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