In the past years, sour beers gained popularity among beer geeks. And we’re not talking about an accidental acidic taste that’s the result of a brewing or packaging mistake. But that is how it originally started.
In fact, until the end of the 19th century sour beers were more widely spread over Europe. In those times all beers were a little sour. Acidulating fungi and bacteria were not known, and the brewers were not aware where the sour side effect came from.
Thanks to technological and scientific developments (e.g. pasteurization and sterilization) the brewing process and fermentation can be now fully and safely supervised. Now breweries are able to create sour beers, according to certain specifications and controlled methods.
What makes a beer sour?
The short answer is: bacteria and/or wild yeast. Hops are only used for preservation, so mostly aged hops are added.
Wild yeast
A famous wild yeast strain is Brettanomyces (Brett), which was first discovered on fruit skin. It is generally used in combination with ale or lager yeast. Brett converts the sugar chains that normal yeast can’t, while it creates plenty of esters and phenols. If used under the wrong circumstances, Brett can spoil your beer with unpleasant flavours, reminiscing medicine, barnyard or even smoked ham. But under good hygienic conditions and a well-controlled temperature it gives very nice esters and a funky earthiness.
Bacteria
There are two kinds of bacteria that you can find in yogurt, or in other milk and food products. Lactobacillus creates lactic acid by transforming sugars that normal yeast can’t. Pediococcus is able to work without oxygen, deepening the sourness. Brewers have to be very careful which strain to work with, control the temperature and keep pH at optimal level, to get a unique sour flavour. Otherwise an undesired acidic taste can be produced.
Examples
Because the methods – at least partly – rely on a natural process, the outcome is hard to predict. Some use wild yeast, others apply lactic bacteria and you can even combine the two. They will result in different flavours, aromas and beer styles. Here are some popular examples of sour beers.
American Wild Ale
The name says it all. American Wild Ale is brewed in the United States. They are similar to Belgian sour beers, and are typically fermented using a strain of Brettanomyces, resulting in a funky flavour.
Berliner Weisse
This hazy white beer is a traditional sour ale from – you guessed it – Berlin. Its sourness comes from Lactobacillus bacteria and it is one of the most acidic sour beers. Therefor it is sometimes consumed with fruit syrup in Germany. Low ABV (3-3.5%), high carbonation and tart mouthfeel makes it a refreshing choice, especially in the summer months.
Brett Beer
This beer is fermented by a combination of wild yeast, ale yeast and Brettanomyces. The result depends on the malt-hop balance, the length and method of aging, and the variation of wild yeast. Flavours are described as fruity, earthy or musty depending on the specific strain used.
Flanders Red Ale
The name of this “wine-like” beer refers to its colour and the origin (West Flanders, Belgium). The fermentation starts with normal brewer yeast, but then comes the magic: the beer is aged in oak barrels for 1-3 years. The barrel-aging with lactic acid bacteria and yeast helps to create a pleasant tartness, fruity flavours and tannins. It is often blended with a younger beer to balance the flavour.
Flanders Oud Bruin
Comparable to Flanders Red Ale, but the maltiness and colours are much deeper and the acidity is lower. It is not aged in wooden barrels, but in steel casks for at least a year. The sour flavour is a result of cultured yeast and bacteria. The barrel-aging develops dark fruit (plum, cherry) notes, while the caramel malts bring toffee and nutty hints.
Gose
This traditional German beer comes from Goslar. In the old days this beer was fermented spontaneously, but today’s craft brewers mainly use normal brewing yeast and lactic acid bacteria. The characteristics are also determined by using sea salt or even sea water. The style was almost forgotten after WWII, but the craft industry thankfully brought it back.
Lambic
It doesn’t get much wilder than Lambic. This sour wheat beer from the 13th century is one of the oldest beer styles in the world. Officially it can only be made in the Zennevallei near Brussels, where more than 80 natural yeasts help to ferment Lambic in the open air. The beer is brewed in the winter and should be aged in oak barrels for at least one year. Sub-styles of Lambic are Kriek (sour cherry), Framboise (raspberry) and Gueuze (a blend of 1 and 2-3 year old Lambic).