The Black Swan Barrel company in Park Rapids is not a quiet place.

Industrial wood planers shape white oak into staves. Workers bind them with steel rings, submerge them in hot water, then sear the inside with fire.

According to business owner Heidi Karasch, it's especially loud right now. Her workers are rushing just to meet the rapidly growing demand for whiskey barrels.

"We're over 10 months behind right now," she said. "So if you wanted to place an order today, you'd have to wait."

Dan Lehmkuhler toasts the inside of each barrel, building a small fire inside it, then stoking the blaze with compressed air at Black Swan Barrels in Park Rapids. John Enger | MPR News

As many as 40 barrels leave the shop every day, and Karasch's 15 employees, known as coopers in the industry, are always trying to improve that number. But it wasn't always so busy. When Karasch first started the business in 2009, it was something of a gamble.

Barrel making as an industry has had some hard times. Black Swan is one of only a few dozen producers left in the whole country. There used to be dozens just in Minneapolis. They were as common as mechanics, or concrete layers. These days, the whole state has just two.

But as a student at Ridgewater College in Willmar, Minn., back in 2007, Karasch noticed a steep rise in hipsters growing large beards and buying craft beer. Small artisan breweries were popping up all over the place.

She figured, the craft distilling industry wouldn't be far behind, and they'd need barrels.

Heidi Karasch and her father, Russ Karasch, run Black Swan Barrels in Park Rapids, Minn. John Enger | MPR News

"The craft distilling industry was still very young at that point," she said. "But we knew there was something coming and something good."

Her father, Russ Karasch used to make barrels for a cooperage in the metro area before it went out of business. He knew the trade and had some machinery. So when Karasch graduated, she went back home, rented a small building and got to work.

She was right about the craft distilleries. There were just a handful in the state when she started Black Swan. Now there are at least 14. Across the country, Russ said the industry is growing even faster.

He said the number of small distilleries has quadrupled in the last year. The drinking populations of China and India are also developing a taste for American whiskey. Major producers like Jack Daniels and Maker's Mark are shipping thousands of barrels overseas.

Barrels are soaked in hot water to make the oak more flexible before hydraulic presses force them into shape at Black Swan Barrels in Park Rapids. John Enger | MPR News

Demand is rising, but he said there aren't many new barrel makers starting up. That's because a whiskey barrel is really hard to get right.

"I know of a few cabinet makers that tried to move into barrels," he said. "They couldn't make it."

A barrel has to hold liquid for many years without using any glue, or gaskets. And it has to taste good.

At the center of the workshop is the toasting room. It's dark and smoky and incredibly warm. Karasch said, that's where the most important work is done by one of her best coopers — Dan Lehmkuhler.

Lehmkuhler explained the process while stoking a dozen small fires inside as many new barrels. He said it's the toasting of the barrel that gives a whiskey its flavor. It's his job to keep them over the flame just long enough to bring out the oak's natural sweetness.

"I like a sort of brown sugar smell," he said. "You know, almost like a cake that just came out of the oven. That's what I'm looking for."

Two whiskey barrels are finished and ready to ship from Black Swan Barrels in Park Rapids. Black Swan builds as many as 40 barrels a day. John Enger | MPR News

A few seconds can mean the difference between bitter and smooth whiskey.

It's a hard job, but between the exports and craft movement, Karasch said it's a good time to be a cooper.

Correction (Aug. 23, 2016): A photo caption in an earlier version of this story misidentified the hydraulic press process.