Most of the most prized wines in the world are aged in wooden casks or oak barrels. Although there are other factors that determine the quality of wine, including the skills of the winemaker and the vineyard producing the grapes, the time spent in oak barrels will tremendously influence the ultimate character of the wine.
There are two primary reasons wine is aged in oak barrels instead of stainless steel tanks: The aging process enhances the aroma, flavor and complexity of the wine by extracting substances from the wood into the liquid. The oak allows oxygen to contact the wine, allowing a gradual process of oxidation to take place. There are several factors that the oak barrels add to the character of the wine, based on the type of wood being used, number of times the barrel has been used before, the technique used to create the barrel, the thickness of staves, the size of the barrel, the humidity of the cellar and the time the wine spends in contact with the wood. However, the one factor that causes the greatest disagreements between winemakers is the type of oak used in creating the barrels.
The variety of oak selected by the winemaker often depends on tradition, variety of wine, personal taste and economics. Due to its resilience, strength, workability and desirable effects on flavor and color, oak is the most common variety of wood used in aging wine. While redwood is commonly used to construct puncheons or uprights much larger than the traditional 60 gallon oak barrels, redwood is too rigid to allow staves to bend and can impart an undesirable flavor. Acacia, which was once common imparts a yellow tint to the finished product and has fallen out of favor. Chestnut, is high in tannin, which improves the flavor or the wine and prevents spoilage of reds is found too porous and thus must be coated with wax to slow wine loss due to evaporation.
On the other hand, oak barrels have a tight grain allowing a more gradual extraction of the desirable flavors and minimizing the loss of wine from evaporation. The wood is resilient, so staves can bend without breaking, high in tannin, durable, strong and offers a neutral wood smell, unlike some of the fruit woods. As a result, oak barrels have come to be used almost exclusively in the aging of finest wines.
Coopers, who make the barrels, pay higher prices for the wood, but demand higher quality than even fine furniture makers. As a result, oak barrels are usually expensive. However, oak barrels are not always appropriate for all varieties of wines. While many great wines, including those from Burgundy, Bordeaux and California may command a great enough price and require sufficient aging to justify the more expensive oak barrels, less expensive wines and those made with more delicate and lighter grape varieties, including Chenin blanc, white Zinfandel, Riesling, Gewurztraminer, some Sauvignon blanc and a few red grape varieties, including Gamay are bottle for consumption while still fruity and young. Aging such wines in oak barrels would reduice tehri fruity appeal and the cost could not be justified. Therefore, the wines are aged in stainless steel, using cool temperatures for a short period of time.