Spontaneity: PROSPECTING FOR BUGS

If you’ve been bitten by the sour bug(s), why not take a chance on your own mix of microflora? With fairly simple tools and the right attitude, you could create a local blend that delivers something valuable. It’s a risk worth taking.

Within the gables of a crumbling gray row house facing a cobblestone lane in the shadow of Brussels’s Tour du Midi, a bit of magic is unfolding. As a venerable brewer shuts the front doors to his family-owned brasserie three floors below, a gentle breeze wafts through open windows and louvred vents. Swirling currents of air percolate through the brewery’s attic, dispersing a unique blend of microbes carried aloft from the banks of the Senne. The microorganisms settle upon a shallow open vat of tepid, turbid wort and begin the years-long process of transforming malt sugars into lambic, pride of the Pajottenland.

Such sepia-toned scenes are as romantic and alluring as the myth of the Wild West, but successful spontaneous fermentation leaves less to chance than legend suggests. Airborne bugs do make their way into Belgian wild ales, to be sure, but it is largely the resident microbes—caked on walls, joists, and barrels—that hold the signature terroir found in every bottle of lambic, gueuze, kriek, and framboise.

Indeed, the virtuosos at Brasserie Cantillon recently gained a bit of press for having sprayed down the brick walls and wooden rafters of their new building with a healthy dose of the brewery’s elusive lambic. The goal? Ensuring that the new location maintains the same blend of critters as the old one. It takes years—more than a century, in fact—to develop just the right mix for a classic example such as Cantillon Gueuze.

But, for New World craft brewers and homebrewers just staking their claims, the draw of spontaneous fermentation is just too powerful to ignore. With the right tools—and the right attitude—they’re out to create their own terroir.

Own the Risk

Let’s get something out of the way: You probably shouldn’t bother with spontaneous fermentation if you’re impatient or if you fear uncertainty. It’s unlikely (though not impossible) that you’ll capture a beautiful blend of microscopic creatures on your first try, so patience and persistence are key. You must let go of the need to be in total control, be willing to accept unknowable outcomes, and take things as they come.

Understand that embracing the indeterminate does not, however, mean shirking all responsibility. Even when you place your trust in the proclivities of anonymous microbes, you can still tilt the odds of success in your favor. Try to adopt a laissez-faire approach, yes, but don’t forget to measure, sanitize, and take good notes. You might never perfectly replicate the best wild ale you’ve ever made, but you don’t stand a chance if there’s no record of how you got there.

Equipment

Most of the equipment you use to brew standard ales and lagers can be repurposed and reused for spontaneously fermented beer, but it’s advisable to maintain a separate set of plastic pieces for wild fermentations. Stainless steel and glass are easy enough to sanitize that they can safely perform double duty (if your sanitation practices are good), but plastic is prone to scratching: Donate old buckets and bottling wands to the wild side and buy some brand-new equipment for your clean fermentations.

A couple of special pieces you might want to consider include the coolship and the horny tank. A coolship (from the Dutch koelschip) is nothing more than a large metal pan. The pan’s wide, shallow shape promotes rapid cooling of hot wort by exposing a relatively large surface area to the air. It won’t, however, cool off nearly as quickly as is possible with modern heat exchangers and wort chillers, thus leaving open the critical window of 80–120°F (27–50°C) within which most wild bugs thrive.

Coolships have largely gone the way of gas lighting and other nineteenth-century technologies, but they remain an important part of the traditional lambic brewery, and it’s easy enough to fashion one at home. All you need is a large shallow pan. Commercial roasting pans offer the ideal overall shape and are available from restaurant supply stores and online. Finding one of sufficient capacity can be a challenge, but if you have the cash (or know someone in the restaurant business), roasting pans as large as 42 quarts (10.5 gallons/40 liters) are available.

I’ve found that a full-sized stainless steel steam-table pan does the trick for less than $20 U.S. These measure roughly 20-by-12-by-6 inches (51-by-30-by-15 cm) and hold 5.25 gallons (20 liters). Reducing your batch size from 5 gallons to 4.5 ensures that there’s enough room for Kräusen, should you wish to conduct an open fermentation directly in the coolship.

In theory, spontaneous fermentation is as simple as brewing up some wort, trans-