From northern Minnesota, a father

Russ Karasch opened a plastic bag filled with strips of wood the color of the best part of a piece of toast.

"Smell this," he said.

The aroma was intoxicatingly comforting, like roasting a chocolatey Scotcheroo bar over a campfire made of cinnamon sticks, if such a thing were possible. It's amburana wood, a Brazilian variety, Karasch said. And in a way, it represents the vast possibilities this expert barrel-maker is creating for the future of wood-aging spirits.

As craft distilling grows nationwide — in many ways mirroring the rise of craft brewing a decade ago — demand is creeping back up for the time-honored art of cooperage, or barrel-making. And some of the biggest innovations in barrels are happening in Minnesota; specifically in Park Rapids, Minn., off a side street between the airport and the police station.

Karasch and his daughter, Heidi Korb, launched Black Swan Cooperage in 2009. Since then, the duo has become recognized across the distilling, brewing and winemaking industries for creating barrels and barrel-adjacent products that simply make beverages taste better, faster.

"Heidi's barrels will do in six weeks what a traditional barrel will do in two years and seven months," Karasch said. "That's huge in the industry."

To understand how they’ve managed this, let's go back to elementary school science class.

Do you remember putting a stick of celery in blue-dyed water and watching its color change? When Karasch did this experiment as a grade-schooler, the eureka moment came when he sliced the celery in half and saw that the dye was actually traveling up the stalk through what looked to him like little straws — xylem and phloem tubes, the plant's water and nutrient transport system.

Continuing the comparison, he said, we can understand how barrels work by imagining a plank of wood as a rectangular bundle of drinking straws. In a standard barrel, the spirit comes into contact with the wood's side-grain, which is like trying to force water through the side of a straw. But what if he could expose the end-grain, so the liquid could be absorbed into the wood like sipping a milkshake?

After working with several university researchers, he found that the data supported his theory. The average rate of penetration of liquid into the side-grain of quarter-sawn white oak, he determined, is 1.67 thousandths of an inch every seven days. On the other hand, into the end-grain, the rate jumps to 15.89 thousandths of an inch every seven days — about nine times faster.

The next challenge: How do you expose the end-grain without compromising the barrel's effectiveness?

Karasch went into testing mode. After quite a bit of trial and error — and several snapped barrels — he developed the three types of barrels Korb's team makes today.

One is a traditional barrel, and the other two have patented patterns carved into each stave. The Black Swan Standard barrel features staves with cross-cuts, or horizontal incisions across the wood, and the Honey Comb barrel includes a combination of cross-cut staves and ones with shallow, cylindrical holes drilled in a precise honeycomb pattern. This design is in fact so effective at infusing flavor into liquid that a spirit aged in an all-honeycomb barrel, Korb said, would be like "drinking liquid white oak."

Just about every part of Korb's cooperage process is aimed at coaxing the best possible flavors from the wood.

To bend the staves into the classic barrel shape, Black Swan uses a hot-water bath. Many cooperages use fire to relax the wood, but Black Swan uses the more labor-intensive water method because it helps leach out excess tannins.

Plus, all their barrels are toasted.

"This is where we like to say the magic happens," Korb said as we walked into the toasting room. On one side of the room, four barrels each sat over small bonfires. There isn't a predetermined amount of time a barrel toasts: It has to smell right.

What's happening here, essentially, is the natural sugars in the wood are being caramelized, Korb said, which allows flavorful compounds like vanillin to be more easily extracted by the spirit that’ll age in the barrel. Any barrel-aging process introduces flavor to the liquid inside, but a spirit aged in a toasted barrel tends to have stronger notes of toffee, vanilla and baking spice in particular.

Then, the interior of the barrels have to be fully charred, a legal requirement. The worker in charge of the toasting and charring room placed the barrel over another small bonfire inside a floor-to-ceiling fume hood, picked up a hose of compressed air, and went to town, Fahrenheit 451-style. For a few brief and bright seconds, a 10-foot-tall vortex of fire shot out of the top of the barrel, swirling like a cartoon tornado. Then, he doused the barrel with water to stop the fire. Peek inside, he said: The entire interior of the barrel is a pure pitch-black.

But wait — they’ve just spent hours cultivating a specific and nuanced level of toasting, and now they’re incinerating the inside of the barrel to charcoal?

Yes and no, Korb said. True, charring the wood essentially nullifies any toasting, but the low-and-slow toasting process penetrates deep into the wood while the flash-fire creates just a thin layer of char. So the spirit filters through the top layer like a charcoal-based Brita water pitcher, she said, and then develops its deep flavor as it absorbs into the much thicker toasted layer behind the char.

After a glorious trip through the toasting room, it's back to the workshop for the final steps. The temporary metal rings are replaced with the galvanized steel hoops that’ll permanently hold the staves in place, and a barrel head is snapped into each side. Finally, the barrel is water-tested, a spigot-like bunghole is drilled, and the head is stamped with Black Swan's logo.

Finally, the barrel is ready for prime time.

At Black Frost Distilling in New Ulm, distiller Jace Marti uses the company's cross-cut barrels, which he said are especially effective given the way colder climates slow extraction. The distillery only opened last summer, so their barreled spirits — made with all Minnesota-grown grain, too — aren't on the market yet.

A few months ago, Marti and his team blind-tasted their rye whiskey-in-progress versus a commercial four-year bottled-in-bond spirit.

"Our rye at six months has more sweetness than that one does at four years, and that is definitely a product of those cross-cut staves," he said. "It's still young; there are still things that need to mature out. But given that that sweetness is already there, it changes the way that spirit is going to mature."

Even their white whisky, which is unaged, has a subtle and spicy sweetness. At Black Frost's cocktail room, it's served in a truly delightful old fashioned — smoked with ambruana wood chips from Karasch.

Meanwhile, back in Park Rapids, Karasch is going back to the drawing board.

Sitting in his office, surrounded by small barrels, variously sized chunks of wood, and plenty of achievement awards and sawdust, Russ Karasch leaned back.

"Used to be, years ago, America: baseball, apple pie, Chevrolet, wooden barrels," he said. "No matter where you looked, a wooden barrel was always in the picture. Because everything was shipped in a wooden barrel."

No longer. Even as early as the 1920s, the barrel industry was defending itself against newfangled corrugated cardboard boxes and forklifts. After World War II, the invention of the overseas shipping container sealed the barrel's fate.

Back then — and, as Black Swan proves, still today — if you cared about barrels, you paid attention to Minnesota. Most issues of the late 1800s/early 1900s trade magazine National Coopers’ Journal contained a "Minneapolis Report" of the latest happenings in flour milling, apple harvests, and other industries whose success was tied to barrels.

Some things, clearly, have changed. In 1926, the Twin City Milk Producers Association used 7,000 wood barrels for powdered milk alone; today, barreled milk sounds more like a "30 Rock" cutaway gag than an actual consumer product. In 1913, the National Coopers’ Association held a general meeting in St. Paul; rooms at the then-new Saint Paul Hotel started at $2 a night.

But some things have not.

"There hasn't been a change in the way barrels have been made for 3,000 years, literally," Karasch said.

Facing an oak shortage of historic proportions — and armed with his data on how quickly liquid penetrates wood grain — Karasch isn't convinced that a standard barrel is the only good way to use our limited wood supply for spirits.

A solid, mature American oak tree — anywhere from 80 to 200 years old — produces about three good barrels. And after three years in a barrel, he said, liquid has only saturated about a quarter of the wood depth — meaning 75 percent of the wood in a barrel is just structural.

This is problematic, Karasch said, given that the oak supply is about to plunge. Currently, due to poor forestry management practices in the 20th century, the American oak population essentially lacks a good middle-aged generation. About 8 out of every 10 oak trees are mature right now, and far fewer saplings have taken root; this means that once today's mature trees are harvested, usable oak will drop precipitously for at least decades, perhaps a century or more.

And Black Swan is already feeling the effects. As of this winter, Korb said Black Swan was quoting potential customers a lead time of "north of eight months." It's not about labor, it's not about money — it's about materials. There is simply not enough white oak.

Rather than mill a centuries-old tree only to underutilize a significant majority of it, Karasch asked himself, why not replace the structural wood with another less endangered material and just keep the portion of the wood that adds flavor?

Enter the Squarrel. It's a square-shaped stainless steel barrel, taller than it is wide, with slats cut out of the sides so oak planks can be dropped in.

Karasch's invention uses about one-third the wood of a typical barrel — and shorter staves, too, so they can be made with surplus barrel wood to reduce waste even further. And not only is the metal structure reusable, but the Squarrel also stacks like a box and can be pressurized and tapped like a keg.

But another of Karasch's recent inventions asks an even bigger question: What if wood-aging spirits or other beverages does not necessarily have to involve barrels — or even oak — at all?

Nearly every barrel worldwide is made from oak, and the reason is mainly practical. Barrels are held together with sheer force, no adhesives, and the wood has to be strong enough to withstand the pressure. Certain woods that are more aromatic make bad barrels. Maple is leaky. Cherry is too porous; a spirit in a cherry wood barrel would evaporate through the wood rather than aging inside. Oak has both a tight grain and naturally occurring sugars, so it's the right balance of effective and tasty.

Black Swan's Honey Comb wood sticks get around this challenge by simply not being a barrel. The sticks are long and square-shaped and, similar to the honeycomb staves, are drilled through with holes in a carefully measured pattern. A distiller, beer brewer, winemaker, or even cocktail bartender can drop one or several into a stainless steel vat or other container to let the wood flavor infuse, like a tea bag.

With accurate timing, the spirit can penetrate and extract flavor from 100 percent of the wood — a structural impossibility with traditional barrels. And watertightness is no longer a factor, so Karasch can explore wood-aged flavors that distillers previously could not access.

To return to cherry wood, for example: In this case, the wood's porosity actually helps it more easily impart its unique flavor profile of dark fruit and buttery toast. Hickory will infuse a honeyed or candied bacon quality, whereas white ash — what Jace Marti is using on the current cocktail room menu at Black Frost Distilling in New Ulm — gives bready, marshmallow flavors.

When Marti test-aged overproof rum on amburana wood Honey Combs, he found it only needed contact with the wood for about a week before it was perfectly aromatic. He's hoping to release the product this year.

So far, Karasch has tested 54 species of wood for Honey Combs. Currently, nine are available for sale.

"So if I’m going to get the rest done before I die, I’m either going to have to speed up the process or live a lot longer," he said.

There are still wrinkles with the Honey Comb, Karasch conceded: Part of the appeal of wooden barrels and even Squarrels is that they allow very small amounts of air to come into contact with the spirit in a process called micro-oxygenation, which a Honey Comb in a steel vat simply cannot replicate.

Don't worry; Karasch is still tinkering. He's got a new idea to solve this, but he can't tell me about it just yet.

None of this is magic, he reiterated. It's science — and a lifetime of fascination with wood products and decades’ worth of barrel-making, of course.

"I’ve been accused of being pretty damn good at what I do," Karasch said. "I get these scientists that come to me and ask me what I know, and they combine it with their knowledge. We’ve just figured out how to take advantage of the wood properties."

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