Learn
Oak
Where vanilla, toast and butter come from — and why they are not the grape.
The short answer
Oak does three separate things: it can add flavours of its own, it adds a little tannin — the drying, grippy sensation you notice in red wine — and it lets a very small amount of oxygen reach the wine. New barrels do all three strongly; old ones mostly just the last.
Overview
A great many flavours people attribute to grapes actually come from the barrel or from bacteria.
Vanilla, toast, coconut, cedar and sweet spice come from oak. New oak gives much more of this than old oak; American oak gives more vanilla and coconut than French.
Butter comes from malolactic conversion, a bacterial process that softens acidity. It is not oak and not the grape.
Creaminess and a bready character often come from time spent on dead yeast cells.
This matters practically. If you dislike Chardonnay, you almost certainly dislike oak and butter rather than the grape — which is why Chablis, made from the same grape without either, is the standard recommendation.
Oak does three things to wine, and they are worth separating because they are often lumped together.
It adds flavour. Toasting the barrel during construction generates vanillin, lactones, furfural and guaiacol, which read as vanilla, coconut, toast, caramel and smoke. How much depends on how new the barrel is: a first-use barrel gives a great deal, a fourth-use barrel almost none.
It allows slow oxygen ingress. A few milligrams per litre per year enters through the staves, which softens tannin, stabilises colour and develops complexity. That is why oak ageing matters even in a neutral barrel that adds no flavour at all.
And it concentrates, slightly, through evaporation — the reason barrels need topping up.
Species matters. American oak (Quercus alba) is higher in the lactones responsible for vanilla and coconut and gives a more overt flavour; French oak (Q. robur and Q. petraea) is subtler and more tannic. The Rioja style rests substantially on the first, Bordeaux on the second.
Oak chips and staves deliver flavour without the oxygen exchange or the cost. They are legal in most jurisdictions and widely used at the lower price points, and they are the reason an inexpensive wine can taste oaky without having been near a barrel.
Where you can see it
- Obvious oak
- A traditional Rioja Reserva spends years in barrel and tastes of it — vanilla, sweet spice, a softness the wine did not start with.
- No oak at all
- Chablis is Chardonnay without new oak. Comparing it to an oaked Chardonnay is the fastest way to learn what oak actually contributes.
What people get wrong
2 widely repeated claims this page corrects.
Not true
“Buttery Chardonnay tastes that way because it was aged in oak.”
The buttery note comes mainly from malolactic fermentation, not from the barrel. Oak contributes other things — vanilla, spice, texture — but butter is not usually one of them.
Oversimplified
“After a few uses a barrel is neutral, so an old barrel is basically a steel tank.”
The extractable flavour compounds do fall away with use, but the barrel still admits oxygen and still has a large surface area. A neutral barrel is not an inert vessel.
Go shallower or deeper
The beginner page and the chemistry page are both correct, and neither substitutes for the other.
Sources
Sources consulted
- WSET educational materials and the Systematic Approach to Tasting — Wine & Spirit Education Trust