed to whichever one is printed on the label.
Why it matters in the glass
It gives a reader a much better question to ask. Someone who wants a leaner Chardonnay should be looking for wines that blocked or partially blocked malolactic fermentation — Chablis being the classic case — rather than simply avoiding the word "oaked".
And someone who likes it now knows that an unoaked Chardonnay is not necessarily a way of avoiding it.
Where you can see it
- Chablis
- Cool site, generally little or no new oak, and producers who commonly restrict malolactic fermentation to keep the wine taut. The reference point for lean Chardonnay.
- Classic Californian Chardonnay
- Ripe fruit, barrel fermentation, full malolactic conversion and lees stirring — the style that made the association famous.
- Modern white Burgundy
- Frequently uses less new oak than it did a generation ago, which has moved the style without changing the grape.
What people get wrong
1 widely repeated claim this page corrects.
Compounds named on this page
Where a compound comes from is chemistry; what it smells like is perception. These are kept apart deliberately.
- Diacetyl — 2,3-butanedione
- A bacterial by-product of malolactic fermentation, associated with buttery character. Associated with butter, buttered popcorn, butterscotch. Reported in the region of a few milligrams per litre in white wine, and considerably higher in red where other components mask it. Caution: Malolactic fermentation does not guarantee buttery character. Yeast and bacteria can reduce diacetyl further to compounds nobody notices.
- Vanillin
- An oak-derived compound, chemically identical to the principal flavour compound in vanilla. Associated with vanilla. Caution: Extraction falls sharply with each use of a barrel, so vanilla character is largely a function of new oak rather than of oak as such.
- Oak lactones
- Oak-derived compounds associated with coconut and woody character. Associated with coconut, wood, sweet spice. Caution: Concentration differs between oak species, and American white oak is generally reported higher — a real difference that does not license "American oak tastes of coconut" as a universal.
How much diacetyl survives a given malolactic fermentation is not predictable from the fact that it happened. Bacterial strain, temperature, oxygen and subsequent lees contact all bear on it, which is why “did it go through malo?” is a less precise question than it sounds.
Go shallower or deeper
The beginner page and the chemistry page are both correct, and neither substitutes for the other.
Sources
Sources consulted
- The Australian Wine Research Institute — AWRI
- Bourgogne Wine Board (BIVB) — Bureau Interprofessionnel des Vins de Bourgogne
- WSET educational materials and the Systematic Approach to Tasting — Wine & Spirit Education Trust
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