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Silent Partner: Oak Flavour and Grapes

Grapes and oak flavour are natural partners. When used well, oak can add as much to a wine’s flavour as the grapes themselves, as BEVERLEY BLANNING MW discovers.

Have you ever thought of trying to improve your wine by adding a touch more flavour? Maybe a few drops of vanilla essence in your Chardonnay? A pinch of pepper in your Shiraz? We like to think of wine – especially fine wine – as an unadulterated product of the soil. But when it comes to using oak in winemaking, these ideals fly out of the window.


Our infatuation with obviously oaky wines may have waned, but we are still in love with oak. Oak barrels allow slow oxygenation of wine and benefit its structure. But oak is also preferred because its flavours and aromas marry so well with those of wine. In many cases, the influence of oak on a wine’s flavour is probably as important as the grapes themselves.

Oak is a natural product, but there is nothing innately natural about its use in winemaking. We can make, age and store wine perfectly well using a variety of modern, inert materials. But there is no denying the perceived value of oak.

Winemakers today have a multitude of choices of oak-derived products to use to flavour their wines, including barrels, inner staves, chips and powder. Oak chips come in a mouthwatering range of flavours, such as ‘premium dark roasted’, ‘toasted’ or ‘high vanilla’. Oak powder sounds rather less appealing, but even here you can choose to sprinkle American or French oak.

Winemakers are reluctant to admit to using these ‘lesser’ forms of oak products, despite the fact that the flavour compounds they contain are identical to those found in oak barrels. Opponents maintain that their use should be banned, or at least heavily restricted, on the grounds that they are a kind of aromatisation. This is ironic considering that it is largely for its aromatic properties that oak is valued.

Flavour Spectrum

Napa-based company World Cooperage has devised an aroma wheel (see p83) showing the astonishing array of wine flavours from oak, including such descriptors as sweet, creamy, vanilla, yeasty, nutty, smoky and spicy. But the specific, oak-derived characteristics in any particular wine will depend on many variables. There are hundreds of different species of oak, of which very few possess the qualities needed to make wine barrels. The most common are French oak (Quercus robur and Quercus sessiflora) and American oak (Quercus alba). The difference in species accounts for the major variations in flavour and aroma between French and American oak, rather than their geographical origin. As well as the type and provenance of the oak, of crucial importance to oak flavour is how the wood is treated by the cooperage. Only by long, slow seasoning, does oak lose its harsh woody character.


Matt Gant, winemaker at St Hallett in Barossa, describes the difference he sees in his wines aged in various types of oak: ‘American oak gives weight and richness, whereas French oak gives complexity and finesse,’ he says. Explaining the different flavour profiles, he adds: ‘American oak gives primary vanillin, coffee and chocolate flavours. With French oak, the flavours creep up on you. Smoky, spicy, peppery characters develop over time.’

French oak is still seen as the gold standard for quality, but the same species of oak from other parts of Europe – Hungary, Poland or Russia, for example – can also give very good results. At a recent blind tasting in London of wines aged in French, American and Polish oak, the wine aged in Polish oak was the preferred choice of many.

The way to add specific oak flavours and aromas to wine is by toasting. Dr Jim Swan, a consultant specialising in the influence of oak barrels on wine, considers that, ‘toasting is responsible for 70–80% of oak flavour.’ Toasting is the process that takes place after the initial heating of the wood staves in order to bend them into a barrel shape. The barrel is toasted over a fire for 5–15 minutes, depending on the level of toast desired. Aromas are formed as the structure of the wood changes.

The temperature and duration of toasting will determine the flavours and aromas imparted to the wine. This is an inexact science. Each cooper will have a slightly different interpretation of what temperature and length of heating is required for light, medium or heavy toast.

At a recent seminar I attended, organised by Cognac-based cooperage Taransaud Tonnellerie and the Institute of Masters of Wine, participants were initiated into the curious world of oak aroma compounds such as beta methyl gamma octa lactone – that’s coconut aroma to you and me. Taransaud’s head of research and development, Dominique de Beauregard, explained that at heavier levels of toasting, smoky, woody, caramel and spicy aromas are formed. In contrast, less toasted barrels tend to emphasise the fruit in the wines.

Taste Test

To test these theories, we tasted red and white wines that had been aged in barrels with different levels of toasting and compared these with the same wines with no oak influence. The aromas of the white wine varied from hazelnut, through buttery, and oaky, to rich and toasty at different levels of toasting. In each case, the oak sweetened and softened the rather acidic base wine.

For the red wine the results were even more dramatic. The simple, fruity, fairly nondescript wine was transformed by barrel ageing. Even at a light level of toasting, complex aromas of cloves, spice, coffee and toast were detectable. Higher levels of toast emphasised these characters further, with increasing levels of pepperiness and coconut becoming apparent. In each case, the oak made a simple wine taste more interesting, although the additional tannins in the wood did confer varying amounts of astringency and bitterness to the wine.

At World Cooperage, researchers have come up with something they call ‘Barrel Profiling’, a range of different toasting options which promise winemakers predictably ‘definable flavour profiles’. One winery which has just started using this system is Rodney Strong in California’s Sonoma Valley. Winemaker Rick Sayre explains: ‘The idea is to target different profiles of oak characteristics for different wines and different styles of wine – Pinot Noir, Cabernet and Chardonnay, for example. We’re trying to use science to take the guesswork out of using barrels.’ Swan explains that, ‘toast used to be based on colour – light toast being a light colour, medium toast a medium colour and so on. But we now know that most flavours are not related to colour. So we can toast a barrel with a temperature sensor to make the flavours we want to make and to achieve greater consistency.’

But St Hallett’s Gant believes there is no easy substitute for doing the work yourself: ‘It’s such a vital part of the process,’ he says, ‘yet there’s not enough emphasis placed upon it. You need to use a range of coopers and trial each one with your own wine. And you need to keep on doing it, because things change all the time.’

For a new producer, these are choices which must seem even more daunting. English couple Philip and Sarah Isles moved from London to Château Lezongars in the Premières Côtes de Bordeaux in 1997. Philip’s philosophy on oak is to use different barrel makers, different levels of toast and different kinds of oak, with the aim of adding complexity. But he admits that choosing oak is a lottery: ‘You just have to suck it and see,’ he says.

Another relative newcomer is American Alex Gambal, a former real estate broker now making wine in Burgundy. He considers oak ‘one of the most fascinating pieces of the puzzle’, but is aware of the risks, having lost a barrel of Meursault a few years back due to an unidentified problem with the barrel. His advice on using oak? ‘If you find a barrel maker who suits you stylistically, stick with them and pray they don’t change.’

Oak is one of the biggest expenses a winemaker has, yet often the thing he knows least about. Even the most experienced winemakers are still learning. Ridge’s Paul Draper says he still conducts ‘14–21 oak experiments with the Monte Bello Cabernet every year’. As he points out, we have learned a great deal about oak from a tasting perspective, but there is a lot more to learn. ‘Each cooper has a huge influence on the wine. You’re at their mercy. When you taste the wine in different barrels, it’s a bit frightening to see how much influence oak has.’

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