What's the difference between French and American oak barrels?

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Dear Dr. Vinny,
What is the difference between French oak barrels and American oak barrels?
—Russ B., Cottonwood, Ariz.
Dear Russ,
The first difference is pretty obvious: French barrels are made from oak trees grown in France, and American barrels are made from oak trees grown in the United States. To be more specific, the two species of oak trees mainly used for barrels in France are Quercus robur and Quercus sessiliflora, while in America, the oak typically used is Quercus alba. Speaking in broad strokes, French oak barrels are know for giving wine more subtle and spicy notes, with silkier textures. American barrels tend to be more potent in their flavor, often described as giving notes of vanilla, cream soda and coconut, with a creamier texture.
That said, a lot of variables can affect how a barrel influences a wine. There are different barrel producers and different levels of “toast,” which refers to heating the inside of the barrel to char the wood. The influence also depends on how the barrels are used. Some wines are aged in barrels for a few months, others for a few years. Newer barrels are stronger, while older barrels are more neutral. Plenty of winemakers use a variety of barrels, including a mix of French and American, or barrels from other sources, such as Hungary and Slavonia.
—Dr. Vinny