You don’t have to be a whiskey expert to know that barrel aging is an absolutely essential part of the modern production process. But you may not be aware that the earliest whiskey drinkers took it straight from the still. In fact, this practice went on for centuries until an accident of history changed the game forever.

Spanish sherry was all the rage among the French aristocracy in the 1800’s, and it wasn’t long before those empty sherry casks started to pile up. Scottish distillers in need of shipping solutions started buying up the empty barrels, and unknowingly ushered in a new dawn for whiskey production.

Soon enough, distillers began to notice that the longer the whiskey spent in barrels, the richer the flavor and color became. And the rest, as they say, is history.

So the next time you’re sipping on your favorite whiskey, take a moment to appreciate the clever Scottish distillers who brought that one-of-a-kind taste to life. And in the meantime, brush up on your knowledge of the barrel-aging process.

The types of barrels are important

First, an important distinction. All barrels are casks, but not all casks are barrels. A “barrel” is a large cask (usually 50-53 gallons). Most whiskey barrels are made of white oak, which is a strong, moldable wood found throughout North America and Europe.

The tree’s place of origin affects the way flavors are imparted during the aging process. Wood from colder climates, where trees grow more slowly, have a tighter wood grain and more concentrated flavors that take longer for the spirit to absorb.

The typical steps of the barrel aging process

• Seasoning: After it’s harvested, the wood is dried, or “seasoned.” The process can be done quickly in a kiln, but most whiskey producers opt to let the wood dry outside. There, it is exposed to the elements for six to 24 months. The process of natural decomposition begins, and fungi helps soften tannins and break down the wood in preparation for barrel aging.
• Charring: Once it’s been seasoned, the wood is shaped into barrels and the interiors charred with open flames of up to 600°F. Distilleries make individual decisions about how long to char the barrels (anywhere from a few seconds to a few minutes). The higher the char level, the more the spirit will seep into the pores of the oak once in the barrel.
• Toasting: Some distillers also choose to toast (think “bake”) their barrels. The toasting process caramelizes the wood sugars and produces vanilla and caramel notes. “If you pre-toast the wood, you can better control your vanillin, your vanilla, and your color,” according to Master Distiller Chris Morris.
• Maturation: Once the barrels are ready, they’re filled with the raw spirit and stored in warehouses (or “rackhouses” as they’re often called in the U.S.) The temperature and humidity levels of the barrel storage location affect the final characteristics of the whiskey.  Barrels can be reused (typically no more than three or four times), and distillers take into account the previous contents when strategizing the new spirit’s desired flavor profile.

A bit of barrel science

While lay people like us rely on distillers to manage the science behind barrel aging, it’s not a bad idea to get a handle on a few of the finer points.

Don Livermore, master blender for Canada’s Hiram Walker and Sons, compares the three main compounds in wood to a brick wall. According to Livermore, cellulose and hemicellulose are the bricks, and lignin is the mortar.

“Cellulose and hemicellulose will contribute caramel, toffee, nutty, maple, cardboard or cotton candy notes to whiskey, whereas lignin contributes vanilla, smoky, leather, spice, creamy or medicinal flavors,” says Livermore.

Another important point to remember is that although barrels appear solid, they do allow airflow—gradually inviting oxygen into the aging process while allowing evaporation to take place.  

Why barrel aging matters in whiskey production

The importance of aging whiskey in barrels can be distilled (couldn’t help it) down to three main points: flavor, color, and filtration.  

Flavor: Experts say 60-80 percent of a whiskey’s taste comes from the barrel. That’s why distillers pay such close attention to the type of wood, age, size and previous liquid in the barrel.

American white oak often produces a sweet taste with notes of vanilla and caramel, which is a typical bourbon flavor. European oak has a spicy taste and stronger wood notes. Charring contributes to flavor by removing tannins and deepening the flavor of sweet-tasting compounds like vanillin.

As you might imagine, whiskey stored in a new cask absorbs the most flavor from the wood. (By law bourbon must be aged in a new cask.)

Color: Whiskey gets 100 percent of its color from the barrel. As changing temperatures move the whiskey in and out of the porous wood, the alcohol draws out pigmentation that gives it that signature color. Typically, the longer it stays in the barrel, the darker in color the whiskey becomes.

Filtration: The char on the inside of a barrel filters out chemical impurities that affect the final taste and quality of the whiskey. This process helps the flavor evolve from a harsh “moonshine” taste to the smooth, mouth-watering goodness of a fine whiskey.

So let’s raise a glass to barrel aging, the happiest of historical accidents. If you’re interested in taking your whiskey journey to the next level, check out our exclusive barrel ownership options.

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