Bugs Gone Wild!

In the right hands, normally unwelcome microflora deliver ales that challenge the senses and stir the soul—quite the accomplishment for creatures we can’t even see.

Dave Carpenter Apr 12, 2017 - 9 min read

Bugs Gone Wild! Primary Image

Biology was never my favorite science class. But through personal growth and regular examination of inspiring beverages, I have come to appreciate the life sciences. Whiskey, wine, and sake wouldn’t be possible were it not for barley, grapes, and rice, respectively. And we have the agricultural duet of malt and hops to thank for ale and lager. But, of course, it’s at the microscopic level that the real magic happens.

A well-worn axiom says that brewers make wort and yeast makes beer, but an increasingly relevant corollary also recognizes the roles of rogue yeasts and spoiling bacteria. Most modern brewers go to great lengths to keep contaminating microbes out of the brewery, but for those who create wild and sour ales, renegade bugs are the keys to complexity.


Yeasts are single-celled members of the fungus family. They are eukaryotic, meaning that their cells contain a nucleus, mitochondria, and other premium options. A broad class of organisms, yeasts span the full range from beneficial to pathogenic.


When brewers talk about yeast, most of the time they mean one genus in particular: Saccharomyces. Saccharomyces cerevisiae and Saccharomyces pastorianus are ale and lager yeasts, respectively. Generations of brewers have selectively pressured these microbes for desirable and repeatable brewhouse performance characteristics. From fermentation to flocculation, every strain of Saccharomyces tells a unique story of the countless brewers who have subtly nudged it along its path from the skins of ripe grapes to a foil sachet that comes in the mail. Even in wild and sour beers, Saccharomyces remains responsible for the bulk of fermentation.


Saccharomyces delivers flavors and aromas that we generally find favorable because we’ve bred them that way. From the spice and fruit of Belgian Trappist strains to the barely noticeable sulfur of Bavarian lager varieties, Saccharomyces is well behaved and predictable. It’s domesticated. And it’s for this reason that any beer not fully built around Saccharomyces is called “wild.”

Brettanomyces (a.k.a. Dekkera)

If Saccharomyces strains are house cats and pet dogs, then Brettanomyces strains are cougars and wolves: related but distinct. Named for the English barrels from which these bugs were isolated (the name means “British fungus”), Brettanomyces is the name for a genus of yeasts that catches us off guard.

While Saccharomyces is associated with agreeable descriptors such as “fruit,” “spice,” and “clean,” the terms bestowed upon Brett are less complimentary: Sweaty, funky, barnyard, horse blanket, adhesive bandage, gym socks, and overripe cheese are among the more polite terms. In extreme cases, Brett is even described as having the je ne sais quoi we normally attribute to latrines.

But when Brettanomyces is used with care, it delivers beautiful qualities that can’t be achieved any other way. Breaking down complex sugars that Saccharomyces can’t touch (and, in some cases, even wood itself), Brett strains create everything from the rustic, earthy flavors of B. bruxellensis to the overripe pineapples and mangoes of B. anomalus.


Despite its surging popularity, Brettanomyces still isn’t understood nearly as well as its domesticated brethren. Indeed, a recent development in the story of Brett is the discovery that the Drie Fonteinen strain (B. bruxellensis var. Drie) isn’t even Brett at all, but rather a rowdy strain of Saccharomyces cerevisiae. We clearly still have much to learn.

The yeasts Saccharomyces and Brettanomyces are only the beginning. To achieve the acidic, sour notes we associate with lambics and Flanders ales, we must turn to bacteria.


Like yeasts, bacteria are single-celled organisms. But bacteria are prokaryotic, meaning they have neither nuclei nor membrane-wrapped organelles. If we liken Saccharomyces and Brettanomyces to the domesticated and wild relatives of common felines and canines, then the many varieties of bacteria are more akin to alligators and crocodiles: primitive, untamed, and unpredictable.

Lactobacillus and Pediococcus

Lactobacillus is what gives yogurt its tang, and aficionados of sour ales readily recognize the tart acidity of lactic acid in a wide range of styles. From Berliner Weisse and gose to lambic and the reds and browns of Flanders, lactic acid is that pleasant tartness that initially surprises but eventually seduces.


Lactobacillus has the potential to deliver lactic acid in large quantities, but it’s typically not responsible for the majority of a wild ale’s lactic character. That’s because Lacto is highly sensitive to iso-alpha acids, the hops-derived compounds responsible for a beer’s bitterness. In addition to supplying bitterness, these substances also possess antimicrobial qualities, which is one of the reasons that hops became so intimately associated with beer.

Lactobacillus works best at temperatures above the normal fermentation range and is present in large amounts on the very barley from which brewers make wort. One can conduct a sour mash to take advantage of naturally occurring Lacto to create styles such as Berliner Weisse, and lager brewers who need to lower mash pH but wish to remain compliant with the Reinheitsgebot can allow the native Lacto to sour a portion of the mash before lautering.

Pediococcus is similar to Lactobacillus in that it delivers copious amounts of lactic acid. Unlike Lacto, though, Pedio is a slow worker, taking months to do what Lacto can do in a few days or weeks. The advantages of Pedio, however, are that it is less sensitive to hops and can work at lower pH levels than Lactobacillus. Thus, the majority of the lactic acid character found in wild and sour ales typically comes from Pediococcus.

The major disadvantage of Pedio strains is that they produce appreciable diacetyl, an undesirable butter-like flavor. Fortunately, Pediococcus is almost always used alongside Saccharomyces and Brettanomyces, which can usually degrade diacetyl into less offensive compounds. Pedio also has the potential to build a harmless but disgusting slime on top of fermenting wort. As is often the case with these things, if you ignore it, it usually goes away.


Lactobacillus and Pediococcus are available in numerous strains, but Lactobacillus delbrueckii and Pediococcus damnosus are the most widely used pure strains among hobby and professional brewers who don’t maintain proprietary mixed cultures.

It’s a Wild World

Brettanomyces, Lactobacillus, and Pediococcus may form the holy trinity of wild and sour ales, but these are by no means the only bugs of interest. When you taste notes of vinegar, for example, you have Acetobacter to thank, for it produces acetic acid. Most breweries try to keep Acetobacter out of their mixed cultures, but when used judiciously, the results of an Acetobacter fermentation can be impressive. The sharp acetic character that separates a Flanders red from a Berliner Weisse is due to the activity of Acetobacter.

Other bugs that may or may not be present in varying amounts, especially in classic lambic fermentations, include Enterobacter and Kloeckera, but these typically play second fiddle to the wild yeasts and lactic-acid bacteria responsible for the pleasantly puckering personality of wild and sour ales.

From good old-fashioned Saccharomyces to Pediococcus, brewing bugs exert an influence that’s well out of proportion to their actual size. It takes time, practice, and even a bit of luck to learn how to best connect with these microbes, but as in any good relationship, the potential rewards are anything but sour.

From Berliner Weisse to Gose and points in between, quick souring is rapidly becoming the time-constrained brewer’s choice for building pleasant tartness on a schedule. In Craft Beer & Brewing Magazine®’s online course, Quick Souring Methods, Funkwerks Cofounder Gordon Schuck explains how to use Lactobacillus bacteria, experiment with sour mashing, test acidity levels, and more. Sign up today!