Anyone who's ever tasted unaged white whiskey alongside an aged bourbon can immediately tell the difference. The young one is abrasive, a little harsh and higher in alcohol. The one that has been around for a few years is mellower and more complex. The difference is time spent in a barrel, in contact with air and charred wood.

Barrel-aged cocktails A negroni (left) and a Manhattan at BLT Steak. The restaurant ages cocktails in charred wooden bourbon barrels behind the bar for weeks at a time. (Fritz Hahn/The Post)

Whiskey isn't the only spirit that benefits from aging – rum, tequila, brandy and even beer can get better with time. What you might not have known: Cocktails can, too. For proof, check out the new barrel-aged cocktails at BLT Steak. Bartenders Rico Wisner (formerly of Topaz Bar and Bar Rouge) and Steve Oshana (formerly of Elisir) have begun mixing negronis and Manhattans and then laying them down in charred oak barrels behind the bar for several weeks.

The first thing you'll notice: Barrel-aged cocktails are very easy to sip. Negroni fans will notice that aging lessens alcohol's edge, mellowing the Aperol's bitterness and the gin's juniper snap. Instead, all the flavors are incredibly balanced and blended almost seamlessly. Poorly mixed drinks can lead to a stratification of ingredients: For example, you might taste the gin first, and then the vermouth, and the Aperol in the finish. With barrel aged cocktails, the focus is on the whole.

Another benefit: "It doesn't have that bite that some people don't like," Wisner says. "It's more approachable."

The Manhattans and negronis are available now, and Wisner explains that the goal is to have up to five different drinks available at once. Next up: a blend of Milago tequila, chai tea liqueur and Licor 43, which is in a barrel now and should be ready at the end of this week. "I really like silver tequila with tea and vanilla," Wisner says. "I just enjoy the flavors."

Barrel-aged cocktails sell for $14 each, in line with the steakhouse's other $14-$15 mixed drinks. To get the most value, sample them during the bar's weeknight 5@5 happy hour: selected appetizers, including blue cheese-and-BBQ sliders, beef tenderloin skewers and broiled oysters, are $5 from 5 to 6:30 p.m.