One rule, three styles
America's defining rule: bourbon and rye must age in brand-new charred oak. New wood works fast and loud — caramel, vanilla, toasted spice — which is why American whiskey tastes bold at ages that would be adolescent in Scotland. Bourbon leads with corn sweetness; rye with pepper and herbs; Tennessee adds charcoal-mellowing for extra polish.
The used barrels don't go to waste — they sail to Scotland and Ireland, where 'ex-bourbon' casks raise most of the world's malt whisky.