Here’s What Happens When You Age Whisky

Hint: The barrel really does matter

scotch barrels
Scottish Viewpoint Picture Library/Scottish Viewpoint/Corbis

Technically, it only takes a few days to distil a barrel of whisky, but it takes time for that golden beverage's taste to mature. Although you could drink it straight away, it wouldn’t be the peaty, rich liquor that whiskey fans typically relish. So what transpires in the months, years or even decades that a whiskey is left to age?

When whisky is first distilled and sealed up in its barrel, it’s more like moonshine than what you’d expect from a spirit like scotch or bourbon. Instead of golden-brown, brand-new whisky is perfectly clear and tastes a lot like the malted barley it’s made from. But as soon as it goes into a wooden barrel, things start getting interesting, Camper English writes for Popular Science.

For every batch of whisky, there are two major factors that determine what it will taste like decades into the future: the wooden barrel it’s aged in and the environment the barrel is stored in. Traditionally, whisky is aged in oak barrels that are either toasted or charred when they are built, creating a layer of charcoal that filters out the raw spirit’s unwanted flavors, English writes. Through a chemical process called adsorption, the molecules that make young whisky so harsh are drawn to the barrel’s wall, creating a thin layer of everything you don’t want in a drink. At the same time, the wood adds flavor to the whisky, slowly infusing the liquor with lignin and vanillin (for vanilla-like taste), lactones (for a buttery flavor) and tannins or “wood spice” (which makes the whisky dry).

Traditionally, new barrels are used to age bourbon; once they are finished, the bourbon-soaked barrels often go to scotch whisky distillers, who let their product sit for longer to tease out the remaining flavors. And once you start getting into scotch, there’s a whole new chemical component to be reckoned with -  phenols, introduced when burning peat is used to dry the barley - which gives that type of whiskey its distinctive smoky flavor. 

“The longer you age, the more the phenols bond with other things in the solution to form new compounds like phenylated carboxylic esters, which tend to taste like honey,” Lost Spirits Distillery’s Bryan Davis tells English. “In a way, you trade smoke for honey.”

Climate also plays a big role in the whisky’s taste. Bourbon distillers often age their whisky in dry environments that help it evaporate and concentrate faster than scotch, which is usually aged in humid climates, Kara Newman reported for Slate. Most times, the older the whisky, the more complex the taste and the pricier it is. The oldest whiskies available are aged for 50 years and can sell for up to $25,000 a bottle, in the case of Glenlivet’s 50-year-old single malt scotch. But while rare half-century old whiskies might draw looks of longing from connoisseurs, there’s often a point at which the liquor’s age starts to show.

“It is possible for a spirit to get too old,” Dave Pickerell, a former master distiller for Maker’s Mark, tells Newman. “Sometimes older is better—but sometimes it’s just older.”

Old whiskies might cost a pretty penny, but for the flavor, Pickerell recommends choosing a more middle-aged whisky – 6 to 10 years for bourbon, and about 20 years for scotch. Any older, and you might just be paying for age, not flavorful beauty.

Get the latest stories in your inbox every weekday.