Sour beer
Beer intentionally made acidic, tart, or sour.
Sour beer is defined by its intentionally acidic, tart, or sour flavor. Common styles include Belgian lambics, Flanders red ale, German Gose, and Berliner Weisse. In contrast to modern brewing, which relies on a sanitary environment to prevent wild yeast contamination, historical brewing often involved a starter that naturally contained some wild yeast and bacteria. To create a sour beer, brewers deliberately introduce wild yeast strains or bacteria, traditionally through the barrels or by cooling the wort in an open coolship exposed to outside air. The bacteria Lactobacillus and Pediococcus are the most common microbes used for souring, while the fungus Brettanomyces can also contribute acidity. Adding fruit directly provides organic acids like citric acid, and tartness can also be achieved by adding acid directly or using large amounts of acidulated malt. The use of wild yeast can make fermentation unpredictable, sometimes taking months and requiring years to mature, though modern kettle souring methods can produce sour beer in just a few days, similar to typical ales. While any beer can be soured, most follow traditional or standardized guidelines. American wild ales use yeast and bacteria strains instead of or alongside standard brewers yeasts, often without strict style parameters. Berliner Weisse, once Berlin’s most popular alcoholic beverage, is a low-alcohol beer soured with Lactobacillus and typically served with flavored syrups. Flanders red ale is fermented with brewers yeast, then aged in oak barrels, often blended with younger beer for consistency. Gose, originating in Goslar, Germany, is top-fermented with coriander and salt, soured by inoculating the wort with lactic acid bacteria before primary fermentation. Lambic is a spontaneously fermented beer from the Pajottenland region near Brussels, where wort is cooled overnight in a koelschip exposed to winter and spring air, then barrel-fermented and matured; most lambics are blends like gueuze or fruit versions like kriek and framboise, making pure unblended lambic rare. Oud bruin, from the Flemish region of Belgium, is darker than Flanders red ale and not aged on wood, relying on cultured yeasts for its sour notes.
- Abv range
- around 3% abv (Berliner Weisse)
Lore & Background
The most common microbes used to intentionally sour beer are the bacteria Lactobacillus and Pediococcus, while the fungus Brettanomyces can also add some acidity. Another method for achieving a tart flavor is adding fruit, which directly contributes organic acids such as citric acid. Additionally, acid can be directly added to beer or added by the use of unusually large amounts of acidulated malt. Depending on the process employed, the uncertainty involved in using wild yeast may cause the beer to take months to ferment and potentially years to mature. However, modern kettle souring methods allow sour beer to be created within a typical timeframe for ales, usually several days. While any type of beer may be soured, most follow traditional or standardized guidelines. American wild ales tend not to have specific parameters or guidelines stylistically, but instead simply refer to the use of unusual yeasts. Berliner Weisse, at one time the most popular alcoholic beverage in Berlin, is a somewhat weaker beer made sour by use of Lactobacillus bacteria and is usually served with flavored syrups to balance the tart flavor. Flanders red ales are fermented with brewers yeast, then placed into oak barrels to age and mature, and the mature beer is usually blended with younger beer to adjust the taste for consistency. Gose is a top-fermenting beer that originated in Goslar, Germany, characterized by the use of coriander and salt and made sour by inoculating the wort with lactic acid bacteria before primary fermentation. Lambic is a spontaneously fermented beer made in the Pajottenland region around Brussels, Belgium, where wort is left to cool overnight in the koelschip exposed to the open air during winter and spring, then placed into barrels to ferment and mature. Most lambics are blends of several seasons’ batches, such as gueuze, or are secondarily fermented with fruits, such as kriek and framboise. Oud bruins, originating from the Flemish region of Belgium, are differentiated from Flanders red ale in that they are darker in color and not aged on wood, and this style tends to use cultured yeasts to impart its sour notes.
Reader's Guide
Sour beer represents a traditional approach to brewing that predates modern sanitary methods, relying on wild yeast and bacteria to create distinctive acidic flavors. The style encompasses a diverse range of regional traditions, from the spontaneously fermented lambics of Belgium's Pajottenland region to the salted and spiced Gose of Germany. Berliner Weisse was once the most popular alcoholic beverage in Berlin, while Flanders red ales and oud bruins showcase the Flemish sour tradition. American wild ales have expanded the category by using unusual yeast and bacteria strains without strict stylistic guidelines. The production methods vary widely: some sours are aged in oak barrels for months or years, while modern kettle souring can produce a sour beer in days. Many traditional sours involve blending, such as lambic blends like gueuze or the practice of blending mature Flanders red ale with younger beer for consistency. The use of fruit, spices, or salt in some styles further diversifies the category. Sour beer's legacy is tied to historical brewing practices that embraced rather than excluded wild microorganisms, and it continues as a globally recognized beer family with both traditional and innovative expressions.
Did You Know?
- Berliner Weisse is usually around 3% abv and often served with flavored syrups.
- Lambic is spontaneously fermented in the Pajottenland region around Brussels, Belgium.
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