For all its history, beer has lived with the curse and blessing of acidity. In most places today, sour beers are a minor specialty, but when they’re balanced and aromatic, they can be among the best and most complex experiences any beverage can offer. When out of control or in the wrong context, acidity, and all that comes with it, is a debilitating flaw.
We often assume that all beers in earlier days were sour to some degree or another, but the ancient Egyptian saying, “May you have bread that never goes stale, and beer that never goes sour,” states otherwise. In the days of epic oak-aged English October beers, a quality called “stale” was prized, but the old books are filled with gruesome remedies for sour beer, including things like cow dung and crab eyes. With popularity of wild and sour beers currently zooming, it seems like a good time to take a look at how to approach them.
Beer is always acidic, even when it doesn’t seem particularly sour. Malting, brewing and fermentation all bring the pH down; conventional beer ranges from pH 3.7 to 4.1. Since pH (a measurement of the concentration of positively charged hydrogen ions, or protons, in solution) is a logarithmic function, each number (from neutral 7 to slightly acidic 6, for example) represents a tenfold change in acidity or alkalinity. Conventional beer can be a thousand times (i.e. 103 times) more acidic than neutral water (pH 7.0), and despite the numbers, really doesn’t taste all that sour to us. Of course, sour beer pH is lower still: from 3.1 to 3.7. At the lower end of that range, nearly 10 times as acidic than conventional beer and 10,000 times as acidic as neutral water, the acidity can be quite piercing.
Sour beers are only partly about acidity. Hundreds of wild yeasts and bacteria can live in beer, all of which produce aromatic compounds that shape the character of sour beers (and ruin conventional ones). Each has different environmental and nutritional needs: oxygen, sugar, starch, temperature, alcohol, choice of substrate and others. These can be used to manage the microbes’ activity.
As a reader of this magazine, you are likely familiar with the main styles of wild and sour beer. Here’s a brief overview:
Spontaneously Fermented Beer, Including Lambic
These beers are meant to ferment entirely from local microflora and can still be made that way. These wild fermentations can be aided by the use of yeast, by re-pitching previous successful cultures or fermenting in inoculated barrels. The most complex and unpredictable of all beers, they may take years to produce. Hundreds of different microbes have been found in lambic, producing a wide range of aromas as well as acidity. They are generally blended to ensure a consistent final product.
Blended Oak-Aged Sour Beers
This includes the famous red and brown (oud bruin) beers of Flanders, but also includes proper English old ales. Batches of beer are aged for an extended period of time, usually in oak foudres (large tanks), where they acquire some wild aromatic fermentation character and often a good bit of acidity as well. This soured beer is traditionally blended into fresh beer, with the soured beer accounting for between 10 and 25 percent, making a mellow, tart and refreshing beer with a sweet-and-sour flavor profile. Brettanomyces plays an important role and Acetobacter typically adds a vinegary aroma and tartness.
Lactic Sour Beers
This is the method most associated with the large family of wheat-based beers, including Berliner weisse, gose, lichtenhainer and others. Historically, these often were brewed without being boiled, sometimes used hops in the mash, and often were filled into casks containing active Lactobacillus cultures from previous batches. Produced in this manner, these have an extremely short life before becoming too sour to drink. These days, a technique called kettle or quick souring is popular. A normal mash is made, lautered into the kettle and allowed to sit at elevated temperatures, sometimes with a blanket of carbon dioxide, for 12 to 48 hours, during which Lactobacillus creates a useful amount of acidity. Aromas tend to be simple and lactic.
Brettanomyces, Saison, and Similar Beers
Once pretty well limited to the Trappist classic, Orval, these have become popular specialties, sometimes fermented entirely with Brett. Aromas are highly dependent on the recipe and the specific strain of Brett. Because this wild yeast is not a big acid producer, any acidity expresses itself as a slight sharpness rather than a full-on sour.
Now, let’s focus on the flavors.
First, acidity. A beer’s acidity is an important characteristic to be controlled by a brewery for a specific product. pH may dispassionately measure acidity, but different acids present different sensory characteristics: soft, creamy, sharp, raspy. What’s the right amount of sour? It’s highly dependent on the style and everything else that’s going on in the beer, but it’s not a drag race. More is not always better. I’ve heard stories of some of the revered masters of lambic complaining that many Americans are looking for a heap of acidity rather than balance, ignoring lambic’s subtler charms.
Huge differences in character come from the byproducts of biochemical activity, differing from bug to bug. There are hundreds of aromatic chemicals ranging from delightful to gag-response-generating. Whether they are good or bad depends on intensity, style and the context of a particular beer. A detectable quantity of any of these would be a fatal flaw in a lager, for example. With regard to wild and sour beers, I hear a lot of people using the term “funk,” but it’s not a particularly useful term or desirable characteristic. Much better to break it down into as specific an aroma as you can.
Many acids bring their own aromas. Lactic acid, produced by Lactobacillus and Pediococcus bacteria, presents a soft, rich, yogurt-y aroma, much prized in Berliner weisse. It’s present in lambic and other sour beers, but may be overwhelmed by more powerful aromas. Acetic is the vinegar acid, produced from alcohol by a group of Acetobacter bacteria that must have access to oxygen, which is why it’s so prevalent in wood and so rarely contaminates beer fermented in stainless steel. While present in lambic, it’s usually more prominent as a slight pickle or vinegar aroma in Flemish sour reds and browns. In small amounts it’s incredibly refreshing; too much and it can be a bit annoying. Again, balance is crucial.
The aromas in sour and wild beers encompass a wide range of chemical types. Various strains of Brettanomyces produce a wide range of aromas, most noticeably a phenolic compound called 4-ethylphenol that is the classic “horsey” or “barnyard” aroma. Some strains contribute an artificial pineapple aroma, an ester called ethyl butyrate. A group of heterocyclic compounds, especially a group of pyridines, add persistent mousy aromas that have a lot less charm than horsey/barnyard notes do. Ethyl acetate is also common, especially in Flemish reds. In balance, it adds a pleasant fruitiness, but when it reaches a certain concentration, it changes into a solvent-y, nail polish aroma that often seems to fill your face with fumes. Fusel alcohols may contribute spicy or hot alcoholic notes.
Oak may bring vanilla and woody aromas and tannic mouthfeel to many of these beers, as well as serving as a substrate for microbes and allowing easy access to oxygen.
Because many of these beers have extended aging, we find aromas specific to changes happening over the course of months or even years. Just like sherry, wild beer can oxidize in various ways. Oxidation may also reverse the process through which yeast creates alcohol in the first place, turning it back into acetaldehyde with nutty, chalky, yeasty overripe apple, and in large quantities, solvent-y aromas.
Over time, the dead yeast falls apart, releasing its components into the beer and releasing flavors and aromas. This can add a pleasant toastiness, but also can produce garbage or bad-breath type aromas due to a chemical called mercaptan. Now that’s funky.
So what to look for? A great sour beer is like a layer cake: Icing is great, but too much and it’s just an overbearing mess. So it is with the acidity and wild aromas of sour beer. In the right balance, they’re a rich counterpoint to the underlying beer. Too much is simply, well, too much. Finely balanced with everything working harmoniously, they are one of the wonders of the beer world. Bartender, pour me a slice.
This story appears in the September 2016 issue of All About Beer Magazine. Click here to subscribe.
Randy Mosher is the author of Tasting Beer and is a senior instructor at the Siebel Institute.