The Origins of Wine Aroma, Part 5 - Oak
We've talked about the contributions of the grapes, the yeast, and the bacteria to wine flavor and aroma, but there's one particular storage vessel that is particularly associated with wine that adds its own contributions to the flavor and aroma profile: the oak barrel.
There are three major species of oak that are most commonly used for wine barrels-- Quercus robur, Quercus sessilis, and Quercus alba. The first two are European, and the last is American. Aside from looking different, they all provide something slightly different to wine. For example, barrels from the Central forest of France are typically made from Quercus sessilis and are more likely to contribute high aromatics to wines versus barrels made from the Limousin forest just south of it, where Quercus robur dominates and the wood has more tendency to contribute polyphenols (structural components) to the wine. Wine aged in American Quercus alba is likely to pick up even less phenolics from the oak than either of the French varieties, so winemakers looking for a softer oak profile would do well to look to American oak.
Barrel flavor goes beyond origin and species, however. Once the trees are felled, and staves cut, they need to be dried. This can take place either in a kiln, or out of doors-- usually 24 to 48 months. During this time, the moisture content in the wood drops to about 12%, the cellulose in the wood starts to break down into compounds that influence the character of the wine, and the tannins in the wood start to bind together, which has the effect of making them feel softer on the palate.
After drying, the staves will be shaped, and assembled into a barrel. After shaping, the staves will be raised, or stood in an upright circle held in place with a few hoops. At this point they need to be made somewhat malleable to get them into the characteristic barrel shape. This can be done by steaming or firing. If they're fired, they'll be sprayed with water during the firing in order to help with the bending.
Once the barrel is shaped, it is then toasted. Variations in the level of toasting will impact the flavors imparted to the wine with lighter toasts contributing more natural wood aroma and flavor, medium toasts contributing more vanilla and caramel, and darker toasts skewing more towards spicy and smoky tones.
Here at Aridus, we use a variety of oaks and toasts. For example, we really enjoy the flavors that Hungarian and Russian oak impart to our Chardonnay-- a sort of unique vanilla, coconut and hazelnut combination. We use a fairly high percentage of American oak on our Tempranillo to impart some of that traditional dill note that you get in many classic Riojas. And we tend to use light toasts for wines like our Grenache, and heavier toasts on the Cabernet Sauvignon. Ultimately, we utilize a variety of barrels from different forests and with different toast levels so we can craft the perfect final blend. We have over 20 types of barrels on site, which gives us a lot fo flexibility when it comes to matching wine to barrel.