What's the difference between a toasted barrel and a charred barrel?

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Dear Dr. Vinny,
What's the difference between a toasted barrel and a charred barrel?
—Chris, Boston
Dear Chris,
During barrel production, the insides of barrels are typically toasted—either over an open flame or over an oven. Toasting both mellows the tannins in the wood, as well as changes the flavors the barrel might impart from raw wood to more spicy, vanilla notes—toasting actually helps release vanillin from the cellulose in the wood. There are varying degrees of toasting—from a light toast to a heavy toast and, as you might imagine, that changes the way they can influence a wine. Essentially, the heavier the toast, the stronger the barrel’s flavors.
The word “charred” implies that something has gone past toasting to partially burning, and indeed charred barrels look black inside—they are about an eighth of an inch charred. Charred barrels aren’t really used for wine, but they are a part of bourbon production. That charred wood ends up becoming a sort of activated carbon filter, which can help remove sulfur compounds from a whisky, and make a smoother drink. Charred barrels also impart a darker color, smoky notes as well as caramel, honey and plenty of spicy accents.
—Dr. Vinny