The first time you brew a wild or sour beer, you may be surprised at what shows up in your fermentor. In fact, go ahead and run a Google image search on “beer pellicle.” I’ll wait.
Eww, right? A pellicle (pronounced “PELL-uh-kull”) is the gooey, slimy, bubbly, fuzzy layer of nastiness that may appear on the surface of beers fermented with Brettanomyces, Lactobacillus, or Pediococcus. It’s a type of biofilm, which is a colony of microbes that huddle together and float like a raft on the surface of certain kinds of beer.
If you intentionally inoculate beer with Brett, Lacto, or Pedio, then pellicle formation is a sure sign that wild and sour bugs have established themselves in generous numbers. Pellicles don’t form on beer fermented with straight up Saccharomyces, though, so the presence of one may be an indication of contamination (also called an infection).
Pellicle development isn’t, however, guaranteed, even in the most funky of ales. Some beers get one and others don’t. Whether a beer develops a pellicle or not has little to no bearing on the nature or quality of the end product. It’s largely a cosmetic feature that is fun to look at, one that may possibly fuel a nightmare or two about microbes taking over the planet.
So what exactly does a pellicle do? Your guess is probably as good as mine. Most brewers view pellicle formation as a sign that oxygen has infiltrated the headspace and that the yeasts and bacteria that collect in the pellicle do so in order to gain access to that oxygen for aerobic metabolism. But it’s not entirely clear what prompts pellicle development in one beer and not in another.
There is one practical piece of information, though, that you can put to use in your sour-beer brewing. Michael Tonsmeire notes in American Sour Beers that pellicles may provide some protection against contamination from Acetobacter, a bacterial species that most of us want to keep at bay. He notes that aging sour beer in a vibration-free location will minimize disruption to the pellicle and thus enhance the protective properties it conveys. So, use that basement if you have one, and avoid keeping your sour beer near the washing machine.
The photo accompanying this article is of a wild beer and its pellicle, currently aging in the Craft Beer & Brewing offices. If you have a photo of your favorite pellicle, we’d love to see it.
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 CBB’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!