Oak (wine)

Lore & Background

In early wine history, the amphora was the vessel of choice for storage and transportation. The Greek historian Herodotus noted that ancient Mesopotamians used barrels made of palm wood to transport wine along the Euphrates. Palm is difficult to bend and fashion into barrels, and wine merchants experimented with different wood styles. The use of oak has been prevalent for at least two millennia, first coming into widespread use during the time of the Roman Empire. Winemakers discovered that wine kept in oak barrels took on properties that improved it by making it softer and, in some cases, better-tasting.

The porous nature of an oak barrel allows evaporation and oxygenation without causing oxidation or spoilage. The typical 59-gallon barrel can lose 5 to 6 gallons per year, concentrating flavor and aroma compounds. Small amounts of oxygen soften the wine's tannins. Phenols within the wood interact to produce vanilla-type flavors and can give the impression of tea notes or sweetness. The degree of 'toast' on the barrel affects tannin levels and wood flavors. Hydrolyzable tannins known as ellagitannins help protect the wine from oxidation and reduction.

White wines fermented in oak have a pale color and extra silky texture; those fermented in steel and matured in oak have a darker coloring due to heavy phenolic compounds. Flavor notes commonly associated with oak include caramel, cream, smoke, spice, and vanilla. Chardonnay fermented in oak can show coconut, cinnamon, and clove notes. The 'toastiness' of the barrel can bring out mocha and toffee notes in red wine. It is a common misconception that oak imparts butter flavors; butter flavors come from diacetyl produced during malolactic fermentation.

Reader's Guide

Oak's significance in winemaking lies in its ability to modify wine structure and flavor through controlled exposure. The length of time a wine spends in the barrel depends on the varietal and desired style. Most oak flavoring is imparted in the first few months, while longer exposure adds light aeration that precipitates phenolic compounds and quickens aging. New World Pinot noir may spend less than a year in oak; premium Cabernet Sauvignon may spend two years; the very tannic Nebbiolo grape may spend four or more years. High-end Rioja producers sometimes age wines up to ten years in American oak for an earthy cedar and herbal character.

Different oak species and sources produce distinct effects. American oak (Quercus alba) is characterized by fast growth, wider grains, and lower wood tannins, and tends to be more intensely flavored with sweet and vanilla overtones due to two to four times as many lactones. French oak (Quercus petraea and Quercus robur) is valued for finer grain and richer aromatic components. Italian winemakers have long used Slavonian oak (Quercus robur) for its tight grain, low aromatics, and medium tannins. Hungarian oak (Quercus petraea) from the Zemplén Mountains is known for fine tight grain and delicate extraction, conveying toasted, vanilla, sugary, woody, spicy, and caramel-like flavors with less intensity and more slowly than American or French oak. Russian oak from the Adygey region is explored as a cheaper alternative. Canadian oak is described as a middle ground between American and French oak.

Did You Know?

• The typical 59-gallon oak barrel can lose 5 to 6 gallons per year through evaporation.
• American oak has two to four times as many lactones as French oak, giving more sweet and vanilla overtones.
• Oak trees are typically harvested in winter when there is less sap in the trunk.
• It is a common misconception that oak imparts butter flavors; butter notes come from diacetyl during malolactic fermentation.