Back before the age of modern refrigeration, sanitation and the understanding of how bacteria worked, it would be safe to say that most of the beers that people drank had some level of sourness to them. A sour flavor can be considered an unwanted flavor in modern beer styles and is sometimes a sign of some kind of infection. But there are several styles where that level of acidity is normal and is intentionally created in the beer.
Classic sour styles include the German Berliner Weisse and Gose, Belgian Oud Bruin, Flanders Red, and Lambics such as Kriek or Gueuze. All of these styles feature a lactic tartness from Lactobacillus with the Belgian versions often exhibiting some acetic character derived from barrel aging. New World Sours, as some people call them, have come onto the scene with the rise of craft beer and are quickly becoming one of the fastest growing segments in the industry. These beers often contain unusual ingredients, can be aged in a variety of wine barrels, and some are even successful spontaneously fermented beers.
Sour beers get their unique flavors from acid-producing bacteria, primarily Lactobacillus and Pediococcus. Sometimes these are naturally occurring, but more often they are intentionally added in a controlled environment. Lactobacillus can ferment with or without oxygen and produces lactic acid which creates a soft and mild tangy acidity similar to lemon juice. This is also the bacteria that is used to make many cheeses, as well as yogurt. Pediococcus adds a richer, more complex sourness and ferments sugar into lactic acid but does not produce carbon dioxide. The whole process can be fairly unpredictable, so blending different barrels is a very important part of the finished product.
Beers fermented with the wild yeast, Brettanomyces, are often incorrectly called “sour beers”. It is not a souring organism and does not create lactic acid, which is required for a sour beer. Brettanomyces, or Brett for short, creates more floral, fruity, earthy and sometimes barnyard or funky aromas and flavors. Beers brewed entirely with Brett can often exhibit apricot, pineapple and other tropical fruit aromas. Phenols will often have a clove, honey or even medicinal aroma. In the hands of a skilled brewer, Brettanomyces produces incredibly complex and unique flavors and aromas.
Gose (pronounced “go-zuh”) and Berliner Weisse have both seen recent revivals in the U.S. craft brewing scene. While both are German wheat ales that are soured by Lactobacillus, they each have their own unique characteristics. Gose – which gets its name from the town in which it was first created, Goslar – is made with salt and coriander. Those flavors should be subtle, as is the level of sourness in this highly refreshing beer.
Berliner Weisse, from Germany’s capital, expresses more acidity, but is even lower in alcohol (traditionally between 2.8 and 3.8% ABV) than Gose (4.2 to 4.8%). When served in bars and restaurants, Berliner Weisse is often served “mit schuss,” or “with a shot” of woodruff or raspberry syrup. American brewers have taken to short-cutting this step by making fruited variants in the brewery
Flanders Red and Oud Bruin start as near-identical base beers, but one significant difference results in two styles: Oud Bruins ferment and age in stainless steel, while Flanders Red does its thing in oak. This gives the Flanders Red a similar flavor profile to red wine, although with more sour character, while the malt shines through more in an Oud Bruin.
Another style from Belgium is the Gueuze. This style is known for its high level of effervescence, the result of extensive (often two-plus years worth) bottle conditioning. Gueuze, a form of Lambic, blends spontaneously fermented beers of various ages, with the younger beers providing sugars for refermentation in the bottle.
Anderson Valley Brewing makes a series of Goses, some made with watermelon or blood orange. The Bruery, also from California, is well-known for its various sour ales, including a Berliner Weisse, Gueuze, and sour Stout. Internationally, Lindemans from Belgium is perhaps the best-known sour ale producer, starting with their Fruit Lambics. From Germany, Bayerischer Bahnhof makes a high-quality, widely available Gose and Berliner Weisse.