There are five rules that make bourbon authentic, and they are codified by the United States Alcohol Tax and Trade Bureau. One particularly unique law that defines authentic bourbon’s flavors is that the spirit must be aged in charred, new oak containers, and while this law is very strict, it's not as specific as you may think.

Alcohol cannot qualify as bourbon if it's not aged in charred new oak, but there’s no distinction about what kind of oak to use, and while we tend to call aging containers "barrels," the law doesn't specify that the vessels have to be barrels. Charred new oak is all that's required to create bourbon's sweet caramel and vanilla notes.

The tradition and resulting law of new oak barrels likely dates back to when bourbon was first produced in Kentucky, when oak trees were abundant in the state. American white oak trees are currently growing on over 100 million acres of land, but even that isn't enough to keep up with the growing demand for the beverage today.