The inception of my sciencey articles happened over beers one night at Falling Rock Taphouse. At the time we were drinking Russian River’s Consecration, one of the really excellent American sours out of Santa Rosa, California. It is rich, fruity, and awesome. Foremost on the palate though is its tartness. Brightly sour, it dries out the sides of your tongue and really perks up your taste buds. The question recently came up: Why are sour beers sour? Well, we need to talk about succession, metabolism, and microorganisms.
Sour, one of our five basic tastes, is generally associated with acids or acidic foods. Common fruit-based acids like citric acid or malic acid should be familiar to us, as they are in tons of the things we eat. They are found in nature in fruits. Citric acid you should know, but malic acid might be unfamiliar to you. It is the main souring agent dusted on the outside of a Sour Patch Kid. Yum. The name is taken from the Latin word for apple and is very apparent in the tartness of a Granny Smith. It is important to mention this here because it is very prevalent in grapes and is present in wine.
During wine making, some makers desire a softer acid profile and in the process of malolactic fermentation will add lactic acid producing bacteria (specifically Oenococcus onei) which decarboxylates malic acid into lactic acid. Any of you who are as familiar with Warheads sour candy as I am can tell you how sharp and bitingly sour that malic acid is. Lactic acid generally has a much lighter sourness. You could probably discuss the difference between “sour” and “tart” here if you would like. I will wait.
Done? Good, let’s move on.
Sour beer is a bit of a catch-all term for beers that are sometimes spontaneously fermented (Lambic, geuze, etc.) or intentionally infected (Avery, Russian River, etc.) with a culture of various yeasts and bacteria to achieve a sour, vinous, and generally funky palate of interesting flavors not normally associated with beer. My dad hates the stuff. You can expect lactic acid tartness to give it a bright refreshing aspect. Flavors contributed by Brettanomyces species offer “barnyard,” “horse blanket” or “goaty” flavor. I know, this sounds awfully nasty but if you think about it these descriptions offer lovely suggestions of beautiful organic things. They hardly ever taste like manure.
Acetic acid is another acid that is notably present in sour beers. Acetic acid is the base flavor component and souring agent of vinegar. I personally like a sour beer with a strong presence of this acid. It seems to go well with a heavy fruit like you will find in a Kriek, a traditional Belgian beer aged with cherries. This is produced by Acetobacter and other genera of acetic acid bacteria feeding on a small amount of the ethanol in the beer.
These and many other metabolic products make up a “sour” beer. Esters, acids, phenols and other volatile organic compounds. They are often barrel aged with fruit and take on flavors there as well.
The most interesting things about most sour beers is that it takes a whole village of microorganisms to complete the beer. In a traditional, spontaneous fermentation, vents are opened to the night air and the yeasts and bacteria begin to ferment the beer. Later during aging, others take over. Essentially, one group makes the young beer suitable for the next group to take over. It starts with enterics, related to Escherichia coli who get things going and produce some funky tastes. This is happening in conjunction with the growth of Saccharomyces (brewing yeast) species. They gobble up the easily fermentable sugars and give way to lactic acid producers such as Pediococcus damnosus that produces lactic acid from glucose metabolism. The general consensus is that as the primary fermentation ceases, Brettanomyces takes over as the most populous and active organism.
Aging can continue for years at this state, letting Brett. species chew away at the dextrins and other goodies. As time goes on, Brett. sp. will also form a pellicle, which is a bizarre layer of polysaccharides that would gross you out if you are not a brewer or a microbiologist. Luckily, I am both. I love the creepy stuff.
This is interesting. Pediococcus likes an environment with no oxygen. So the longer the beer ages and gets more and more inhospitable, Pedio. fires back up providing a bit more sour funk.
This basic model comes from the traditional Belgian style. It easily illustrates some of the complex intricacies that are involved. I even left out the blending process! In modern breweries, tradition has been tossed out the window a bit. Each of these organisms has been isolated and played with. Sour beer had a bit of a surge in the last few years and continue to be some of the most sought after releases from breweries around the world. If you haven’t had one do yourself a favor and go get some. La Folie from New Belgium is iconic and delicious and Russian River Brewery has what some consider to to be the best examples in the world. This topic could go forever and has many studies analyzing it. I have barely scratched the surface here. I suppose you don’t need to know everything, just tip your glass to the rad little guys that got the beer to where it needs to be!
Tags: acetic acid, Acetobacter, Brettanomyces species, Consecration, Escherichia coli, Falling Rock, la folie, malic acid, New Belgium, Oenococcus onei, Pediococcus damnosus, russian river, Saccharomyces, science, sour, sour beer, tart