Sour beer isbeer which has an intentionallyacidic, tart, orsour taste. Sourbeer styles include Belgianlambics andFlanders red ale and GermanGose andBerliner Weisse.
Unlike modernbrewing, which is done in a sanitary environment to guard against the intrusion of wild yeast,[1] historically the starter used from one batch to another usually contained some wild yeast and bacteria.[2] Sours are made by intentionally allowing wild yeast strains or bacteria into the brew, traditionally through the barrels or during the cooling of thewort in acoolship open to the outside air.[3][4]
The most common microbes used to intentionally sour beer are the bacteriaLactobacillus andPediococcus, while the fungusBrettanomyces can also add some acidity.[1] Another method for achieving a tart flavor is adding fruit, which directly contributes organic acids such ascitric acid.[4][5] Additionally, acid can be directly added to beer or added by the use of unusually large amounts of acidulatedmalt.
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.[1] However, modern kettle souring methods allow sour beer to be created within a typical timeframe for ales, usually several days.[6][7]
While any type of beer may be soured, most follow traditional or standardized guidelines.
Beers brewed in the United States utilize yeast and bacteria strains instead of or in addition to standard brewers yeasts. These microflora may be cultured or acquired spontaneously, and the beer may be fermented in a number of different types of brewing vessels. American wild ales tend not to have specific parameters or guidelines stylistically, but instead simply refer to the use of unusual yeasts.
At one time the most popular alcoholic beverage inBerlin, this is a somewhat weaker (usually around 3% abv) beer made sour by use ofLactobacillus bacteria. This type of beer is usually served with flavored syrups to balance the tart flavor.[8]
Flanders red ales are fermented with brewers yeast, then placed into oak barrels to age and mature. Usually, the mature beer is blended with younger beer to adjust the taste for consistency. This is also sometimes referred to as "flemish red".[9]
Gose is atop-fermenting beer that originated inGoslar, Germany. This style is characterized by the use ofcoriander andsalt and is made sour by inoculating the wort withlactic acid bacteria beforeprimary fermentation.
Lambic is a spontaneously fermented beer made in thePajottenland region aroundBrussels,Belgium. Wort is left to cool overnight in thekoelschip where it is exposed to the open air during the winter and spring, and placed into barrels to ferment and mature. Most lambics are blends of several seasons’ batches, such asgueuze, or are secondarily fermented with fruits, such askriek andframboise. As such, pure unblended lambic is quite rare, and few bottled examples exist.
Originating from theFlemish region of Belgium,oud bruins are differentiated from the Flanders red ale in that they are darker in color and not aged on wood. As such this style tends to use cultured yeasts to impart its sour notes.
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