WHAT OAK DOES

Without oak, many wines as we know them would not exist. They would not taste the same, smell the same, or have the same texture. Nor are there substitutes for oak. Cherry, walnut, chestnut, pine, and many other woods can all be made into barrels; none, however, enhances wine the way oak does. Nor has technology devised an oak alternative. In short, wine and oak-inseparable for the last two millennia of winemaking-show every sign of remaining married. Why is there a special affinity between oak and wine? Oak has the ability to transform wine, to coax it out of the genre of simple fermented fruit juice and give it depth, length, complexity, and intensity.

Oak wood is composed of several classes of complex chemical compounds, which also leave their mark on a wine's aroma, flavor, and texture. The most noticeable of these are phenols, some of which impart vanilla-like flavors, notes of tea and tobacco, and impressions of sweetness. One of the most important classes of phenols is the substances commonly called tannin.

The impact oak has on wine depends, among other things, on th type of oak used and the way the barrel was made.

Of the four hundred species of oak trees that grow around the world, three main types are used in winemaking: the American oak Quercus alba (mainly from the Midwest) and the French oaks Quercus robur and Quercus sessiliflora (from central and  eastern France). The flavor American oak imparts to wine is quite different from the flavor French oak imparts to wine; American oak tends to be more pronounced and vanillin; French oak, more subtle. Neither is necessarily better than the other in the same way the basil isn't necessarily better than rosemary. The idea is to find a type of oak that will best show off the fruit flavors in a given wine. To determine this, winemakers age small lots of their wines in several different oaks from different forests and a variety of coopers in both countries and then see which ones work best.

A winemaker can choose to put a wine into new barrels, used barrels, or a combination of new and used barrels. Although the extraction rate of vanilla and oak flavors differs based on tile grain of the wood, most barrels impart little flavor after four to six years of use. Also, some wines leave layers of natural deposits on the insides of the barrels, which, over time, shield a wine from any wood contact whatsoever.