Yeast is an essential part of the production of beer, spirits and wine, but not all yeasts are made equal! Each strain of yeast gives alcohol a unique flavour profile and helps to develop the taste and aroma of a drink. Brettanomyces yeast, more affectionately known as ‘Brett’, is a particularly interesting strain of wild yeast that has been growing in popularity over recent years despite having a historic reputation as a spoilage microbe in the wine industry.
In this article, WSET educator and writer Julia Lambeth looks a little deeper at Brett and its place in wine and beer production.
Of all the potential aromas and flavours that can be found in wine and beer around the world, those ‘funky’ aromas that come from the influence of Brettanomyces yeast - or ‘Brett’ for short - can be some of the most divisive! For some winemakers a subtle influence of Brett adds complexity, while for others even the tiniest amount is unacceptable. For some beers, it is key to their style and something that is highly sought after. Personally, I am a fan of the funk, but know many other wine and beer drinkers who would not go near it. So, what are these funky aromas and how can you know when to expect them?
What is Brett?
‘Brett’ is a type of yeast that is associated with the production of particular aromas:
- 4-ethylphenol (4-EP) – imparts medical, farmyard or barnyard aromas
- 4-ethylguaiacol (4-EG) – imparts spicy or smoky aromas
- Isovaleric acid – sweaty socks
It is easy to see from these descriptions why these aromas could be considered unpleasant and would be unacceptable at high levels, as they could impact the balance of aromas of a wine or beer. But at lower concentrations they can be considered to add complexity or a little ‘funky’ character. So, when we talk about characteristics of Brett, it is really the combination of these aroma compounds that we are talking about, not the actual microbe itself. It should also be noted that individual drinkers will have different sensitivities to these aromas. What one person finds to be overwhelming, another person may not notice to the same extent.
As a microbe it is something that is invisible to the naked eye, but can grow in wineries and breweries, and is often found in oak barrels used for maturation. When it gets in contact with an alcoholic beverage, usually after the initial alcohol fermentation is finished, it will start consuming any leftover sugar and then producing the array of aromas above. Sometimes wine or beer can even be bottled with some Brett, and these aromas will then continue to develop once bottled.
Brett in wine
The presence of Brett aromas in wine is more common in red wines, although it is also possible in white wine too. It is considered by some to be a fault, no matter how subtle the influence is. As it is a type of yeast, it can be found on the grapes, in the winery or in oak barrels, and so is more common in wines that have undergone fermentation with ambient or wild yeast, or through maturation in oak. Therefore, for producers that want to avoid the development of the aromas, strict hygiene protocols have to be followed, minimising opportunities for yeast cells to come into contact with the wine. This can include treatment of barrels, pipes and equipment with steam or sulphur dioxide (SO2), and then making sure microbe populations are measured regularly, and wines are filtered before bottling. However, prevention is better than cure, as once there is an appearance of these aromas in a wine it can be hard to isolate the source and eradicate them. Some wineries will immediately separate and quarantine barrels that have been found to have an influence of Brett. And then there are tales of wineries being partially destroyed and rebuilt just to ensure that no trace of Brett remains! It is also hard to control, so once there is a small population it could easily grow to a large population, so trying to maintain a ‘small’ influence of Brett is considered to be impractical. However, some wineries do try and keep Brett in some barrels but not others, and so will use more stringent hygiene practices around certain barrels, such as making sure that everything that comes into contact with those barrels is sanitised before being used for anything else.
So how do you know if a wine is going to have an influence of Brett? Well actually, that is still quite tricky. It is not going to be indicated on the label (unlike with some beers), nor will it be included in the description of the wine. It is something that is historically more associated with some traditional European styles, as the fruit-forward style of many non-European wines is not considered compatible. But really it comes down to knowing different producers and their philosophy. It will be slightly more likely in minimal intervention styles, and can be one of the components that contributes to the more ‘funky’ styles of ‘natural’ wines. But even then, some natural wines are also designed to be fruit forward. In conclusion, it is not easy to tell!
Brett in beer
There are some beers in which the aromas from Brett are an expected part of the style, such as lambic or gueuze beers from Belgium. These beers are fermented using ambient yeast with the unfermented wort just left open to the air and the various microbes within it. They then generally have long maturation in old oak vessels, and this is where the Brett yeast can really get going. Alongside the influence of Brett there will also be notable acidity from lactic acid bacteria. So, these are beers that do not taste like most other beers you will come across, and again can divide opinion among drinkers! Moreover, if these beers were produced without any influence of Brett that would be problematic, as it is such a key part to the tradition of this style.
Other brewers go for a more subtle influence, and can just allow for some development of aromas in a lager or pale ale style, where it will be balanced against the hop and malt aromas, and is less likely to be noticeably sour. These beers will often have the word ‘Brett’ in the name to signal to consumers that they should expect some funky flavours. For anyone still not sure how to identify the influence of Brett, these beers can be a good way to learn to recognise the aromas that are created, because they are distinct from what you would normally expect in a beer, but present at levels that are detectable.
So, is Brett good or bad?
Well, as with so many things in wine and beer, the answer is: it depends. It will depend firstly on whether or not it is supposed to be there. If a winemaker or brewer does not intend for there to be any influence of Brett it is more likely to be bad. Secondly, it depends on personal preference. If you buy a drink that you are not expecting to have aromas of Brett, which subsequently does have an influence, then that could also be bad if you do not like those aromas. But then, if you are a producer or drinker of gueuze it is a good and expected part of the style – but maybe just give your friends an idea of what to expect before you share a bottle!
About the author
Julia Lambeth DipWSET, Wine Educator
Julia started her career in the wine industry as a novice, working at Majestic Wine for a number of years as a retail manager. After completing the WSET Diploma and winning the Codorníu Scholarship prize, she started a wine tasting company running WSET courses alongside a variety of other wine, beer, spirit and sake events. Julia joined WSET School London's teaching faculty in September 2019 and now teaches our wine courses across all levels.
Further reading and watching
What makes a beer “flavoured”? From natural flavours to added ingredients
Why doesn't wine taste like grapes?
