Sour beers started off as, well ... sour! Before modern fermentation and brewing processes, bacteria and wild yeast strains snuck their way into brewing vessels - usually hitching a ride with stirring utensils or setting up shop within the vessel itself from exposure to the surrounding air. Just as we unknowingly introduce beneficial microbes into our body day-to-day, the introduction of these stealthy strains were creating magic (uncontrolled magic, but magic nonetheless). Unfortunately beer drinkers didn't see it this way at the time, and after the development of more controlled fermentation techniques, most sour beers disappeared and were replaced with balanced ales and lagers. Lucky for us, sour beers started to make a comeback around the 1970’s and look as though they're here to stay.
The process of brewing and the stage at which bacteria enters the picture is important. First, malted grains are ground up, mixed with water and heated in a process known as “mashing”. This process activates enzymes responsible for converting the grain starches into sugar, which is essential for fermentation. The sugary liquid (or the wort) is collected and then boiled, and at this stage hops and other ingredients (such as fruit or spices) are added for flavor. Once the wort has cooled, bacteria and yeast are added in and get straight to work. As bacteria and yeast consume the wort sugars, carbon dioxide and alcohol are produced. Once this mixture goes through a barrel or bottled based aging process, the end result is beer!
In the past the word “bacteria” was almost always associated with a pathogen or virus, however as we’ve learned in the modern day microbial world, bacteria are our friends - especially if you’re a sour beer fan. The most common types of bacteria used in sour beer production are Lactobacillus and Pediococcus. Lactobacillus is a very established and widely utilized bacterial strain that is found in yogurt and fermented/pickled vegetables (think kimchi and sauerkraut). When Lactobacillus consumes sugar, it produces lactic acid instead of alcohol, which contributes to the sour taste of the beer. Similarly, Pediococcus produces lactic acid versus alcohol, causing the overall pH of the beer to lower and result in a tart taste. While these two strains elicit similar effects, they are not apples to apples. Think of Pediococcus as your friend who rarely showers, has a salty personality and can be full of surprises - as it has been known to have a harsher bite and can introduce a variety of unknown smells (like one reminiscent of sweaty socks!).
The use of microbes in sour beer is just one example among thousands that show how diverse microbial function is. Next time you go to grab a beer, think sour!
Glossary Of Terms:
Fermentation: A process in which yeast and bacteria consume sugar to produce carbon dioxide and alcohol
Bacteria: Single celled microorganisms
Yeast: A single celled microorganism classified as a fungus
Enzyme: A biological catalyst that accelerates cellular processes
Pathogen: A type of bacteria or virus that cause infection or disease