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Brettanomyces in beer - wild fermentation and the funk brewers came to love

In the world of wine, Brettanomyces is most often a fault, an animal note that most winemakers fear. In beer it is the opposite: for a whole family of styles it is not a flaw but a desirable, even deliberately pitched feature. These wild yeasts give lambics, gueuze, saisons and Flanders reds their unique funk: notes of barnyard, leather, hay, and at the same time tropical fruit and citrus. They stand behind the wild, rustic character no classic strain can give. Brett in beer is a conscious choice, not an accident. Here is a guide to Brettanomyces in beer: what it is, what styles it creates, what flavour it gives, why fermentation with it takes so long and why in beer it is an asset and in wine a fault.

What Brettanomyces is

Brettanomyces, Brett for short, is a genus of wild yeast, different from the classic brewing yeast Saccharomyces, which ferments most beers. Brett works differently: more slowly, more strangely, and produces completely different aromatic compounds. These yeasts are hardy, can work where others cannot, and ferment sugars that ordinary yeast does not touch. In most beer styles Brett is considered a contaminant, giving unwanted off-flavours. But in certain traditional styles, especially Belgian ones, it is valued and deliberately introduced. It is the same duality we know from wine, only with the sign reversed. Understanding that Brett is a wild yeast of its own unusual character is the starting point for all the rest: the styles, the flavour and why in beer it is an asset.

Funk - the wild character of Brett

The characteristic flavour Brett gives beer is described by the word funk, that is a wild, rustic, animal character. Typical notes are hay, barnyard, dusty orchard fruit, leather and wood smoke. These are the same animal, barnyard aromas considered a fault in wine. But in beer the funk is desirable, adding depth, complexity and a wild, unique character. Interestingly, Brett can also give notes that are completely different: fruity, lemony and even tropical, like pineapple, apricot or exotic fruit. This combination of animal funk and bright fruit makes beers with Brett so fascinating and complex. Funk is the essence of what Brett brings to beer: a character that is wild, raw and far from the cleanness of a classic lager or ale.

What styles it creates

Brett is the heart of a whole family of styles. Belgian lambics and gueuze owe it their unique profile, as do wild saisons and farmhouse beers. Brett is also found in Flanders reds and in oud bruin beers. What all these styles share is that the wild, sour or funky character is desirable in them, not treated as a fault. This is why breweries deliberately pitch these beers with Brett, sometimes together with lactic acid bacteria, to reach a complex, wild profile. We cover the whole family of sour and wild beers more in sour beers. Brett is the common denominator of these traditional, craft styles. Without it lambic or gueuze would lose what makes them special: that wild, deep, unique character no clean beer can give.

A table: Brett flavours in beer

Let us gather the characteristic Brett notes in one place:

The table shows that Brett is not one smell but a wide spectrum: from animal funk to bright, tropical fruit. This combination of opposites makes these beers so complex.

Why fermentation takes so long

One of the most important features of Brett is the pace of its work. Brett ferments far more slowly than the classic yeast Saccharomyces, which takes days. Brett needs months, and often even years, to finish its work. This prolonged fermentation, though, is crucial for the flavour: the longer time lets complex aromas develop and the esters and phenols responsible for the funk and fruit form. This is why beers with Brett often mature long in barrels or bottles, changing and deepening over time. Patience is indispensable here. Brett cannot be hurried, and its character develops slowly, over many months. It is a completely different rhythm from the fast, clean fermentation of an ordinary beer. The long time is not a drawback but a condition for these wild, complex flavours to form.

Brett esters and phenols

Where do these characteristic notes come from? Brett, like other yeasts, produces esters and phenols, but of a different profile. Certain esters produced by Brett give fruity and tropical notes, like pineapple, floral or apricot. Phenols, in turn, give spicy and wild, barnyard aromas. This combination of fruity esters and wild phenols creates the characteristic duo of funk and fruit. The prolonged fermentation gives Brett time to produce these compounds fully. It shows that the wild character of Brett beers is not magic but particular yeast chemistry, only different from that of a classic beer. We cover how yeast in general creates esters and phenols more in brewing yeast. Brett is simply a different set of the same mechanisms, giving a completely different, wild effect.

Why an asset in beer and a fault in wine

It is a fascinating contrast. In wine Brett is almost always considered a fault, an animal note drowning out the fruit and terroir. In beer, in the right styles, it is a desirable feature, deliberately introduced for character. Where does this difference come from? Wine usually aims for a clean expression of fruit and place, so a wild, animal note gets in the way. Traditional wild beers, like lambic, are rustic, sour and complex by design, so the Brett funk suits their essence. It is a matter of expectations and style: the same note is a flaw where cleanness matters, and an asset where wildness is valued. It is the best example of how fault and character are often a matter of context. The same microorganism spoils one drink and enriches another.

How to sense it in the beer

The influence of Brett is easiest to sense in a lambic, gueuze or wild saison. Look for notes that go beyond an ordinary beer: hay, barnyard, leather, dusty fruit, and at the same time bright, tropical aromas of pineapple or apricot. If a beer is wild, rustic, complex and far from the cleanness of an ordinary lager, that is a sign of Brett at work. It is worth comparing a wild beer with Brett to an ordinary, clean beer, to feel the gulf these yeasts create. Over time you will start to recognise the characteristic funk and link it to wild fermentation. It is a higher level of beer tasting, at which the wild, animal character stops surprising and becomes a legible sign of particular yeast and style. We cover the whole process more in how beer is made.

The essentials in brief

Let us gather it up. Brettanomyces is a wild yeast that in wine is considered a fault, and in beer, in certain styles, is a desirable asset. It gives a characteristic funk: notes of barnyard, leather, hay, and at the same time fruity and tropical aromas like pineapple or apricot. It creates Belgian lambics, gueuze, wild saisons and Flanders reds. Brett ferments for months, even years, far more slowly than classic yeast, and this prolonged fermentation is crucial for the development of complex aromas. It produces esters and phenols of a wild, fruity-animal profile. The same thing that spoils in wine enriches in beer, because it all depends on the style and expectations. Now you know where the wild character of lambics comes from and why brewers came to love Brett.

Note every beer in GustoNote - the style, the wildness and the funk you sense. Over time you will start to recognise Brett by its characteristic wild aroma and understand more deeply how yeast builds the flavour of beer.