How is oak used in winemaking?
Oak is an integral part of wine’s history, although its use nowadays is prompted by very different reasons than it once did. Driven by necessity, the ancient Romans would use oak barrels to store and transport wine, but it wasn’t until the 1800s that producers realised their barrels could add flavour, aroma and complexity to their creations. Fast forward to today, and when steel, plastic and even cement vessels are all valid aging and storage options, oak has become a deliberate choice for many winemakers.
What does oak do to wine?
Oak affects wine in three main ways:
- It adds flavour compounds, such as aromas of vanilla, clove, smoke and coconut.
- It allows for the slow intake of oxygen, which helps make wine smoother and less astringent.
- It provides the right environment for particular metabolic reactions to take place (such as malolactic fermentation), which makes wines taste creamier.
Because winemakers are not permitted to add flavour additives to their wines, oak has become an accepted way of affecting its taste. A large proportion of oak is hemicellulose, which acts as a binding agent in the wood itself, and is mostly made up of small sugars such as xylose and arabinose. Not only can these sugars be hydrolysed when in contact with wine, but they decompose when heated (or ‘toasted’), forming compounds like furfural, maltol and ethoxylactone which can give roasted, malty and caramel notes.
Reds that commonly benefit from the use of oak include Pinot Noir, Cabernet Sauvignon, Merlot and Syrah, while whites include Pinot Grigio, Sauvignon Blanc and Chardonnay.
What factors affect the way oak influences wine?
There are a host of oak variables that will affect a wine, and winemakers will choose barrels based on a specific array of criteria, so as to achieve their desired flavours and textures. These factors typically include:
- Where the oak is from
- Regional variations across different forests
- The way the oak was dried
- The way the oak was toasted
- The way an individual barrel has been used before
- The length of time the wine is left in oak
Where do oak barrels come from?
The two most common types of barrel used in winemaking come from America and France – although Hungarian and Slavonian barrels have found favour with some winemakers. Each have their pros and cons. American oak barrels, for example, are cheaper than French barrels and tend to have a bigger impact on a wine’s flavour and aromatic elements. French oak barrels, however, are widely regarded as the wine industry’s gold standard, as they offer higher wood tannins and tighter wood grains. This tends to have less influence on the wine’s flavour, instead contributing more to the wine’s overall palate presence. However, they are considerably more expensive – around three times the price of American barrels and often running over £1,000, depending on where they’re sourced from. So you can see the scale of financial investment that wineries face on a daily basis.
What’s the difference between old and new oak?
In a nutshell, the newer the barrel, the more concentrated the oak’s influence will be on the wine – with every vintage, it’ll lose some of its flavour-giving properties. Think of it as a tea bag: the first time it’s infused with hot water you’ll get full flavour, but each successive use will produce a weaker cup of tea.
As such, winemakers that incorporate stronger oak flavours in their wines will find themselves spending a considerable sum on barrels. Some producers, however, will age a portion of the wine in new oak in order to impart some flavour and complexity, before blending it back with the rest of the wine which was aged in older oak – this gives the wine some character, while saving on barrel costs.
Older oak barrels are still able to provide some more nuanced flavours, however, and they continue to play a role insofar as oxygen is concerned. While oak holds liquid without leakage, a miniscule amount of oxygen can permeate the wood – this has a big impact on the natural chemical conversions that wine undergoes during fermentation and maturation.
Does size matter?
It certainly does. Wine barrels come in a variety of sizes, and the smaller the barrel the greater the impact the oak will have on the wine, due to a higher percentage of the wine being in contact with the wood. As such, finding a balance of age, oak provenance and size in relation to output can be a complex mathematical equation where costs are concerned.
What barrel preparation factors influence oak’s effect on wine?
As well as the size and type of oak used, the way a barrel is dried and toasted will have an impact on the wine it holds. A barrel’s staves need time to dry in the open air before they’re used – most coopers insist on at least 24 months of maturation to reduce ‘greenness’ and astringency, while 36 months offers more subtle characters (for a price, of course).
When the staves are ready to be made into a barrel, the cooper applies a heating process and is able to control its ‘toast’ levels – typically light, medium and dark. The greater the toast, the higher the oak’s influence on the wine’s colour, aroma, flavour and overall style.
How long are wines aged for in oak barrels?
This depends entirely on the winemaker’s intention for the wine, although it usually takes several months for oak to begin imparting its characteristics. According to Wine Folly, some typical aging regimes include:
- Pinot Noir: 10 months in old French oak
- Chardonnay: 13 months in 50% new French oak
- Gran Reserva Rioja: 24 months in 40% American and 60% French oak
- Zinfandel: 17 months in 20% new American barrels
Of course, this will vary widely between producers and vintages. And remember, not all winemakers use oak – some of the most renowned producers, such as Chateau Petrus and Lafleur, choose to use alternative materials such as stainless steel and cement.
A word on oak chips
Oak barrel aging can be time consuming, expensive and – particularly for new wines or inexperienced winemakers – a matter of trial and error. As such, some winemakers choose to achieve an oakiness using oak chips instead. While this can be a more affordable way of adding some of the toast and vanilla notes that oak barrels are known for, it does not provide any of the textural benefits. A lot of purists also take a dim view of the practice, with Old World winemaking regulations only legally permitting oak chips since 2006.