Most of the world’s fine wines are aged in wooden casks or barrels. While there are other determinants of a wine’s quality, such as the vineyard and the skill of the winemaker, the period of up to several years in wooden “cooperage” or barrels has a significant influence on the ultimate character of the wine.
Wine is aged in wooden barrels, as opposed to stainless steel tanks, to enhance the flavour, aroma and complexity of the wine through the extraction of substances from the wood into the wine, and to allow air (oxygen) to come in contact with the wine to allow a slow, gradual oxidation process. The influence of barrel aging on the character of a wine varies based on several factors, including the type of wood used, the age of the barrel, the techniques used to make the barrel, barrel size, thickness of the staves (the individual strips of wood which form the barrel), cellar humidity and the length of aging.
Why Oak?
Oak, on the other hand, due to its strength, workability and lack of undesirable flavour or colour extractives, is used almost exclusively in the barrel aging of fine wines. Oak has a relatively tight grain which permits a more gradual extraction of wood flavours and minimizes wine loss through evaporation. It also is resilient, enabling staves to be bent without breaking and unlike other hardwoods such as apple or cherry, has a neutral wood smell. Oak is high in tannin, which in proper amounts is an important flavour component as well as allowing red wines to age by gobbling up oxygen, which would otherwise spoil the wine.
French vs American Oak
There is a difference of opinion between the majority of winemakers who insist on French oak and the growing minority using American oak. In the United States, white oak, grown in Virginia, Missouri, Kentucky, Oregon, and Ohio, is the species used for barrels. It is preferred over red and black oak due to its tighter grain which minimizes evaporation of wine from the barrel and its resistance to shrinkage after wine is removed, an important feature in preventing wine from leaking out of a newly-filled barrel, and its high tannin content.
French white oak is harvested from several different forests in France. The most common forests are Limousin, Alliers, Vosges, Troncais and Nevers, each producing oak that imparts slightly different nuances of flavour to the wine. The tightness of the grain, which determines the rate of extraction of these flavours, also varies among forests. Winemakers typically use a blend of barrels from different forests to take advantage of the unique characteristics of each. This notion of regional character does not exist with American oak. Winemakers using American oak are more concerned with the reputation of the cooper than exactly which state the oak was grown in.
As wineries have sought to lower production costs, the demand for American oak has increased dramatically. More winemakers have substituted American oak barrels costing about $200 each for French oak barrels costing over $500 each. This trend has prompted renewed scrutiny of the differences between American and French oak.
While both American and French oak contribute tannin and aroma, French oak contains more tannin and flavour components and has a less obviously “oaky” flavour and smell than American oak. American oak has a more aggressive mouth-feel and immediately apparent aroma. American oak contains more vanillin (vanilla aroma) and more odorous compounds.
It was thought American oak’s somewhat harsh, raw character ruled out its use for white wine and made it desirable for aging powerful, robust red wines such as Zinfandel, Cabernet Sauvignon, Merlot and Petite Syrah. But coopers in California have been successful in reducing the undesirable characteristics of American oak by applying production techniques traditionally used by French coopers. For example, the newly cut stave wood is stacked outside to air-dry for a minimum of 18 months instead of the more expedient kiln or oven drying. Air-drying exposes the wood to periods of rain and drying which leach out excessive harshness while retaining desirable components such as vanillin, 70% of which is lost during artificial drying. And “toasting” of the barrels is carried out more slowly over a lower heat, allowing a deeper penetration of the flame. In the past, American oak barrels were flash-fired, resulting in a heavy char suitable for aging bourbon.
Differences of Opinion
Despite the progress in making American oak barrels more appealing, some winemakers remain adamantly opposed to its use in any form, particularly for white wines. American oak gives us what we want. If American oak has gotten a bad rap it could be because the low price makes people think it is low quality before even trying it. In fact, American barrels in the past may not have been suited to wine. They were originally air-dried for one year and given a heavy char to age whiskey in. As such, they were inappropriate for wine storage.”
Some opine that American oak flavours are flashier and more upfront and fade after a few years instead of developing like French oak. The air-drying of American oaks may leach out excessive tannins, but does not change the nature of the extract. The debate over French versus American oak is a lively one; it would be an oversimplification, however, to limit the oak question to the choice between American and French oak. Other factors, such as the cooper, toast levels; grain, cellar conditions and length of aging all have an important influence on the wine.
