Why char whiskey barrels

See our FAQs for additional Covid information. After all, aging in a charred oak barrel is one of the legal requirements for bourbon. So why do we do it? People have suggested that the inside of barrels were originally burnt to remove the leftover flavors of goods previously stored within, which sounds reasonable enough.

So why do barrel coopers still char the interior? First off, charring essentially opens the wood up, making it easier for bourbon to extract flavors. It also catalyzes key chemical changes that are essential to bourbon. And while the purpose of charring seems sort of intuitive—a charred surface yields a smoky flavor, right? And delicious. In fact, smoke is one of the lesser goals of charring.

Rather, charring is done to change the nature of the oak itself, to yield the best possible reaction between wood and whiskey. They may stand weirdly still outside of Entwood, but trees actually have a lot going on in them. Again, fortunately, whiskey barrel science is concerned with a small group of compounds.

And the extent to which you char a barrel will have an impact on those last four. The hemicellulose is one of the most important components of American oak. The more a barrel is charred, the more the lignin yields flavors of spice and smoke. Within that requirement, however, there are myriad variations that can affect the color, aroma, flavor, and mouthfeel of the final whiskey.

Working within those barrel specifications allows distillers to craft a distinctive product, with decisions about char and toast level having major ramifications on the final whiskey. Wood terroir is one variable. While more or less all barrels are made of white oak, the wood itself can vary by region.

In colder northern climates, for example, trees grow more slowly and have a tighter grain. The flavors they offer are more concentrated, but also harder to reach and absorb. After the wood is harvested it must be dried, or seasoned, since more than half its weight is water. Kilning —drying the wood in a heated chamber—is the fastest and easiest way, but not the best.

With natural seasoning, rough-cut staves and headpieces are stacked up outdoors and left alone for six to 24 months occasionally longer. They are rained and snowed on, baked in the sun, frozen, thawed, and invaded by microbes.

This process reduces tannin levels and breaks down various compounds, which are then available for incorporation into the whiskey as it matures. Natural seasoning allows the wood to begin decomposition, which is good. Fungi send out roots hyphae that penetrate into the wood structure and release hydrogen peroxide, a natural bleaching and oxidizing agent that helps break the wood down chemically, softening tannins and caramelizing hemicellulose a complex carbohydrate found in plant cells , among other salutary effects.

Kilning does none of that.