Wild & Sour Beers

Wild & Sour Beers

With a resurgence of interest in wild and sour beers from breweries and drinkers alike we decided to put together a post on some of the styles available and how they are made. We hope it enables you to know your Gueuze from your Gose and your Lactobacillus from your Pediococcus.

What is a sour/wild beer?

“Wild beer” is beer that has not been fermented with an isolated yeast strain like most pale ales or lagers are, but rather with “wild yeast” – an umbrella term for the vast number of yeast strains present in the air that surrounds us. In a way these beers are the closest to wine, in the sense that they reflect their terroir – the characteristic taste and flavour imparted to a wine by the environment in which it is produced. “Sour beers” are beers that are intentionally soured, often at the beginning of the brewing process by the use of bacteria, commonly Lactobacillus.

The main difference between various sour and wild beer styles is the brewing process. There are two main ways of brewing a wild or sour beer – either to let it ferment spontaneously (e.g. Lambic) or to purposely infect it with specific souring bacteria (e.g. Berliner Weisse, Gose & Flanders Red).


Traditional lambic beers are made by transferring the freshly boiled wort (typically one third raw wheat and two thirds malted barley) into open vessels called “coolships”. These are large and shallow in order to maximise the wort’s surface contact with yeast and microorganisms present in the air in the room. The rooms often have wooden ceilings that harbour the mix of bacteria and yeast unique to the brewery.

After the wort has been left to cool overnight, it is transferred to oak or chestnut barrels. At this stage the beer contains all the sugars that were extracted from the grain by mashing. It is then left to age for up to three years; the older the lambic is, the dryer it will become.  Straight lambic is somewhat rare – it can be found in cafes in and around Brussels, but is not regularly exported. On the other hand, Gueuze – a blend of one, two and three year old lambics – is widely available in the UK.  Gueuze undergoes a secondary fermentation in the bottle, giving it a Champagne-like quality and is sometimes dubbed the “Champagne of Brussels”.

Berliner Weisse

In contrast to lambics, the brewing of Berliner Weisse is a controlled process in which a wheat beer is intentionally infected with Lactobacillus bacteria, either at the point of mashing (“sour mash”) or at the kettle after wort has been sterilized. The latter is the approach taken by Beavertown Brewery for their Phantom series and brewer Tiago was kind enough to explain the brewing process to us:

“We sour our Berliner Weisse in the kettle – we mash barley and malted wheat normally and then transfer the wort into a copper kettle. Here we bring the temperature to 80 degrees to sterilize it and to make sure there isn’t any unwanted yeast or bacteria present in the wort. Then we let it cool to 40 degrees – the ideal temperature for Lactobacillus. We pitch the bacteria and leave it to work for 24 hours. In this time Lacto will have produced mostly lactic acid and a little bit of ethanol and the PH of the wort will be around 4.4. When the wort is sour enough, we bring it to boil to sterilise it, which will get rid of Lacto. Then we transfer it into fermentation vessel and ferment it with a regular, clean strain of US yeast and also add some hops (not for the flavour but for their preserving qualities). At this point we also add the lemon juice. After the fermentation is over, we transfer the beer into a secondary fermentation vessel, where we add the fruit – dried lime, yuzu, rhubarb, depending on which of the Phantom beers we are making. Here the beer undergoes a secondary fermentation as the yeast begins to convert the sugars contained in the fruit. “

Souring bacteria and wild yeast

Brettanomyces Bruxelles is the most famous wild yeast and among many beer geeks it has an almost cult status. It imparts a funky flavour to beer – often described as reminiscent of “wet horse blanket” or “barnyard”. A very aggressive strain of yeast, “Brett” will continue fermenting until it converts all the sugars in the beer into alcohol – where a regular yeast stopped ages ago, Brett is still at work. This makes bretted beers perfect for aging – they become very dry and the flavours develop and become more pronounced over time.

Brett is a major component of lambic breweries, – one of the most highly regarded being Cantillon. Beer lovers go crazy for their beers, and there is good reason for it. No other beer will ever taste like theirs, simply because of the character of the brewery and the yeast and bacteria it has been harbouring for over a hundred years. They are typically sour, earthy, musty & savoury – though really they must be tasted for their appeal to be fully understood. Other great lambic breweries include Girardin, 3 Fonteinen & Boon.

On the other hand, bretted beer can be produced to a brewer’s recipe. This is often done by simply pitching the yeast in the beer after the primary fermentation, though 100% Brett fermented beers are also made. Modern Brett beers worth trying include Yeastus Christus IPA from To Ol, U.S. Alive from Mikkeller & Siren’s All Bretts are Off.

Lactobacillus is the most common souring bacteria used in brewing. It is prized for its ability to produce sour flavours without any unwanted funkiness. Outside of brewing you’ll find it at work in things like yoghurt and pickles. Along with Pediococcus it is responsible for all those lovely, refreshingly tart Berliner Weisse around at the moment as well as Gose, a similar style of Leipzig origin with added salt and coriander. Modern Berliner Weisse is often dry-hopped – Siren’s Calypso is a great example, as well as Redchurch’s Tartelette and the aforementioned Phantom series from Beavertown. Interestingly, you’ll find it hard to source a Berliner Weisse in Berlin or a Gose in Leipzig – these beers are almost extinct or drunk sweet, with a shot of syrup and a straw.

Also commonly used in brewing is Acetobacter, which produces acetic acid – yes, vinegar! The most notable exponent of this style is Flanders where a range of sour red and brown ales are produced, the former often referred to as the ‘Burgundies of Belgium’.  Flanders Red ale is aged in oak barrels that harbour Acetobacter for up to three years. Brewers can control the levels of acidity by restricting the amount of oxygen available to the bacteria. Probably the most famous brewer of these beers is Rodenbach – their Grand Cru (a blend of young and older beer in 1:2 ratio) is the most common, however they produce a whole range of different blends and Vintages. Keep your eyes peeled for a 2012 vintage especially. The late beer writer Michael Jackson gave the Grand Cru title of a “World Classic”. In the UK a similar style is produced by Wild Beer – try the Modus Operandi or its barrel aged version, Beyond Modus.

A few to try:

Bahnhof Gose
Almanac Gose
Redchurch Tartelette
Cantillon Gueuze
Girardin Kriek

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Published on by YKWX.