Infected beer is bad. Very bad. Drain pour beers are the worst. It’s not just money down the drain, but it’s a big let down with a beer you’ve been looking forward to drinking. You may be able to finish a beer with some off flavors, like a slight diacetyl or skunky flavor, but not an infected beer.
Infected beer almost always indicates a sanitation problem. Acetobacter, Lactobacillus and Pediococcus are the primary culprits. These bacteria are everywhere and their mission is to ruin your beer. Acetobacter creates Acetic Acid, which give the beer vinegar aromas and flavors. Lactobacillus and Pediococcus produce Lactic Acid, which make beer sour, and not in a good way.
Infected beer can happen to anyone. I’ve noticed it mostly in homebrews (fyi, judging homebrew competitions isn’t as fun as you think). A lot of bacteria can sneak in during bottling, especially if you do bottling in the kitchen where most home brewers do. Homebrewers, your kitchen is one of the biggest bacterial playgrounds in your home. However the professionals aren’t immune. I’ve had infected bottles and cans from craft brewers who usually make great beer.
Of course, some beers are intentionally infected, using bugs like Brettanomyces, a type of wild yeast, and even bacteria like Lactobacillus and Pediococcus. But there is a big difference between an infected Pale Ale and Cantillon Gueuze, but that’s a post for another day.
If you get an infected beer at a bar or store, let the staff know right away. Take it back and ask for a fresh beer.
I hope you’ve enjoyed this series of post on beer off-flavors. Here’s to fresh, delicious beer!