Looking at the relationship between oak and wine
The basics: What is oak?
According to Jancis Robinson in the Oxford Companion to Wine, “oak is a hard, supple, watertight wood, which [displays] a natural affinity with wine…”. While you can make barrels out of many different types of wood, only oak barrels will positively influence wine. Within the oak family, there are hundreds of different species the genera of which are too numerous and complicated for a blog post. For winemaking, there are three kinds that are the most important: American white oak (Quercus alba), European oak (Quercus petraea) and pendunculate oak (Quercus robur).
American oak can be found all over the eastern United States, while European and pendunculate oak grows throughout Europe (France, Slovenia, Russia and Hungary being the most usual sources). Much like grapes, the terroirs of the forests where the trees are grown can be as influential to the final wood flavours and characteristics as the type of wood itself and so winemakers are often very particular about from where they source their barrels.
When making the Wildeberg White 2018, winemaker JD Rossouw said that the wine in the Austrian oak barrels “just kept jumping out” at him with its bright acidity and textural mouthfeel.
We don’t have the time or space here to delve into how individual species impart their subtle differences and vast array of aromas into the wine. Indeed, each individual tree is a living, changing entity with which different grape varieties may react in different ways. Generally speaking, American oak gives more obvious oak flavours like vanillin and coconut. The aromas are also very powerful and so American oak has traditionally been reserved for big, powerful reds like Australian Shiraz and Rioja. European oak, on the other hand, imparts less overt flavours such as toast and coffee, but leaves the wines more subtle and smooth.
The Toast of the Town
As well as the type and source of the wood, winemakers are also very particular about the techniques used in the production of their barrels. While the production process has numerous steps, all of which contribute to the final wood’s flavour, arguably the most important and influential stage is the ‘toasting’ or ‘chauffe’, whereby the oak is heated to allow it to be bent into shape. This process also degrades the structure of the wood, releasing aromatic compounds. The toast acts as a buffer between the tannin in the wood and the alcohol in the wine; the higher the level of toast, the less tannin is extracted by the alcohol into the wine.
In very general terms there are three levels of toasting:
Light toast: the lowest level with little colour change in the wood. Lightly toasted barrels will keep the wines fruity and impart plenty of tannin.
Medium tannin: some browning to the wood. The wines will be rounder, smoother and less tannic with vanilla and coffee flavours.
Heavy toast: very dark wood. These wines will gain roasted coffee, clove and smoked meat flavours, but pick up little tannin from the barrel.
The final consideration in the production of barrels is the size. Simply put, the smaller the barrel, the lower the ratio of surface area to wine, so the more it impacts the wine. Barriques (usually about 225-300 litres) will result in more oak flavours, while large casks (from 500 litres) will soften a wine’s acidity and integrate tannins without giving strong oak aromas; this is why many Italian wineries use very large casks to soften the naturally high acidity of varieties like Nebbiolo and Sangiovese. The botti at Il Cascinone range from 500 litres all the way up to 70 hectolitres! Many of their wines are blended from wines aged in each size, giving both complexity and intriguing mouthfeel.
Avamposti Pinot Nero 2016 is a blend of 4 different parcels, fermented in 4 different ways. Once blended the wine was aged in a mixture of barriques and tronconiques to increase the complexity of flavour at bottling.
Respect Your Elders
The younger the wood, the more influence it has on the wine. Even after just one use, the oak’s influence is significantly reduced. If the wood aromas are key to the wine, then it’s common for barrels to be replaced (or shaved and re-charred) after two or three years. If the aromas are not as important and the barrels are used to soften and round out the wines, then barrels can be used for many years.
Of course, the wood doesn’t just impart flavours but also absorbs them. If these barrels are then used with different liquid, these flavours can be released into the new juice, such as Port barrels being used to age North American Whiskies. Our Decagon Cabernet Franc spends 5 months in old Cognac barrels enhancing its complexity with softer fruit and burnt toffee flavours.
Given the work and precision that goes into making barrels to specification, it’s understandable that good barrels are not cheap. There are alternatives that can help to stabilise the colour and increase tannin in the wine, though they aid less with softening and rounding out the wine.
Oak chips: these can be made from either American or European oak and are usually medium to heavy toasted. They impart oak flavours and help to improve the mouthfeel of the wine.
Inner staves: large pieces of American oak, which are submerged into an inert tank during fermentation. They impart flavour, but don’t alter the smoothness of the wine very much.
Barrel inserts: pieces of American wood used inside old barrels to give oak flavours.
Toasted oak powder: imagine a giant tea bag filled with oak powder. They provide both flavour and tannin, however their use is banned in the EU.