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  • Barrell Craft Spirits



We all know what makes a great bourbon: A deep amber color, richly aromatic aromas, and that iconic flavor that melds caramel, vanilla, baking spice, and fruit into a spirit that’s far more than the sum of its parts.

The process of making that spirit? Not so straightforward. Read on for a crash course in the rules governing bourbon, and to find out why oak might be bourbon’s most important ingredient at all.


Bourbon is one type of whiskey specific to the United States. In other words, all bourbon is whiskey, but not all whiskey is bourbon.

Among bourbon’s many special attributes, it must be made from a mash of at least 51% corn, distilled to no higher than 160 proof (80% alcohol), filled into cask at no higher than 125 proof (62.5% alcohol), and bottled at no less than 80 proof, or 40% alcohol by volume. Straight bourbon, an important sub-category, has to be at least two years old and contain no additives of any kind. Oh, and it’s all gotta be made entirely in the United States.

Perhaps most importantly of all, bourbon can’t be filled into just any barrel. Like the special snowflake it is, bourbon requires a very specific kind of whiskey barrel for its aging process.

Picky? Yes. But bourbon isn’t just any whiskey.


Bourbon must be aged in new, charred oak barrels. It’s a critical step in developing bourbon’s distinct flavor.

Freshly distilled bourbon doesn’t look anything like what you use to make an Old Fashioned. When it comes out of the still, it’s crystal clear, and smells and tastes like funky raw grain. Most of a bourbon’s character, and all of its color, come from the cask itself.

As the bourbon ages in the barrel, it soaks up flavor, aroma, and pigment from the oak. All barrels used to age beverages are heat-treated in some way, since raw wood has an unpleasantly green and sappy flavor. Wine barrels are usually toasted, while bourbon barrels are always charred, giving them a sweet, smoky tinge.

You can think of casks a little bit like tea bags. They’ll always impart the most flavor on their first use. You can use them a second, third, or even fourth time, but with every use, they lose a little bit of their flavoring power.

Bourbon regulations require the use of brand-new barrels each and every time, which means bourbon usually has a robustly oak-driven flavor profile. Key oak flavor attributes are vanilla, baking spice, caramel, and coconut.

Most bourbon is aged in barrels made from American white oak, but any type of oak is allowed. What’s definitely not allowed is re-using those barrels to age more bourbon.

That’s not to say those barrels don’t get reused at all. Distillers around the world rely on Kentucky bourbon distillers and their seemingly endless stream of once-used barrels as a reliable source for casks to age Scotch whisky, Irish whiskey, rum, and aged tequila. There’s still plenty of oomph left in those casks to age other spirits–just not enough to create that unmistakably oak-driven character of American bourbon.

Ready to taste some of that oaky goodness for yourself? Visit Barrell Craft Spirits’ website to shop our bourbons, ryes, and whiskeys online, or use our map tool to find a retailer near you.


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