Part IV · How wine is made · 3 min
Oak, tannin and time
What a barrel adds beyond storage, and how to tell whether a wine will improve if you wait.
What oak does
A barrel does three separate jobs, and people usually only notice the first.
- It adds flavour - vanillin (vanilla), lactones (coconut), furfural (toast, caramel), eugenol (clove). None of these exist in grapes.
- It adds tannin - oak tannin is structurally different from grape tannin and contributes grip and ageing capacity.
- It admits a trickle of oxygen - micro-oxygenation through the staves softens tannins and stabilises colour. I think this is the most important of the three, and it is certainly the least visible.
| Variable | Options | Effect |
|---|---|---|
| Origin | French vs American oak | French is subtler and spicier; American is louder, sweeter, coconut and dill |
| Age | New vs used | A new barrel gives strong flavour; by its third or fourth fill it’s mostly just a vessel |
| Size | Barrique (225 L) vs foudre (1,000 L+) | Smaller means more surface area per litre, so more oak influence |
| Toast | Light to heavy | How hard the staves were fired: light gives spice, heavy gives smoke and coffee |
A new French barrique costs well over €1,000, which is around NZ$2,000, and is a real cost line in any wine that uses them. When a cheap wine tastes strongly of vanilla and toast, it usually met oak chips or staves in a tank rather than a barrel, which gives the flavour but none of the slow oxygen exchange.
What tannin actually is
Tannins are polyphenols, and they bind to proteins. The drying, gripping feeling is them binding to the proteins in your saliva and stripping the lubrication out of your mouth. That’s why tannin is a feeling rather than a flavour.
It also explains the oldest pairing rule there is. Tannin binds to protein, so it binds to the protein in a steak instead of to your saliva. The wine tastes softer and the meat tastes less fatty. It’s one of the few pairing rules with a genuine mechanism behind it.
Will this wine improve?
Most wine won’t. Something like 90 percent of all wine made is intended to be drunk within a year or two, and putting it away does nothing but make it duller. Ageing potential needs a structure to preserve, and that means some combination of four things.
- High acidity - the single best predictor. It’s why Riesling and Nebbiolo outlive wines twice their weight.
- Firm tannin - a preservative and an antioxidant, which softens and integrates over years.
- Concentration - low yield, intensely flavoured fruit with something to give up slowly.
- Residual sugar - in the great sweet wines, another preservative entirely.
What ageing actually does: primary fruit fades and tertiary character arrives - leather, mushroom, forest floor, dried fig, tobacco. Tannins polymerise into longer chains, which feel softer and eventually drop out as sediment. Colour shifts, reds toward brick, whites toward gold.