Brian Horton's secret ingredient for fantastically unique beer floats in the air, sight unseen in a cavernous shed behind his Divide-based brewery.
Not even he knows exactly what it is.
But Horton wields this mystical ingredient nonetheless - a seemingly magical feat made possible with a brewing technique called spontaneous fermentation, which he and a small band of adventurous brewers in Colorado fervently embrace.
It isn't wizardry, but rather a high-stakes game of chance that hearkens to the very roots of this craft.
"We get the flavors out of it we like to taste in a beer," said Horton, a founder and brewer of Paradox Beer Co. "That experimentation drives us."
Spontaneous fermentation dates back to the first batches of beer ever made.
It was the only way to make beer before refrigeration and super-pedigreed species of yeast lent precision to the art. And as technology advanced and beer became a multibillion-dollar industry, spontaneous fermentation became a cumbersome, risky and outdated means to supply the nation's suds.
Even now, few craft breweries dedicate their resources to it. That's because Mother Nature adds the final ingredient: yeast and other airborne microbes.
"This is the most ancient way of creating beer there is," said Andrew Sparhawk, of the Brewer's Association and craftbeer.com.
The standard bearer in spontaneously fermented beers are Belgium-based breweries churning out lambic and gueuze brews - styles unique to that region.
But a few stateside brewers - Allagash Brewing Co. in Maine and Jester King Brewery in Texas, for example - are producing their own variations. Black Project in Denver only makes beers using this bygone process, making it a leader in this niche market. (Full disclosure: I learned about this style while sipping beers at another purveyor of this style, Wiley Roots Brewing Co. in Greeley, where a friend of mine pours beers a few nights a week.)
In the Pikes Peak region, Paradox is joined by Trinity Brewing Co. as practitioners of these dark arts.
Their work typically begins in a coolship - that flat, pan-like steel vat where these brewers pour their boiling-hot wort (the sweet, unfermented liquid mixture of grains, hops and malts that results from the mashing process).
There, the wort cools while naturally collecting yeast and other microbes from the surrounding air.
To pitch any additional yeast is anathema to purists of this sacred art. And brewers disagree on how long the wort can be left in the open for it to truly be dubbed "spontaneously fermented."
Even adding fruits - their skins laden with natural yeasts - makes it something else entirely: a spontaneously inoculated brew.
It all carries risk.
Bad bacteria can easily settle into the wort and spoil it, especially if it fails to cool quickly. Different yeasts imbue different flavors, leaving the beer's ultimate outcome a mystery.
And while most beers take only a couple of weeks to make, these are left to age for months - sometimes years - in whiskey, wine or bourbon barrels. Often, brewers will mix different batches of spontaneously fermented beers to refine those flavors or add another layer of complexity.
"We talk about brewing being an art and a science," Sparhawk said. "On the science side of it, nature is taking its part in the brewing process. It's a financial risk, because you don't know what's going to come out of those barrels."
Fall and spring are usually the best seasons to practice this brewing style, because the temperatures are low enough for the wort to properly chill, and the best microbes are floating in the air. But some brewers are always willing to experiment.
Paradox recently upped its game with a coolship housed in a new shed whose interior walls are lined with the staves of deconstructed wine and whiskey barrels.
Not only is the design aesthetically pleasing, but it also will allow an extra layer of flavoring to develop in these beers, when condensation from the boiling wort gathers on those wood panels and drips back into the wort.
On a recent summer day, Horton and his crew broke in the new facility by riffing on this brewing process using a simple farmhouse-style mash made of pilsen malts and raw red wheat.
Because the weather was so warm, they first ran their wort through a machine that quickly dropped its temperature from boiling to about 85 degrees.
Then they dumped in about 30 pounds of peaches, plums and nectarines - inoculating it with all the yeasts they carried - and let it sit exposed in the shed for a few days to pick up more microbes.
In the fall and spring, they'll hew more closely to the actual spontaneous fermentation style. In other words, they'll do without the fruit and let Mother Nature go it alone.
Will every batch ferment without a hitch?
Of course not, Horton says.
"But when it does, it's magical," he added. "We're always chasing that magic."