What's the difference between American oak and French oak for barrel-aged wines?

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Dear Dr. Vinny,
What is the difference between American and French oak for maturation?
—Steven M., Hong Kong
Dear Steven,
I like to refer to oak barrels as part of the metaphorical spice rack that vintners use to make a wine of their style. Barrels are made from oak trees grown all over the world, but the most popular barrels are made from oak trees grown in France or the United States.
Barrel-destined oak trees ideally grow in cool climates, which gives them a chance to mature slowly and develop a desirable tight grain. Most of the French oak for barrels comes from one of five forests, some of which were originally planted during Napoleonic times for shipbuilding. The main forests, mostly located in central France, are Allier, Limousin, Nevers, Tronçais and Vosges, and each is considered to have distinctive characteristics. When you order a barrel, you could very well specify from which forest you wish your barrel to be sourced.
On the other hand, American barrels aren’t typically distinguished by forest, and oak for barrels is grown in 18 different states, mostly in the Midwest and in the Appalachians, as well as Oregon. It’s estimated that the 5.2 billion white oak trees in the U.S. cover a total of about 235,000 square miles.
Keep in mind that there are a lot of variables when it comes to oak aging. Some producers use exclusively French or American barrels, while others mix it up. Even if a producer uses exclusively French or exclusively American barrels, there are other variables, such as different barrel producers, different levels of toast (the heating of the inside of the barrels), and mixing newer (and therefore stronger) with older (more neutral) barrels. Some winemakers might barrel-age their wines for only a few months, while others can go a couple of years or more.
Speaking in broad generalities, French oak barrels are typically more subtle and spicy, offering textures of satin or silk. American barrels tend to be stronger in flavor, often described as cream soda, vanilla, or coconut, resulting in wines with a more creamy texture.
—Dr. Vinny