When I ask Troy Casey what he calls himself, he's pretty humble: "A small-business owner." Which is true enough. Having only one other full-time employee, he does countless jobs both big and small for his Glenwood Springs, Colorado, company, Casey Brewing & Blending. That last word, though—blending—is the one vocational descriptor that separates Casey from most other brewers in America, and may very well be why he's currently producing some of the nation's most extraordinary beers.

"Brewers just make spent grain," he tells me, with no snark intended. He's referring to the by-product left over after the initial brewing process, in which malted grain is soaked in hot water until all the sugars have been extracted. Nevertheless, he doesn't correct locals and laypeople who casually identify him as the brewer, even if he's not one.

Yes, I'm telling you, perhaps the hottest brewer in America at the moment doesn't really brew. Instead, he buys other breweries' not-yet-fermented beer—known as "wort"—which he then totes back to his brewery, er, blendery....

"We look more like a winery than anything else," Casey explains, since his facility lacks standard brewing equipment, like mash tuns and brew kettles, and is instead dominated by barrels and blending vessels. Located next to the Roaring Fork River, 40 miles northwest of Aspen, Casey's headquarters are different from any beer-making facility you've probably visited in this country. Not least because the space was formerly a CrossFit gym. The kettlebells, chin-up bars, and tank top–clad bros were replaced in early 2014 with some 140 French oak barrels, four open-top puncheons, five brite tanks (where beer finishes conditioning), and, most importantly, Casey's blending tank. "What I'm doing with blending is trying to coax out certain flavors," he tells me. Flavors he would be unable to obtain from just a single batch of beer.

"Beer is made by men, wine by God," Martin Luther famously claimed—but even he'd have to admit that Casey's beers probably take the skills of both. Barrel-aging and spontaneous fermentation (that's the "God" part, I suppose, since it refers to fermentations in which commercial yeast isn't added) are notoriously unpredictable. Even with the exact same base wort, some barrels will turn out exceedingly sour, others mildly tart; some will be pleasant to drink, others might become so cheesy and funky that they necessitate dumping. You simply can't guarantee anything happening within a single barrel. That's why Casey chooses to blend together various barrels of different ages and flavor profiles to produce something that, dare I say, neither man nor big man in the sky could produce himself.

To be fair, what Casey is doing is not 100% sui generis by any means; just fairly unheard of in America, where only a few folks besides him are actually doing it. In Belgium, though, blending without brewing is a little more commonplace, especially at a top geuzestekerij. For years, the acclaimed Drie Fonteinen, just outside Brussels, was strictly a blendery, though they began brewing as well at the end of the 20th century. Nearby, Hanssens Artisanaal is the oldest blending-only brewery in the world, operating since 1896. And, in Wallonia, the predominantly French-speaking southern portion of the country, the relatively new Gueuzerie Tilquin buys wort from several different notable lambic producers; the purchased wort is aged in oak and then eventually blended together.

Casey has designed a few fairly simple base recipes for saisons and Belgian-style sours, which are brewed about once a week, mostly by the nearby Roaring Fork Beer Company. (To be fully honest, occasionally Casey will do his own hands-on brewing on location.) In an attempt to use nearly 100% local ingredients, Casey's wort is made with strictly Colorado water and grains, mainly wheat and barley, with only a small portion of the hops coming from afar. He sources aged hops from Europe; they've lost much of their bitter flavor and aroma, but still have the ability to prevent bacterial infection, which is perfect for the lambic-style offerings Casey so frequently toys with.

The wort—sweet and flat at the point when Casey receives it—goes into neutral oak barrels and puncheons for several months of patient aging and fermenting. Added to the barrels is a proprietary mixed culture of Saccharomyces, Brettanomyces, and Lactobacillus, which Casey has captured from the air. Beer geeks too often think these wild yeasts and bacteria guarantee amazing beer, but Casey admits they're not some "magic bullet." If they were, his blending skills wouldn't be an absolute necessity: "We pull samples from the barrels and do side-by-side comparisons to try and figure out what might work together."

Yes, of course, it's a little trial-and-error, but Casey—who has a BA in chemistry and a master's in food science, and who got his start in Coors' fermentation cellar—has made it a far more technical endeavor. He keeps a spreadsheet on his computer that monitors the changing characteristics of each and every barrel, noting which might have achieved the various flavors Casey is striving for, and are thus ready to blend.

"It's not simply a matter of blending the best of the best together, though," Casey explains to me. "You could take your two favorite barrels—together they taste terrible. But two average barrels blended together somehow become greater than the sum of their parts. You have to be able to recognize that."

Casey may be the American most celebrated for this skill at the moment, but other stateside blenderies have also begun springing up of late.

"Focusing on fermentation (and not actually brewing the wort) has many positive implications for an exclusively sour brewery like ours," says Jay Goodwin, a cofounder of The Rare Barrel. This Berkeley beer company gets all its wort from several Bay Area breweries, allowing it, Goodwin tells me, "to put more of [our] energy toward discovering how yeast and bacteria positively influence flavor."

Wisconsin's Funk Factory Geuzeria, meanwhile, has a stated goal of attempting to blend the most Belgian-like lambics this country has ever seen, sourcing its wort mainly from nearby O'so Brewing. Owner Levi Funk—yes, amazingly, that's his real name—sounds a lot like Casey when he describes his job.

"I don't have a lot of interest in the brewing side," he told Jason Stein of Paste last year. "I never really even home brewed. My interest lies in the fermentation, aging, and blending. The brewing side is technical, and I believe there are people much more skilled in the technicalities of brewing wort. The fermentation side is more of an art and where I like to play."

Okay, but are these "artists" like Funk just slackers, skipping out on hard and messy brewing work—or are they better able to create their great beers because they focus exclusively on what they think most matters in sour-beer production? I would tend to say the latter. Funk's beers, spontaneously fermented in an open-air coolship from the random yeasts and bacteria floating all around us, do a brilliant job of emulating iconic Belgian sours. Take Door Kriek, a blend of lambic-style beers aged in French oak wine barrels, then re-fermented with tart cherries. An obvious homage to Belgian kriek, it's earthy yet quite tart, like a homemade cherry pie. The Rare Barrel presents a more Americanized take on blended sours—these beers are less rustic, with fruits and spices added that you wouldn't likely see in Belgium. My current favorite is their Home, Sour Home, an oak-barreled golden ale aged with peaches, cinnamon, and vanilla beans. In my opinion, though, Casey is this country's blender par excellence.

His flagship saison, simply called Saison, is dry and funky, recalling the open-air farmhouse ales of Wallonia. There's also Oak Theory, Casey's take on a classic Senne Valley sour, like those coming from the legendary Brasserie-Brouwerij Cantillon. It's bright and citrusy with a white wine–like acidity, a valiant attempt at American gueuze. But it's Casey's more limited offerings that show how he really flexes his blending muscles—especially when he also begins playing with fruit.

One hundred percent Colorado-grown fruit is one of Casey's biggest blending weapons, and, in limited releases like the Fruit Stand Series, The Cut Series, and Casey Family Preserves, he truly gets to take beer to a place rarely seen in this country. The western slope of Colorado has an amazing variety of fruits: Balaton cherries, Laredo plums, nectarines, blackberries, and peaches—even cab franc grapes. Casey will often add up to 3.5 pounds' worth of these fruits to each gallon of beer. The fruit is always freshly picked, unwashed, and frequently thrown in the barrels whole. Many brewers purée their fruit additions, something Casey feels oxidizes the ingredient and strips it of flavor.

"It was important for me to differentiate myself, since most brewers get the same ingredients from where everyone else does," Casey tells me. "We're making old-world styles of beer," he says, referring to "when farmers would make beer using whatever they grew on their own farm. That was what I wanted to do, too. Luckily, Colorado is one of the few states where you can grow pretty much everything you need."

As with the actual brewing, Casey prefers to leave the orchard work up to the true professionals. When I ask him what these fruit farmers actually think about his atypical beers, he responds, "They seem very proud to have their product involved with us, but I'm not sure they really like the beer. They all are very polite, though—'Thank you for the taste.'"

Beer geeks, wine aficionados, and food lovers will be blown away, however, by Casey's releases. The barrel-aging and blending give these beers an extraordinary complexity, a pleasant fruitiness and acidity, and delicate carbonation. Casey's fruited beers show off the real essence of each ingredient he uses—never cloying or artificial-tasting. He's also getting more and more experimental with both ingredients and barrels. Recently, I was floored by something called Advanced Oak Theory, Casey's flagship offering, aged in former Stranahan's Colorado Whiskey barrels. The beer was exceedingly layered: opening with aromas of caramel and vanilla, then punching your palate with oaky spice, quickly transitioning to a tropical-fruit acidity, and finally finishing with that puckering tartness you'd actually expect in an American wild ale.

Sadly, though, I have to break your heart and tell you it's not going to be very easy for you to ever taste Casey's beers. He makes fewer than a thousand barrels per year (by comparison, Sierra Nevada makes 500,000 barrels a year of just its pale ale). The brewery's hard-to-reach river valley area is not exactly a beer geek haven, either, so most of Casey's beers appear on tap at the kinds of small-town, local joints where you wouldn't typically expect to see sour beer served—family pizzerias, for instance. Visitors to nearby Aspen also make up a large part of Casey's clientele, and a few of his more mainstream offerings occasionally escape to the more populous Front Range area of Colorado, a couple of hours' drive away.

On the first weekend of each month, Casey opens his brewery doors to the public to sell small pours for drinking there and bottles to go, his parents and wife often helping out with the necessary odd jobs. That suits Casey just fine. If he had it his way, he would probably prefer to focus his attention on doing just one thing:

"It would be arrogant to assume I could grow fruit better than a farmer. Or barley and hops better than growers. That I could malt better than a maltster. It's a romantic notion, sure, to think one person could do everything.

"But my true specialty is in fermentation. And blending."

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