Sometimes, amid the kettle souring, NEIPA, and kveik crazes, it's hard to remember what got me into this yeast thing in the first place. For me, many of these roads trace back to finding a beer called Orval as a cash-strapped and beer-curious undergrad (it's super cheap!) and falling in love with the mysterious, musty-apple character of the beer. Later, I found out that was a result of yeast called Brettanomyces bruxellensis, and once I was trusted to wield an inoculation loop in a microbiology lab, I isolated my first Brett strain - from a bottle of Orval. I'm fortunate to still get to work with that Brett, and many others. As I close up shop after inoculating a new round of Brett propagations, I'm reminded that there is still so much to discuss when it comes to our funky friend.
Recently, I co-authored a paper on Brett primary fermentation*, alongside a team of researchers at the University of Guelph. This research started quite a while ago - 2015, in fact. The long time span from start to finish should hint at one critical quality of Brett: it doesn't like being studied. This is not a normal yeast. One Brett strain can perform perfectly in one trial, then totally crap out in another. Many of the rules we play by in the Saccharomyces world seem to not matter to Brett. This makes for challenging research. But in the end, we got a cool study comparing different Brett strains which helped form the basis for our understanding of 100% Brettanomyces ferments at Escarpment Labs.
The lead author of the project, Caroline Tyrawa, went on to complete her Master's on Brett beer research, where she investigated the intricacies of Sacc-Brett copitches, and looked into the nutritional needs of our funky friend. We are hoping that the University team will be able to polish up and share some of their newer Brett findings for public consumption soon.
*This paper is behind a paywall, please contact us if you would like to access a copy.
Brettanomyces is used in a wide range of beers to produce its signature funky and fruity aromas. The funk mostly comes from volatile phenol compounds, like 4-ethylguaiacol (wood smoke, bacon) and 4-ethylphenol (band-aid, barnyard). The fruitiness comes from esters, especially the "fatty acid esters" ethyl caproate, ethyl caprylate, and ethy decanoate, which offer up a host of pineapple and orchard fruit aromas.
The reason that Brett is so totally different from conventional Saccharomyces yeast is that it is a very different yeast, which has evolved quite differently. The two species diverged evolutionarily around 200 million years ago. For context, 200 million years ago, Pangea was still a thing. What's cool here is that Brettanomyces and Saccharomyces have both figured out how to adapt very well to man-made fermentation niches. Adapted and genetically distinct populations of both species seem to be common in beer and wine. However Brett has adapted to beer and wine in different ways than Saccharomyces, resulting in a yeast that is much slower fermenting and worse at handling anaerobic (oxygen-free) conditions, but much better at surviving in low nutrient environments, and able to scavenge a broad range of food sources. Brett is kind of the cockroach of the brewing world.
Brett is about as evolutionarily far apart from Saccharomyces as roundworms are to humans! Figure from: Shen, X.-X., Opulente, D. A., Kominek, J., Zhou, X., Steenwyk, J. L., Buh, K. V., et al. (2018). Tempo and Mode of Genome Evolution in the Budding Yeast Subphylum. Cell 0, 1–13. doi:10.1016/J.CELL.2018.10.023.
What kinds of Brett are out there?
When we talk about Brett in beer, we mostly talk about two species: Brettanomyces bruxellensis and Brettanomyces anomalus. There are other species that pop up here and there, but these two species represent the vast majority of Bretts found in lambic and other traditional Brett beers. However, since fungal genetics are messy, there have been some remnants of the past that have stuck around in our Brett language. For example, "Brettanomyces lambicus" was once considered a different species, but genetics revealed it to be a group of Brettanomyces bruxellensis. Likewise for "Brettanomyces clausenii", which is really Brettanomyces anomalus.
In general, Brettanomyces bruxellensis is a more aggressive species, with strains far more likely to be able to ferment wort sugars and often able to produce intense amounts of volatile aroma compounds. Brettanomyces anomalus is comparatively tame, with most species unable to ferment complex malt sugars, but often with interesting enzyme activity that can help to biotransform fruit and hop aromas.
We should think of Brettanomyces bruxellensis like we think about Saccharomyces cerevisiae - a species of yeast with huge diversity in characteristics, and that if you were to use 200 different strains, each one would produce slightly different results from all the others. So even within that one species, there are a huge number of tools at our disposal to influence flavour of Brett beers.
The family tree of 1,488 Brett isolates, showing the different families according to the fermentation environment. Figure from: Avramova, M., Cibrario, A., Peltier, E., Coton, M., Coton, E., Schacherer, J., et al. (2018). Brettanomyces bruxellensis population survey reveals a diploid-triploid complex structured according to substrate of isolation and geographical distribution. Sci. Rep. 8, 4136.
Modern research on Brett Beers
Brettanomyces has been used (whether intentional or not) in the production of some of the most complex and fabled beers of the world: lambic, Berliner Weisse (the real stuff), Flanders Red, and so on. In the modern craft beer world, Brett has also been employed in different ways. Brewers eventually started to even explore Brett in a pure culture ferment ("Brett primary", "100% Brett" and so on). They discovered that Brett primary ferments can yield different results compared to when it is used in secondary fermentation or copitches. The results were often described as fruitier or more intense.
The bulk of the work on Brett primary fermentation was done by Chad Yakobson of Crooked Stave. He investigated the impact of strain selection, pitch rate, and lactic acid on the fermentation and flavour production of pure Brett ferments, significantly pushing forward our knowledge of what can be done with Brett in beer.
Our research published in the Journal of the Institute of Brewing sought to extend this work by also exploring temperature. We also noticed that the fermentations in Yakobson's work were quite slow and in some cases incomplete, and so we wanted to screen a range of our own Brett strains to see how they stacked up and to determine which might be suitable for primary fermentation. We also wanted to see how wine and beer strains compared to each other in the wort.
This is the critical challenge of Brett primary fermentation: it's slow. Even with an ideal strain under ideal conditions, the fermentations took at least three weeks.
Brett primary fermentation is slow! While some strains started fermentation reasonably fast, the fermentation rate toward the tail end of fermentation can be quite slow with Brett. Also, note that many strains did not complete primary fermentation in the allotted time.
What did we find in our study?
We found that there was a pretty big difference in fermentation efficiency between Brett strains and that only a few were active at a lower temperature (15 ºC) in the 28-day experiment. We observed that Brett, when fermented at the higher temperature, was fruitier for some but not all strains. The phenols were generally fairly consistent between temperatures and strains, with some small differences.
This suggests that a colder or pressurized Brett secondary fermentation could yield funkier flavours, not by enhancing funk but rather by suppressing esters.
When the flavour profiles were analyzed with PCA (a statistical method to assess multidimensional data in a visually simplified manner), we saw a stronger shift in flavour profile in response to temperature for the beer strains versus the wine strains. In general, the wine strains were more neutral in flavour, which presented opportunities for us in product development. For example, we have used wine strains of Brettanomyces bruxellensis in our Ontario Farmhouse Ale Blend, where we are using the Brett to "tame" the banana esters of the primary wild Sacc strain, without being too overly Brett-estery.
We also did some growth assays, finding that there were differences in the Brett growth on sole carbon sources, especially cellobiose (a wood sugar).
Fruity esters like ethyl caproate (pineapple) were enhanced at a higher temperature and in the beer-origin Bretts (the wine strains are PEST III and PEST IV). Meanwhile, funky phenols like 4-ethylguaiacol (wood smoke, barnyard) were relatively consistent between temperatures.
Practical tips for Brett primary fermentation
Secondary fermentation with Brett is relatively simple: add some Brett in secondary, and let the flavour develop. However, we get lots of questions about Brett primary fermentation, and most of the troubleshooting we encounter with Brett is related to Brett primary fermentation. So we want to make sure that you can have success with all Brett ferments, and don't write off this fantastic yeast.
1. Brett primaries tend to have a long lag phase. This can be reduced somewhat by "feeding" the culture prior to use. Our typical suggestion is to take the homebrew or pro pitch and feed it with the same volume of fresh wort, and grow with air bubbling or a stir plate until activity is observed, then pitch into your fermentor. This will help get the yeast fermenting, and help create more biomass so that the culture can focus on fermentation rather than cell growth.
2. Pitch it fresh. We aim to produce Brett primary pitches as fresh as possible for pro clients so that this is achievable. For homebrew packs, we strongly encourage a starter.
3. Oxygen is central to controlling Brett growth and fermentation. Brett needs oxygen for growth and fermentation, and is not able to switch to fully anaerobic fermentation as well as Saccharomyces. While too much oxygen can encourage Brett to produce acetic acid, lots of oxygen is ideal in pitched wort, and can even be applied sparingly during the lag phase to encourage Brett growth. Since Brett is very good at scavenging oxygen, it will generally reduce dissolved oxygen fairly well.
4. Some strains work better than others. In this study, our Brett D, Brett Q and Brussels Brett were used (but they are under different names in the study). These three performed primary fermentation reasonably well. Others, such as the BBY026 and BBY028 strain are used in our Saison blends for Brett character in secondary fermentation.
5. Consider blending in a pinch of Saccharomyces. While not a Brett primary ferment, it is possible to pitch a low level of Saccharomyces into a Brett ferment at the start, or after the Brett has had a few days to start fermentation. Since even a small amount of Sacc will ferment a beer faster than Brett, this can help with turnaround times. We've had good results even blending our clean Cali Ale with Brett D. Saccharomyces produces more glycerol and nutrients than Brett, which may even help Brett with growth and fermentation in a copitch environment.