Distiller Eddie Russell pours another taste of bourbon into the dozen outstretched glasses before him. “Whatever you don’t want, just dump it on the floor,” he says, motioning to the wooden planks below. Everyone laughs; none of the whiskey geeks he’s hosting today would dare spill a drop onto the Kentucky ground. Because they’re drinking straight from Wild Turkey’s most prized barrel stash, the ones that will be sold off to individual buyers for $10,000 each and the ones that even the most savvy among them will probably never get to taste again.

Wild Turkey, along with many other bourbon and whiskey producers across the country such as High West and Jim Beam, now let customers visit its distillery and pick out their own barrels to take home. These single barrels—which are also referred to as private barrels or barrel selects—are only sold to liquor-license-carrying professionals, but they’re in such high demand among the booze nerds of the world that bars and liquor stores can barely keep up. Even big-box stores like Sam’s Club are now offering single barrels to their shoppers.

Untitled Supper Club, a speakeasy in Chicago, has more than 150 single-barrel whiskeys—including barrels from Wild Turkey—and even employs its own whiskey librarian. Beverage director Egor Polonskiy says he has trouble keeping some single barrels, such as Buffalo Trace Blanton’s, in stock. “You can taste the true heart and soul of a distillery in single-barrel products,” he says. “And people who have been drinking whiskey for a while are looking for that higher proof, more intense, really flavorful stuff.”

Whiskey you buy off the shelf is a combination of hundreds of different whiskeys, each having aged in different barrels at different lengths of time, and blended to create a uniform whiskey. But a single barrel is not blended. It will of course vary in flavor and A.B.V. from the product you find on the shelf, but it will also differ even from the barrel sitting next to it in the rickhouse, or aging warehouse, shelf. No two barrels ever taste the same. “That’s always a pleasant surprise for whiskey lovers,” Polonskiy says. “Once the barrel is gone, it’s gone forever.”

For spirit collectors and connoisseurs who are always looking for the most special bottles, it doesn’t get any rarer than single barrels; most distillers only release 100 per year. In general the price of a barrel is equal to the price of how much spirit is inside of it. A single barrel contains about 53 gallons of liquid, which works out to 27 cases of bottles. The distiller then sells the bottles to the customer at wholesale price, which can vary by market. For Wild Turkey, a barrel will run you $8,000 to $10,000; the company doesn’t upcharge from its wholesale price.

Russell, Wild Turkey’s master distiller, uses a mason hammer to knock the cork out of another ancient barrel in his rickhouse. He dips in his copper whiskey thief, as the siphoning tool is known, and offers out another taste. This is what a typical tasting tour is like for those interested in buying a single barrel: You show up to the Wild Turkey property in Lawrenceburg, Kentucky, and Russell uncorks up to 10 barrels for you to sample before choosing your favorite. But Russell says customers usually just go with the first one they try. “After four or five you’re going to forget about what those last six tasted like,” he says.

Labeling single-barrel bottles at the Wild Turkey distillery.

Labeling single-barrel bottles at the Wild Turkey distillery.

Choose the barrel you like best and the distiller bottles it and personalizes it for you, affixing a special label or tag to the bottle that includes the buyer’s name, details about the batch’s aging process and a bottle number. “For marketing and advertising alone, it’s worth it,” Russell says. If someone wants to taste that specific barrel, they have to travel to your bar or liquor store. “You have the opportunity to try a barrel, pick one and go back and tell people about it. You’re hand-selling them to your customers.”

If you can’t make it to the distillery’s property for a tasting, the distillery can also send you samples in the mail. “It can be a complicated process, but it’s fun,” Polonskiy says. “If you get samples shipped to your bar, you can gather all the bartenders together and choose the favorite. It becomes all about the relationship with the suppliers and distilleries.”

Two months after you pick your single barrel, you’ll receive the barrel—yes, the physical barrel your spirit was stored in—and your cases of alcohol. Most bars and stores display the empty barrel, which is a great conversation piece for customers, or even use it to make beer in.

So what do they do with the single-barrel product? Some bars come up with signature cocktails for their uncommon goods, but at Untitled, customers rarely ask Polonskiy to make cocktails with the product. “There’s no right or wrong way to drink your whiskey, but single-barrel is an exception to me,” he says. “It’s a showcase of the producers’ quality and style. You should drink it neat to understand it.”

Gimmicky, maybe, but it’s also big business. In fact, these single-barrel programs are no longer exclusive to whiskey. “We actually go even further than bourbon and rye now,” Polonskiy says. “We had a private barrel of Maestro Dobel tequila delivered recently.”

Tequila is poised to be the next big thing in single barrels. Patrón Spirits began its own buy-a-barrel program last fall and invites customers to visit its luxurious Hacienda Patrón in Jalisco, Mexico, to taste and select their own bespoke barrels. For Patrón, the price of a barrel varies based on what type of tequila is in it: añejo tequilas will cost a bit more than reposados because they spend more time aging in the barrel.

“Our master distiller and his team blend different barrel types, different wood, different lengths of aging to create [Patrón],” Patrón Spirits spokesperson Greg Cohen says. “We thought it would be really interesting if we gave people an opportunity to sample those different tequilas that are aging in those different barrel types over the different lengths of time, on their own. Each is very unique.”

Like whiskey, when these different barrels of tequila are blended together, they become what people know as Patrón. “But when you taste those barrels individually, and there are so many different combinations, you get really distinct and different tastes,” Cohen says.

One of the first bars to receive a Patrón single barrel was the Refinery Rooftop (http://www.refineryrooftopnyc.com/) at the Refinery Hotel in New York. Bar manager Chris Byrne uses the reposado tequila like he uses regular Patrón: in margaritas and for shots. “People think it’s unbelievable,” he says. “They say they’ve seen barrels of bourbon before, but never tequila. They love the backstory and keep coming back to drink it again.”

But buying a barrel isn’t for everyone. For the most part, you have to purchase every bottle that comes out of the barrel. That’s a lot of bottles. Not all bars have the money or storage space to buy that many cases of alcohol at once. “This is about a store or a restaurant offering their customers something they can only find there,” Cohen says. “And when they are gone, they’re gone. That’s very exciting for consumers who are looking for something different that they can’t find anywhere else.”

Byrne says even people who aren’t typically tequila drinkers will want to try it because they’re so intrigued by the story. That allure is part of the single barrel business strategy: Even if a customer can’t tell the difference between the taste of the single-barrel product and the traditional product, they tend to order the single barrel because they’re convinced it’s unique. At Refinery Rooftop, they ran through their cases of single-barrel Patrón in two months. “We’re actually expecting another barrel to be delivered in about two weeks,” Byrne says.

The demand is only expected to increase, Wild Turkey distiller Russell says, as he uncorks yet another bourbon barrel to siphon out samples. “Everybody wants something no one else’s got.”

Alyson Sheppard is the resident hangover specialist at Playboy.com. She taste-tested single barrels of Wild Turkey on a recent trip to Louisville. Follow her on Twitter: @amshep