What Makes Beer Sour?

Whether you love or hate sour and wild beer (we love it), there’s no question it has gained a resurgence in popularity within the craft beer world over the past 20 years. We say ‘resurgence’ because in parts of the world, such as Belgium, these styles of beer have been around for centuries. Also, due to historic brewing conditions it’s likely that all beer, at one point long ago, had sour or wild properties.

But it wasn’t until the craft beer revolution in America that sour and wild ales became a staple of breweries around the globe, with some dedicating themselves strictly to the brewing of those styles. So what makes a sour, sour? And what makes a wild ale, wild? The short answer is yeast and bacteria. The long answer is far more complex, and has had many beer enthusiasts debating as they sip.

The key terms to know on the subject of sour beer are; Lactobacillus (lacto), pediococcsus (pedio), acetobacter, and Brettanomyces (brett).

All these are bacterias except Brettanomyces, which is a yeast, but they all work in a similar fashion, converting sugar to other compounds.


In the case of lacto and pedio both convert sugar to lactic acid – the same acid found in yoghurt – and typically offer a tart lemon quality to beers, often used alone in styles such as Goses and Berliner Weisses, but can be used with other bacterias and yeasts to create more complexity. Acetobacter converts sugars to the vinegar-like acetic acid. Traditionally this can be found in balancing quantities in Flanders Red styles (check out Verhaeghe Duchesse de Bourgogne for a good example of the acetic quality), and we’ve seen it in more aggressive quantities in many modern American sours.


Brettanomyces is a ‘wild yeast’ (you can now purchase it…) ferments sugars the same way the traditional brewers yeasts of Saccharomyces cerevisiae (ale yeast) and Saccharomyces pastorianus (lager yeast) do, but works slower and ferments dryer, than those aforementioned yeasts. Brettanomyces imparts different qualities to the beer you might have heard described as barnyard, horsey, and horse blanket which develop and change over time. It is the key yeast used in Lambic, and other wild ale, production and is found all throughout nature such as on the skin of fruit, in barrels, and in the air.

All of these are friend and foe to beer depending on what you’re trying to brew. If brewing with them you need to clean everything, extremely well afterwards so your next non-sour brew doesn’t end up infected. Very large breweries tend to dedicate an entire section, and sometimes different site all together, to the brewing of beers using these bacterias and yeast so as to stave off any possibility of infection.

Wild Ales

Now, here’s where the debate comes in as to what makes a beer a ‘wild ale’ and what makes it a ‘sour’? Some say ‘wild ales’ can only be spontaneously fermented - when airborne yeasts feed off of natural bacterias often involving the use of a coolship, ‘sours’ are 100% lacto and/or pedio and fermented in tank, and everything else is considered ‘farmhouse’. Others would say that a ‘wild ale’ is anything that utilizes brett whether a coolship is involved or not, and state coolship beers as being ‘spontaneously fermented’, and ‘sour beers’ as using ale and lager yeast with lacto and/or pedio. Meanwhile others would say that all these beers are ‘sour’, but not all these beers are ‘wild’, and we’re sure other others would say something entirely different.

No matter what your school of thought, no matter what they are called, these styles of beers are some of our favorites. So much so that we dedicated an entire club to them! If it’s up to us, we won’t let them become a thing of the past, ever again.

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