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Why Oak Barrels?
Why Oak is Used for Wine Aging

Doug Badenoch, owner of the Wine Gallery in Bozeman, Montana, ran this in his newsletter last week and when he asked to adapt our "We Join a Wine Club" article from last week, I offered to trade.


Oak barrels costing over $1,200 apiece may be the second largest expense for most wineries after the grapes. Mass produced wines may get their oak influences from oak chips or staves inserted in stainless steel tanks, but most of the fine wine producers, define this as those who will take you on a tour, depend on barrels.

Wine and oak are a marriage made in heaven. Most medium to heavy bodied wines (both white and red) benefit from some contact with oak barrels. Oak is used as a spice to enhance the flavors and impart character to the fermented fruit.

Making oak barrels is a complicated process. Of the 400 odd species of oak, less than ten species are used to make oak barrels for wine. The ideal oak tree is over 100 years old, and has lived in a cool, dry forest. Cool and dry results in slower growth with grain or growth rings that are closer and tighter. As a result, the tannins are more evenly distributed and mellower when the oak comes into contact with wine.

After the tree has been harvested, the wood is hand split along the natural grain lines making the rough barrel staves. These staves are seasoned for 2-3 years outdoors in the sun, rain and wind. During this period, the harsh tannins are leached out and the mellower, soft tannins remain.

To make the barrel, the staves must be shaved so they fit as closely as possible. Any gaps in the staves would allow air to enter and wine to leak out. The barrel is formed over an open fire to make the staves more pliable and iron rings are hammered into place to hold the barrel together. The fire also caramelizes some of the wood's natural sugar into toasty, spicy, vanilla flavors. These flavors are ultimately imparted to the wine.

Oak barrels make wine softer and mellower through a couple of processes. One is the permeability of oak. Wine evaporates out of the barrel and oxygen seeps in. The slow oxidation of wine mellows the grape tannins and softens the hard edges. The interaction of the yeast and the wood is also important to the maturation of the wine.

Oak contains several organic chemical compounds which leave their mark on the flavor, aroma and texture of wine. Tannins in oak impart vanilla, tea, tobacco and even notes of sweetness. New barrels impart stronger flavors and used barrels contribute more subtle nuances.

Winemakers have many choices when it comes to barrels. American oak barrels impart a stronger wood flavor and more vanilla. French oak barrels impart more of the sweet spices of cinnamon and nutmeg. Some barrels receive toastier flavor from longer exposure to fire during the barrel-making process and toast may be more appropriate for certain white wines. In addition, winemakers can age wine in new barrels, used barrels or a combination of new and used to achieve the proper seasoning for the wine they make.

Barrels can vary in size but most hold about 60 gallons (~225 liters). Hogshead are slightly larger at 80 gallons (300 liters) and are used when winemakers want less oak suffused into more delicate reds like Sangiovese and Pinot Noir.