Oak, also known as the winemakers spice cabinet. It affects wine not only the flavor of wine but its chemistry as well. It is important to understand that not all oak is the same.
Different Oaks for Different Folks
I’m sorry I couldn’t resist that. It is true though. Oak from different countries impart different flavors and textures to the wine it comes in contact with. This is why you see French and American barrels and oak chips at wine making shops.
The two most popular types are French and American, however, there are many other places that supply winemakers as well. Hungary is one of the more popular ones outside the U.S. and France.
French oak is more tame and subtle while American oak, like Americans, tend to be pretty bold. To be more specific, French oak has a finer grain with smaller voids (air space). This keeps the wine from penetrating very deeply into the oak thus reducing the surface area that the wine has contact with. This results in a smoother, subtle oak flavor.
American oak, on the other hand has a looser grain that allows more interaction with the wine as it can penetrate deeper into that grain. Increased surface area allows for more extraction of flavors and tannins from the oak.
Here are the four main impacts oak can have on wine. As you’ll see oak flavor is only one of the four.
Evaporation
The average 59 gallon barrel allows 5.5-6.5 gallons of wine evaporate per year. This is why wineries have to top up their barrels so much and why they smell so good! As wine evaporates is the water and alcohol that are lost, this concentrates the flavors and aromas.
The water and alcohol that is lost is replaced with additional wine which introduces more flavor and aroma compounds. You can see how this would add up, especially for a red wine that is barrel aged for three years.
Micro-Oxygenation
This is a big one. Just as the barrels allow water and alcohol to evaporate out of the barrel, oxygen is also allowed in. However, only in very small quantities.
While too much oxygen is obviously a bad thing the tiny amounts gained through micro-oxygenation is just enough to help the wine mature. Without this additional oxygen the wine can still mature, however, it takes much, much, longer to achieve similar results.
Phenol Interaction
Phenols are compounds found in the grape and the oak that make up the flavor, aroma, and mouthfeel of a wine. There are hundreds of different phenols in a typical wine. Most come from the grapes but oak can also impart some of its own. These phenols can combine to form new flavor and aroma compounds.
One common compound created is vanillin which, as you might have guessed, gives wines a vanilla flavor. Fermenting wine in the barrel, or with oak chips, can also give rise to new compounds or at least modified compounds. As the yeast work their magic they process phenols from the grape juice and the oak, combining them to form new compounds, i.e. new flavors and aromas that weren’t there before.
Tannins and Flavor
Oak imparts both tannins and straight up oak flavor to wines aged in barrels newer than 5 years old. This is probably the most important use of oak aging. Red wines without oak just aren’t the same. Chardonnay can be quite good without it but I’ve yet to come across an un-oaked Zinfandel. There’s a reason for that.
The flavor profile that the oak imparts on wine can be played with by using oak that has been toasted to different levels. Toasting is a necessary process which makes the staves flexible enough to bend them into the final barrel shape we’re accustomed to.
During this process the wood is charred slightly, as you might imagine. Lightly toasted oak imparts more green or unripe flavors. A heavy toast is known to produce vanilla, mocha, and caramel flavors. The four common levels are light, medium, medium plus, and heavy.
American Oak Photo by: Jeffery Turner
Oak Barrel Dining Room by: John