Wood and Wine

the how and why of aging wine in wood

How wine came to be aged in wood was, as many human inventions are, a happy accident. Rather than being containers for fermenting wine, wooden barrels first served as vessels to transport wine. People came to realize that by the time the wine arrived at its destination something had changed—the wine had gained a softer taste and different aromatics. They liked the wine better, and thus they started intentionally aging wine in wood, rather than the clay pots used before.

Many chemical processes occur when a wine ages in barrel, many of which are not completely understood, though most of the changes happen due to the interaction of wood and fermenting wine. Oak—whether French, American or Slavonian—is the predominant kind of wood used in winemaking, because it’s strong, relatively easy to cut and watertight. Oak also has the ability to transfer flavor and influence the structure of the wine. Although the different regions’ oaks may seem the same, there are huge differences in these woods. Not only do different woods require different barrel construction, but they also affect the resulting wine differently.

To make the barrels, the wood has to be split or sawn into staves. Out of all the oaks, French oak is the hardest to work with. The oak must be split in order to be watertight, while American Oak can simply be sawed into staves—French oak’s increased labor adds to the premium paid on it. After being split or sawn, the oak is seasoned, or dried out, for about two to three years; this decreases many of the wood’s bitter and acidic components. Drying can be done in ovens too, but this is a cheap way to circumvent the long delay, and the resulting wood is lower in quality. Depending on the specifications of the winery, the barrels can also be toasted by the cooper. The staves must be bent into shape using heat, which often chars the inside of the barrel imparting a more pronounced flavor. There are varying degrees of toasting, but it is always important that balance is met between the wood and wine.

There are distinct differences in the flavor and aromatic profiles of each type of oak. American oak imparts more oaky flavors like butterscotch, vanilla, caramel and coconut because of the higher porosity of the wood. French oak has a more elegant expression on its wines and lends a very balanced creaminess, vanilla and spice to the profile. Slavonian oak is very tight and tends to only impart some spice.

In addition to the type of oak used in a barrel, the size of the barrel also plays a huge factor in a wine’s elevage. Small barrels (225 liters) have much higher surface-area-to-volume ratio; thus, the effects of the oak are more pronounced. In large casks containing up 1000 liters, the effect is much less pronounced due to the lower surface-area-to-volume ratio. Either method can produce world-class wines; it’s really up to the producer to make the decision. As long as the wine has balance, either method works.

Here you can see larger Slavonian Oak in the background and smaller French barriques in the foreground.

Perhaps even more than adding oak’s flavor, the most important reason for using barrels is micro-oxygenation. Although watertight, barrels are not air tight. Small amounts of oxygen permeate the barrels, which in turn oxidize the wine. This minute oxidation is beneficial because the tannins essentially bind to the oxygen, causing precipitation of some tannins and yielding a more rounded wine at inception. Tannins contained in the wood itself also leach into the wine, adding structure and flavor.

While this explanation is by no means exhaustive, I hope you learned a bit about the tight relationship between wood and wine. You don’t need the former to make the latter—just look at Josko Gravner and his amphora—but it helps. And now you know a little bit about why.