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Sour beers are one of the most unusual beer styles, but are naturally intriguing for the homebrewer. They range from a gentle sour tinge that helps provide complexity to ragingly mouth-puckering sourness. The organisms that create sour flavors usually contribute other aromas and flavors that are unattainable with normal yeast, such as the “barnyard” or “horse blanket” flavors associated with some Brettanomyces strains.
Sound unappetizing? Perhaps to some, but there is no denying the complexity, the wonderful balance, and the simple allure of sour beers.A couple of tips for brewing sour beers: First, best practice is to use separate plastic equipment for beer containing souring organisms. Something like a glass carboy or a stainless kettle can be cleaned without any issue, but more porous plastic could potentially harbor the souring bacteria and infect later batches. Secondly, making sour beer takes some patience, as the slow-acting bacteria can take a year or more to provide the level of sourness present in many styles. Many souring organisms prefer small amounts of oxygen as they work, so you can speed up their activity a bit by keeping the brew in a plastic bucket or wooden barrel, either one of which will slowly let in small amounts of oxygen.
For many, sour beer means Belgium. The adventurous brewers of this small nation are definitely the torch bearers of the sour styles, and a direct link to their long traditions. The most famous Belgian sour is the Lambic. Lambics are traditionally made by inoculating the wort with wild yeasts from the air, which generally results in a mixed culture of regular saccharomyces yeast, brettanomyces, pediococcus, and lactobacillus. This results in a complex, wine-like character and a very dry finished beer. Aged, unblended lambics are among the most sour beers.
The Flanders red ale style is similarly intense, but includes some specialty malts that make the color a deep red. Fruit flavors such as plum can often be found along with the characteristic sourness. Oud Bruin (sometimes called Flanders Brown) is even darker and features some maltiness, which is unusual in sour styles. Some caramel flavors and sweetness, as well as fruity notes, can be expected.
Although you can occasionally find Flanders reds and oud bruins with fruit added, the practice is more common with lambic. A lambic with raspberries added is called a framboise, with cherries it is a kriek. The fruit is often added to the secondary fermentor and can remain the in beer for long periods of aging.
German Sour Beers
Germany has a long and celebrated history of sour beers, but few examples have survived to modern times. The most commonly brewed is Berliner Weisse, a very sour, highly carbonated wheat beer. Berliner Weisse is fermented by a blend of normal yeast and lactobacillus, and occasionally brettanomyces as well. The lactic acid character from the lactobacillus dominates, creating a very tangy, tart acidity. Carbonation is normally quite high to provide a very sparkling and refreshing quality. Berliner weisse is sometimes served with fruit or woodruff syrups to cut the acidity.
A very rare and unique beer called Gose is also brewed in Germany. Gose is similar to Berliner weisse in many respects, but also contains coriander and salt. The amount of salt ranges from barely noticeable to quite salty, and the sourness is usually the dominant feature. A mixed culture of normal yeast and lactobacillus is generally used to produce the sourness.
English beers are rarely thought of as being sour, but there is a long history of sour beers in England. Traditionally the “old ale” or “stock ale” that was kept in wooden barrels for long periods of time became slightly soured by bacteria such as brettanomyces claussenii and lactic acid producing bacteria. Beers of very high alcohol and gravity were given fruity, sour characteristics by these organisms. Few modern examples survive, but undeterred homebrewers have made fabulous interpretations of the style.
The Kentucky Common is a final sour beer of note. This beer was brewed in America around Louisville, Kentucky. The brewers used a sour mash technique, where the mash was cooled, inoculated with lactobacillus and allowed to rest at about 100 degrees for a couple of days before draining. Then the mash was brought back up to normal temps, drained and sparged as usual, and the sour liquid boiled, cooled, and given normal ale yeast. The result is a sour, refreshing beer that is rendered slightly dark from a small percentage of roasted grains.