How Barrel-Aging Works

Aging spirits are part and parcel of many of your favorite liquors. From rum to bourbon, tequila to scotch, barrel-aging is part of the spirits culture and process. A happy by-product of all this barrel-aging is, surprise, excess barrels! These barrels often find a second life with brewers and other distillers. And, because of the wide variety, brewers can create truly unique offerings.

As our program has become more and more popular, we thought it would be helpful to understand more about how the process works, the considerations and what to look for. This isn’t going to be heavy science about lactones and phenols, but more of a “friendly” way to understand barrel aging.


Why’s it done in the first place?
There is an underlying assumption about barrel-aging that just glosses over the reasons in the first place- it’s what you do. But there are two fundamental reasons to barrel-age spirits.

First, the filtering process that occurs takes out the harsh notes of distilled spirits. Think moonshine… that’s the way most spirits start. They are very strong, with sharp edges. Desirable in some places, but not others. Secondly, the barrel itself will infuse the spirit with flavors, color and tone. Different barrels will react different, but all of them contribute to the overall flavor effect.

Different wood, different flavor
Chances are, the barrel you meet in the US, particularly the south, will be American Oak. The reason is simple: For bourbon to be called bourbon, it must be aged in an American Oak barrel. And, given our region, we have an ample supply of bourbon distilleries to collect from. While European Oak is known for spice with vanilla flavors, American Oak is known for it’s caramel with vanilla tones.

What does the char do?
Many, not all, barrels are charred of toasted. And both treatments do much of the same, adding charcoal to the inner lining of the barrel. Odds are, in the US you will encounter charred barrels, as it is the prevailing style. The char caramelizes the sugars in the wood, producing the signature flavors you can recognize in an aged spirit as the fluid passes through. The char really matters, and bourbon distillers will perfect their proprietary styles.

But just as important, the char helps to filter out undesirable chemicals; those that occur naturally through the distillation process. The carbon wall is much like a filter pad you’d see in an aquarium. It helps to purify the alcohol as it passes into and out of the wood.

Temperature fluctuations matter
As temperatures vary, the wood barrel will absorb the alcohol differently. In warmer weather, the wood will become saturated, while in cooler weather, the wood will squeeze the alcohol out. Consider the bourbon belt… why Kentucky and Tennessee? They’re not really known for corn and grains. If it were based on harvest availability, Indiana would be a great place. Rather, these regions have deeply varied seasonal differences (in addition to forestry, nearby).

The hot summers and cold winters help the spirit move in and out of the wood, picking up flavor and filtering our undesirable chemistry all year long. It’s one of the reasons Scotch ages so long. With the cooler climate, it takes far longer to barrel-age the spirit to the desired result.

Second lives for bourbon barrels
For bourbon to be called bourbon, it must be aged in a new, charred American Oak barrel. As such, there is a wealth of barrels that can no longer be used to make bourbon. They offer brewers and manufacturers a deep, rich resource of experimental material. They show up in unusual places - vinegar, syrup, wines, as well as other spirits.

In all cases, the freshly used barrel brings along the notes of the bourbon as well as the caramel and vanilla of the oak. With the char still doing its job, anything aged in a bourbon barrel will have its harshest notes smoothed, leaving a mellower version of the fluid.

A barrel may be used and reused many times over as it continues its lifecycle. As long as the barrel doesn’t dry out, which can cause leaks. Older barrels may need to be cured, but a barrel filled simply with water will remain tight and effective.

Learn more about it…
If you’re really interested in learning the science behind barrel-aging, do some research. Most distilleries have information on their sites about their process and there is ample information from third parties. You can always as our bartenders or speak to one of the head brewers. As our program builds, we will try to keep you informed about the pedigree of a barrel and what you could expect it to do.