There is an analogy in wine making that goes something like this: aging wine in an oak barrel, is like seasoning stew in a pot.
Before wine is racked into a barrel, it is just wine. After it has been in oak for a specified time, a new wine is transformed that is no longer just wine, but now something different because of its exposure to the oak. (Throughout this essay, the only wood mentioned will be oak, although there are other woods used in wine making, like chestnut).
There are many different types of oak, but just two botanical geniuses or Quercus: two European and one American that are the overwhelming choices for wine making. European oaks used mainly in wine making are Quercus robur (aka French oak) and Quercus petraea.
The majority of American oak used in wine making is Quercus alba. Oregon winemakers have been experimenting with a white oak, Quercus garryana.
There is no hard and fast rule saying that any type of wine must be fermented or aged in any type of oak. While there is some general agreement which pairing works best, winemakers are free to experiment. In the early 1990s, Napa Valley Chardonnay was aged in French oak (and still is), but the folks at ZD Wines thought their Chardonnay tasted better after a period in American oak.
Although there are no records that Bordeaux red and white wine were ever aged in anything but French oak, winemakers in other regions discovered that certain oaks marry better with specific wines. Chardonnay, for instance, is thought to be better with less assertive French oak than more aggressive and tannic American oak. On the other hand, American oak seems better suited to tame the strong tannins of Zinfandel.
Another factor in deciding what oak to use was the availability of local wood. For years, some Italian winemakers used locally-grown chestnut, Chilean wines were aged in rauli (a type of evergreen beech) and California wines were matured in redwood tanks. Local woods were used because that was what grew near the winery and was the most economical.
Of course, there is also the botanical makeup of oak trees to consider in wine making and the aging of wine in oak. Mostly it has to do with the physical characteristics, such as tight grain or loose grain, which determine the practical necessity of sawing or splitting the oak into lengths that will become staves.
The trunk of an oak tree is made up of bundles of tubes, blocked by tyloses. The more tyloses and tubes the more water tight the barrel. American oak has many tyloses, thus it can be sawn, while French oak is deficient in tyloses, requiring a cooper to split the oak.
The flavors in wine derived from contact with oak is a complex subject involving a lot of chemical substances. What follows are general comments describing the three main flavoring compounds in oak.
Lactones are compounds, higher in American oak than in French oak, that provide a coconut flavor. Toasting, or charring the inside of the barrel brings out earthy and spicy notes.
Aldehydes provide the vanillan (vanilla) compound, found to be higher in American oak than French oak.
Phenols provide aromatic elements, from clove to lightly smoky.
Other contributors include terpenes (perfume), carbohydrates and tannins, compounds found in some oaks. In a broad sense, then, vanilla and coconut are associated more with American oak, while spice is more common in French oak.
The Rise of American Oak
Years ago, American white oak, grown mainly in the Midwest, was used mostly for whiskey barrels. Large cooperages turned out thousands of barrels, on a sort of assembly line, that were sold to Bourbon distilleries. American oak for wine use was then mostly unheard of.
As the demand from wineries, mainly in California, grew for American oak barrels, large cooperages, like Canton, devoted a small part of their vast space to making wine barrels, mainly by hand, a process known as "raising a barrel." Seeing a chance to get into a growing business, French cooperages such as Seguin Moreau established cooperages in California wine country.
There is so much more to be said about the close association of oak and wine, such as how the barrels are made, how the wine is made, how long the wine stays in contact with the oak, the age of the barrel and how many times it has been used and more.
The bottom line is, like anything else, too much oak can spoil the wine. But careful use with just the right type of oak, and the marriage is harmonious.
Next blog: Chardonnay Styles
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