Wood has long been used as a vessel for wine, historically more as a form of storage, but as understanding of the influence wood can have on wine became known, so wood, and oak in particular, has increased in importance. While some wines are fermented and aged entirely in relatively inert vessels such as stainless steel or concrete eggs, other wines are fermented in and or aged in oak.
Why oak? It is strong and supple and importantly for wine, tight grained so relatively watertight but allowing micro-oxygenation. It has a natural affinity to wine, imparting a range of flavours that are considered desirable. There are many different types of oak, but the main two are Quercus Alba and Quercus Robur, which are more commonly known as American and European oak respectively. American oak is more synonymous with creamy coconut and vanilla notes, European oak is more subtle with generally spicier characteristics.
Rioja is an example of a wine that has traditionally used American oak. With its often quite overt coconut characteristics, doing my wine exams, I’d pray for a Rioja to come up in a blind tasting as its usually fairly easy to pick out of a line-up for just that reason!
How is oak used in wine making?
The short answer is ‘many ways’. I won’t go into great detail but want to try and show how an oak barrel can have such an impact on a finished wine.
Fermentation – some grapes are fermented in oak barrels, or large open top vats, the retention of heat in the wood combined with the high solids to liquids ratio (the shape of the barrel) helping with extraction of colour and tannin in red grapes ,although this can be at the expense of fresh fruit characteristics. It is believed better integration can be achieved by fermenting as well as ageing wine in barrels. It’s not just for red wines though, high quality white Burgundy will often be fermented in barrels (and usually use new oak barrels).
Maturation – Because oak allows micro-oxygenation to take place through the tiny pores in the wood, the oxygen helps to softens tannins and stabilise colour amongst other things (it’s very scientific so I will just leave it at that if that’s ok?!). Note – Wines that are just matured rather than fermented in wood produces more pronounced lactones (aromas) in the wine.
Imparting flavour compounds –oak adds a variety of aroma compounds (lactones) to wine, with different compounds released by different levels of toasting the barrels (light versus heavy). The size of the barrel, new versus old oak and amount of time spent in barrel, also influences this.
Toasting the barrel: All barrels have to be seasoned before use, and oak staves need to be heated in order to bend them into the shape of the barrel. How long the barrels are heated impact on the level of ‘toast’ in the barrel – for example barrels can be lightly toasted, medium toasted, or heavily toasted (aka charred/burnt to a crisp!). This toasting produces a variety of aromatic compounds which influence the wine – producing aromas such as vanilla, coconut, clove, cinnamon, smoke, brioche, toasted bread, coffee and cocoa and roasted nuts.
Size of the barrel: The smaller the barrel the more interaction of surface area with the wine, so the greater the impact in terms of aroma compounds and oxygenation (softening tannins). Large neutral vats, allow gentle oxygenation to soften wine without imparting any overt oaky characteristics.
Did you know? Barrels come in all shapes and sizes, in France, Burgundy uses 228 litre barrels (known as barriques), Bordeaux uses 225 litre barrels, some producers in the Rhône use 600 litre demi-muids, and in Italy, the norm is to use larger oak casks and botti (500-10,000 litre).
New oak versus used oak: It stands to reason a newly toasted barrel will impart stronger characteristics on a wine than a barrel which has been used two or three times, the result will be less overt oak in an older barrel. Given the price of new oak barrels, new oak is very much the domain of higher prestige wines.
Time spent in barrel: Depending on the style light fruity red wines, may only be matured for a short time in barrel (3 to 6 months if at all) just for integration. However, the more astringent the tannins in the wine, the longer the maturation process needs to be as remaining in the barrel helps to soften these tannins. Also, the longer the wine is in barrel the greater the micro-oxidation which also helps clarify and stabilise the wine. Colour will also be impacted – for example, as an apple would brown with exposure to air, so a red wine will fading slightly in colour with flavours becoming more tertiary (showing development – mushroom, earthy, tar, smoke etc). Note – in white wines that are aged in oak, colours deepen not fade.
Top tip! – White wines which are more overt and fruit forward (think Riesling, Sauvignon Blanc) will generally not see any oak. Although increasingly producers especially in New Zealand are experimenting with ageing their Sauvignon Blanc in barrels, resulting in a more complex, mellower wine, less overt fruit, more rounded and weighty. If you like this style look for Greywacke Wild Sauvignon. A serious food wine.
The cheat’s alternative!
New oak barrels are expensive, and this cost obviously has to be passed onto the consumer through a higher bottle price which is why new oak is usually reserved for the best quality wines. Some winemakers want to have oak influence but don’t want to fork out for a barrel – the answer: Oak chips. Ok, it’s not cheating, but it doesn’t have the same results.
Hands up who can remember in the early 1990s opening a bottle of cheap Aussie Chardonnay, the liquid that poured into the glass was vivid yellow in colour and the nose smelt like butter? Yes, this is the type of influence oak can have on a wine when used badly (in my opinion) these oak chips dangled into a vat during and/or after fermentation and allowed to perforate into the wine. The result – oak characteristics without any of the integration you’d get from a barrel. It does keep the costs down, so you get what you pay for I suppose.
So there you have it, oak and how it can influence the style and flavour characteristics of a wine. Next up, “P” is for Picpoul de Pinet.