How are Sour Beers Made? An artistic shot of a sour beer with raspberries and strawberries.

How Are Sour Beers Made? A Complete Guide and 9 Beers to Try

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I recently visited Brussels in Belgium and tasted several wonderfully fruity, tangy and sour beers. One flight of beer genuinely looked like a rainbow! But it got me thinking: how are sour beers made? If you’re sitting there sipping a sour beer and wondering the same while pulling the face from the Haribo Tangfastics’ advert, well, look no further. This article will explore sour beers’ superhero origin story, set out the various methods for brewing this sour delight and give you a few suggestions to try next. You in?

The Rise of Sour: History & Origin Story

You may think sour beers are new to the party, but they are among the world’s oldest brewing styles. Sour beer dates back thousands of years but has recently grown significantly in interest and popularity, especially within the craft beer movement. 

Ancient Beginnings

The production of sour beers predates modern brewing techniques, originating from a time when all beers had some degree of sourness. This was primarily due to spontaneous fermentation from wild yeast and bacteria present in the air, which was the norm before Louis Pasteur discovered and understood yeast’s role in fermentation in the 19th century. 

Ancient brewing practices in various regions, including what is now Belgium, Germany, and other parts of Europe, naturally resulted in sour-tasting beers.

European Traditions

We Europeans have always been partial to a bit of beer, and several European countries have long-standing traditions of intentionally brewing sour beers. Notable examples include:

  • Belgium: Famous for its Lambics, Gueuze, Flanders Red Ale, and Oud Bruin, Belgian sour beers are known for their complex acidity, fruitiness, and funky flavours, developed through spontaneous fermentation or the addition of specific wild yeast strains and bacteria.
  • Germany: Known for styles like Berliner Weisse and Gose, which are traditionally tart and sometimes slightly salty. These beers are often brewed with lactobacillus bacteria to achieve their characteristic sourness.

Decline and Resurgence

With the industrialisation of brewing and the rise of lager beers in the 19th and 20th centuries, the production and consumption of sour beers declined significantly. The control over fermentation processes and the preference for cleaner, more consistent beer flavours led to a decreased interest in the unpredictable and complex profiles of sour beers.

However, the craft beer movement that began in the late 20th and early 21st centuries sparked a resurgence of interest in sour beers for several reasons:

  • Exploration of Traditional Styles: Craft brewers and beer enthusiasts have started exploring and reviving traditional beer styles, including sour beers, to diversify the beer market and offer complex, unique flavour experiences.
  • Innovation and Experimentation: The craft beer movement is characterised by its emphasis on creativity and experimentation. Brewers began experimenting with sour beer production, using traditional methods and modern techniques to create new variations.
  • Growing Consumer Interest: Consumers became more interested in diverse and unique flavour profiles, and the demand for sour beers grew. The tart, funky, and complex flavours of sour beers appealed to those looking for something different from the typical sweet, malty, or hoppy beers.

Modern Craft Sour Beers

How are sour beers made - can of the ROS the Spock Sour beer
RPS Brewing – The Spock Sour Beer

This brings us to today, when sour beers are a staple in many craft breweries worldwide. Brewers continuously experiment with ingredients, fermentation methods, and ageing processes to create a wide range of sour beer styles. 

The revival of interest in sour beers has also led to the organisation of sour beer festivals and competitions and a general appreciation for the art and science of brewing sour beers. Hence why I’m writing this article!

Sour Beer Styles: Exploring the Sourness

Sour beers encompass a broad and diverse category of brews with unique characteristics, flavours, and brewing techniques. Let’s take a brief look at the different styles. 


Originating from the Pajottenland region of Belgium near Brussels, Lambics are perhaps the most unique among sour beers due to their spontaneous fermentation. These beers naturally ferment as they are exposed to wild yeasts and bacteria present in the environment. 

This ultimately leads to a complex, sour, and often funky profile. Lambics are typically aged for one to three years before being bottled or blended.

  • Gueuze: A blend of young (1-year-old) and old (2- to 3-year-old) Lambics, Gueuze undergoes a second fermentation in the bottle, resulting in a carbonated, dry, and complex beer with a balance of sourness and earthy notes.
  • Fruit Lambics: These Lambics have had fruit added during the ageing process. The most common fruits used are cherries (Kriek) and raspberries (Framboise), but peaches, blackberries, and others are also used. The fruit adds sweetness, scent, and additional layers of flavour, contrasting with the base Lambic’s sourness.

Flanders Red Ale

Often referred to as the “Burgundy of Belgium,” Flanders Red Ales are known for their deep red colour and a profile that balances sourness, fruitiness, and a malt base. They are aged in oak barrels, contributing to their complex flavours and acidity. These beers are often wine-like, with notes of dark fruits, oak, and a tart finish.

Oud Bruin

Another Belgian sour, Oud Bruin or “Old Brown” beers, share some similarities with Flanders Red Ales but are generally less sour and have a darker, more malty profile. They are also aged in oak barrels, which impart a blend of sour, sweet, and woody flavours. The malt character is more pronounced, with notes of caramel and chocolate alongside the tartness.

Berliner Weisse

A light, refreshing sour beer from Germany, Berliner Weisse is characterised by its low alcohol content and clean sourness. It is traditionally made with a mixture of wheat and barley malts and fermented with yeast and lactobacillus bacteria. Berliner Weisse is often served with a shot of sweet syrup (typically raspberry or woodruff) to balance its tartness.


Gose (pronounced β€œgoes-uh”) is a slightly sour and salty wheat beer from Goslar, Germany. Its unique flavour profile comes from the addition of coriander and salt during brewing and lactobacillus bacteria for fermentation. Gose is known for its lemony tartness, herbal notes, and refreshing finish.

American Wild Ale

While not a traditional European sour style, American Wild Ales have become a significant part of the craft beer movement’s experimentation with sour beers. These beers are typically fermented with wild yeast strains or bacteria (such as Brettanomyces, Lactobacillus, or Pediococcus). They can vary significantly in flavour, from mildly tart to intensely sour. Many American Wild Ales are also aged in wine or spirit barrels, adding complexity.

Innovation and Beyond

The resurgence of interest in sour beers has led to a wide range of innovative brewing techniques and flavour combinations that extend beyond these traditional styles. 

Craft brewers worldwide continue to push the boundaries, creating sour beers with various ingredients, including exotic fruits, spices, and unconventional grains. This experimentation and creativity ensure that the world of sour beers remains vibrant and ever-evolving, offering something new for adventurous beer enthusiasts like us to explore.

Methods for Brewing: How are Sour Beers Made?

Sour beers are crafted using various techniques that encourage the growth of bacteria and yeast, which produce the acids responsible for the beer’s sour taste. Brewers use different methods to achieve this acidity, contributing to their complexity and diversity. Lucky for you, I’m going to break down the various techniques. So strap in – we’re in for a sour ride. 

1. Spontaneous Fermentation

This traditional method involves exposing the wort (the liquid extracted from the mashing process during brewing) to the open air, allowing natural yeast and bacteria present in the environment to ferment the beer. This process is unpredictable and requires a specific environment conducive to the desired microorganisms. Lambics, for example, are produced using this method.

2. Mixed Culture Fermentation

In mixed culture fermentation, brewers intentionally inoculate the wort with a blend of cultured yeast and bacteria, including strains like Lactobacillus, Pediococcus, Brettanomyces, and Saccharomyces. This method offers more control over beer flavour than spontaneous fermentation. The blend and balance of microorganisms can produce various sourness and complex flavours.

3. Kettle Souring

The Kettle Soured Method

Kettle souring is a relatively quick and controlled method to produce sour beers. Before boiling, the wort is inoculated with a lactic acid-producing bacteria, usually Lactobacillus. The wort is then held at a warm temperature for a few days to allow the bacteria to sour the liquid. 

Once the desired level of sourness is reached, the wort is boiled to kill the bacteria, stopping the souring process. The beer is then fermented with traditional brewer’s yeast. This technique is famous for styles like Berliner Weisse and Gose, as it allows for a quick turnaround and a clean, lactic sourness.

4. Barrel Ageing with Microorganisms

As we’ve discussed, barrel ageing involves ageing beer in wooden barrels that previously held wine, spirits, or other beers. These barrels often contain residual microorganisms, including wild yeast and bacteria, which can sour the beer over time. 

Brewers may also directly add specific strains of bacteria or yeast to the barrels to encourage souring. This method is typically used for more complex and subtly sour beers like Flanders Red Ale and Oud Bruin. But just so you know, developing the desired taste can take several months to years.

5. Fruit and Other Additions

Fruit can contribute to beer’s sourness by being added to the fermentation process or as a post-fermentation addition. The natural sugars in fruit can be fermented by wild yeast or bacteria, producing additional acids and enhancing the beer’s sour profile. Other ingredients like herbs, spices, or additional fermentables can also influence the final sourness and flavour complexity.

Factors Affecting Sourness

The degree of sourness and the specific flavour profile in sour beers can be influenced by various factors, including:

  • Type of Microorganisms: Different strains of bacteria and yeast produce different types and amounts of acids, affecting the beer’s sourness and overall flavour profile.
  • Fermentation Temperature and Time: The conditions under which the beer ferments can influence how quickly and completely the microorganisms sour the wort.
  • Ingredients: The malt bill, hop varieties, and any additional ingredients (such as fruit or spices) can all influence the final taste of sour beer.

Brewers can craft various sour beer styles through these methods and factors, each with unique flavours and characteristics, making sour beers diverse and enticing.

Ageing & Blending: Do Sour Beers Get Better with Age?

Whether sour beers improve with age depends on various factors, including the specific style, its initial flavour profile, and how it’s stored. Like wine, some sour beers can develop more complex and nuanced flavours over time, while others might be best enjoyed fresh. Here are critical considerations regarding the ageing of sour beers.

Barrels full of microbrew beer
Barrels Full of the Good Stuff

Styles Suited for Aging

  • Complex Barrel-Aged Sours: Beers like Lambics, Gueuze, Flanders Red Ale, and Oud Bruin, which are already aged to some degree before bottling, can continue to evolve and develop deeper flavours over time. These beers often have a mix of yeast and bacteria that can continue to work slowly, changing the beer’s character.
  • High Alcohol Sours: Sour beers with a higher alcohol content tend to age better because alcohol acts as a preservative. The alcohol can help protect the beer from spoilage and support the development of flavours during ageing.

Factors Influencing Aging

  • Oxidation: While some exposure to oxygen can develop interesting flavours in sour beers, too much oxidation can lead to undesirable flavours, such as excessive mustiness or a damp cardboard taste. Proper sealing and storage are essential to control oxygen exposure.
  • Storage Conditions: Temperature, light, and humidity affect the ageing process. Sour beers, like most beers intended for ageing, should be stored in a cool, dark, and relatively stable environment. Temperature fluctuations can accelerate ageing processes, sometimes in unpredictable and undesirable ways.
  • Bottle Conditioning: Sour beers that are bottle-conditioned with live yeast and bacteria have the potential to change more significantly over time. The microorganisms can continue fermenting any residual sugars and interact with the beer’s other components, leading to a dynamic ageing process.

Potential Changes with Age

  • Flavour Development: Aging can mellow harsh edges, integrate flavours, and allow new notes, such as deeper fruitiness, enhanced sourness, or emerging earthy and funky characteristics.
  • Carbonation: Carbonation levels can change, especially in bottle-conditioned beers. Over time, carbonation might decrease, affecting the beer negatively. No one wants a flat beer!
  • Complexity: Generally, aged sour beers may develop greater complexity, with layered flavours that unfold as the beer warm up and is consumed.

While many sour beers can improve with age, becoming more complex and nuanced, not all will benefit from long-term ageing. 

Sugar Rush: Are Sour Beers Good for You?

Do sour beers have a lot of sugar?
Do sour beers have a lot of sugar?

I know what you’re thinking; surely sour beers are packed with sugar! Despite the common perception, the sourness is not from sugar itself

The initial high sugar content from malted grains is necessary for fermentation, where yeast and sometimes additional bacteria consume the sugar, producing alcohol and carbon dioxide. Of course, the extent of sugar consumption and the resulting residual sugar in the final product can vary widely among sour beers. 

Some sour beers are brewed to be very dry with minimal residual sugar, emphasising the tart and sour flavours, while others might retain or introduce additional sugars to balance sourness with sweetness. The sugar content in these beers is not uniformly high or low. Still, it varies significantly across different sour beer styles and individual brews. 

Overall, I wouldn’t be too worried about drinking a few sour beers and rotting your teeth!

9 of the Best Sour Beers

Surely, that’s enough from me banging on! Let’s have a little look at our top 9 (my lucky number) sour beers!

  1. La Folie 6.5% (New Belgium Brewing, USA) – A pioneering American take on the Flanders Red Ale style, this beer is aged in oak barrels, offering a complex interplay of sourness, oak, and dark fruit flavours.
  2. Monk’s CafΓ© Flemish Sour Ale 5.5% (Brouwerij Van Steenberge, Belgium) – A wonderfully accessible example of the Flemish Sour Ale, known for its balanced sourness, malt sweetness, and fruity notes. It’s a great introduction to the style.
  3. Duchesse De Bourgogne 6.2% (Brouwerij Verhaeghe, Belgium) – A classic Flanders Red Ale that’s rich, complex, and elegantly balances sweet and sour flavours, with notes of dark fruit and a balsamic vinegar-like tang.
  4. Rodenbach Grand Cru 6% (Brouwerij Rodenbach, Belgium) – A quintessential Flanders Red Ale, aged longer in oak vats for deeper flavours. It’s revered for its intricate balance of acidity, fruitiness, and oak.
  5. Fou’ Foune 6% (Brasserie Cantillon, Belgium) – A celebrated Lambic fruit beer aged with apricots, offering a unique combination of tart, sour, and sweet fruit flavours, underpinned by a classic lambic funkiness.
  6. Framboise 2.5% (Brouwerij Lindemans, Belgium) – A rich lambic beer known for its rich, sweet raspberry flavour and character.
  7. Gueuze 100% Lambic 5% (Brasserie Cantillon, Belgium) – A blend of young and aged Lambics, which undergoes a secondary fermentation in the bottle, resulting in a complex, dry, and often sparkling sour beer with a unique blend of funkiness and acidity.
  8. Oude Geuze 6% (Brouwerij 3 Fonteinen, Belgium) – Similar to the Gueuze 100% Lambic, this traditional Belgian style is a blend of aged and young Lambics, offering a refined complexity, effervescence, and a signature sour profile.
  9. Iris 6.5% (Brasserie Cantillon, Belgium) – A unique Lambic made without wheat and with a portion of fresh hops, aged in oak barrels. It’s known for its floral, hoppy character, combined with the traditional sour, funky qualities of Lambic.


Pwoar, this has been a long article, so for those who skimmed to the end, I can’t blame you. Essentially, sour beers have a rich history dating back thousands of years and have grown in popularity thanks to the craft beer movement. Originating from ancient brewing practices, European countries like Belgium and Germany have long cherished their sour beer traditions. The modern craft beer scene has further propelled the interest in these tart brews, leading to a diverse spectrum of sour beers. 

Today, sour beers are celebrated for their unique flavours and complexity, evidenced by various styles from traditional European to innovative American Wild Ales. Let me know your favourite sour beer, or if you’re going to try one for the first time, let me know how it goes! 


Can sour beers be made at home?

Yes, homebrewers can craft their own sour beers with the right equipment and knowledge about the fermentation process. Check out my other article on how to get started brewing at home!

Why are some sour beers fruitier than others?

Many sour beers are brewed with fruits or flavoured during fermentation, which can significantly influence their taste profile. The type of fruit used and the specific yeast and bacteria strains can affect the beer’s final flavour.

How should sour beers be stored and served?

Similar to other types of beer, sour beers should be stored in a cool, dark place. They’re often best enjoyed when served at slightly chilled temperatures, not ice cold, to fully appreciate their complex flavours. Glassware can vary, but wide-mouthed glasses are generally preferred to enhance the aroma and tasting experience.

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