Wild ales are scarce and beautiful creatures, rarely imagined let alone seen. Few dare to brew them. Most brewers fear them. Even in Belgium, where spontaneous fermentation defines the great lambic beers of the Senne Valley, the process is only attempted seasonally when the right combination of microbes float in the vicinity. Under most circumstances, spontaneous fermentation is a destroyer of beer—something to avoid, not attempt.

Let’s be clear on what a wild ale is—and isn’t—as the nomenclature is often misapplied. Wild ales are beers into which no cultivated yeast strains are used. This contrasts dramatically with modern brewing, which has spent centuries learning to isolate and purify yeast strains and sanitize against contaminants. In wild ales, the wort (unfermented beer) is simply exposed to the open air and allowed to ferment spontaneously, courtesy of any ambient yeast or bacteria that wanders by.

Beers brewed with laboratory-cultivated Belgian-derived yeast or bacteria such as Brettanomyces or Lactobacillus share similar characteristics, but aren’t properly “wild.” Neither are beers aged in barrels inoculated with these or similar strains. Call them sour ales, Brett beers, or lambic-style—they’re causing enough stir to merit new categories in brewing competitions. But like animals in the controlled environs of a zoo, they’re not truly wild.

The trouble with attempting a wild ale is that the brewer is at the complete mercy of nature. Select your grains and choose whatever hops you care to, but with a wild ale, nature picks the yeast. And she’s known to be a bit fickle. There are thousands of yeast and bacteria species out there, the vast majority of which have no business in a beer. Opening up unfermented wort to the randomness of nature’s yeast portfolio is like spinning a roulette wheel in which the odds are disastrously against you. You’re either a fool for trying—or maybe you’re Phil Goularte.