Wild Brettanomyces – Fermentation Tests

It’s been a while since I posted on my Wild Brettanomyces project. As a quick synopsis, the natural environment where Brettanomyces lives is unknown. This has made it hard for brewers to find new Brettanomyces, and hard for wine makers to keep it out of their wineries. As a long-time wild/sour beer brewer, I was continually frustrated by my inability to capture and purify wild Brettanomyces from my coolshiped beers and other wild ferments.

Last July I found some scientific papers which identified Brettanomyces as a part of some plant’s rhizospheres (root-associated microbiome). Based on these, in late fall I started a new yeast hunt to see if I could isolate wild Brettanomyces from the rhizosphere of various plants in our vegetable garden. This met with some success, leading to the isolation of two rhizosphere BrettanomycesBrettanomyces nanus and Brettanomyces custersianus. Details on this hunt can be found in the previous posts.

Other Parts in this Series

The Fermentation Tests

I’ll admit that I took a rather lazy route to testing the fermentation characteristics of these two species. Back in November I brewed a batch of my “house” Pilsner. I took 2 liters of this wort and fermented 1L with the B. nanus isolate, and 1 L with the B. custersianus isolate. To look at the effect of co-fermentation, I took an additional 2 L of the unfermented wort and co-pitched the isolates plus my usual lager yeast (W34-70). Everything was allowed to ferment until early march 2023, at which time I force-carbonated the beers and began sampling.

Fermentation Characteristics of Brettanomyces nanus

Yeast clone C1
Brettanomyces nanus

The first isolate was identified as Brettanomyces nanus. This is a relatively rare species which has limited use in commercial brewing. B nanus has undergone some evolution that should allow for good fermentation, including duplication of genes which allow it to process complex carbohydrates. While it did perform well from a fermentation standpoint, its performance in the flavour department left a lot to be desired.

Sole Fermentation: when used alone, this strain attenuated the wort fairly strongly, ending with a final gravity of 1.006 (this recipe typically ends at 1.012). The resulting beer had a strong aroma of burnt plastic and dirt, reminding me of the aroma of a hot car tire. The flavour was just as off-putting – an intense burnt and medicinal flavour that completely overwhelmed any hop or malt flavour.

Mixed Fermentation: somehow, this yeast was even worse in a mixed fermentation. Attenuation was total in this batch (final gravity of 0.998), and it had the same strong aroma – only more intense. The flavour parallelled this. While I’ve never eaten a car tire while it is on fire (or when not on fire, for that matter), I imagine this is what it would taste like. Intense, astringent, and burnt.

Fermentation Characteristics of Brettanomyces custersianus

Brettanomyces custersianus - a wild brettanomyces
Brettanomyces custersianus

The second isolate was identified as Brettanomyces custersianus. This is the red-headed stepchild of the Brettanomyces genus. Unlike all of its other siblings, this species does not ferment complex carbs – it cannot even process maltose or sucrose. When you take into account dextrans and maltotriose (also unfermentable by this species), only around 20% of the sugars in the wort are fementable by this species.

Sole Fermentation: when used alone, this strain barely attenuated the wort, and dropped the specific gravity from 1.052 to 1.047. That is 9% attenuation, and 0.7% ABV. The resulting “beer” was extremely sweet – not surprising given the poor attenuation. Oddly, the beer was also flavourless (other than the sweetness); all hop and malt flavour disappeared. A very disappointing result.

Mixed Fermentation: when used in a mixed fermentation, the resulting beer was indistinguishable from the base beer (e.g. fermented purely with W34/70). Moreover, plating the resulting beer on a medium selective for Brettanomyces produced no colonies, indicating that the B. custersianus had died off completely during the 5-month fermentation.

Wild Brettanomyces – Hindsight and Looking Forward?

I have to admit that while finding some truly wild Brettanomyces was exciting, the fermentation results were a disappointing end to this project. In hindsight, I’m not overly surprised that this yeast hunt met with only modest success:

  1. I started this project far too late in the year. Most of the plants I isolated from were annuals which were either dead, or in the process of dying. Assuming Brettanomyces truly is a rhizosphere organism, it would acquire some nutrients directly from the plants. This food source would be disappearing – or outright gone – in the roots of these dead/dying plants, which in-turn, would lead to lower Brettanomyces levels.
  2. My initial enrichment cultures were poorly planned, and enriched not only for Brettanomyces but also for Debaryomyces and Pichia. This made later isolation of Brettanomyces more difficult, and may have “de-selected” Brettanomyces through competition.

So what comes next?

Given my success in this last-minute and poorly designed project, I’m excited for the upcoming year. I have spent a lot of time researching possible alternative media formulations that may better enrich for Brettanomyces. In fact, I believe I have developed a highly selective media which I am currently testing. I also have a more rigorous sampling plan, and plan to sample at multiple times throughout the growing year. All I need at this point is for the snow to melt, so we can plant the garden!

4 thoughts on “Wild Brettanomyces – Fermentation Tests

  • March 26, 2023 at 1:47 AM

    Thanks a lot Bryan, I understand it makes sense that Saccharomyces are in much more abundance in air than Brett. But there is still something I struggle with : in a coolshiped beer, we should have some Bretts (shouldn’t we??), and even after a while, we should have more than Saccharomyces (as explained in https://suigenerisbrewing.com/index.php/2018/09/22/brewing-wild-jersey-city/). So starting from a coolshipped beer, and waiting something like a year, and with a proper enriching media (complex sugar), I can’t figure out why it would be so difficult (I started the experiment, but will take a while before there are results), so there is probably something I am getting wrong here. Would you be OK to briefly explain how you proceeded in your previous attempts to isolate Bretts from coolshipped beers and why it was so difficult ?

    • March 26, 2023 at 5:56 AM

      Most coolshipped beers are later fermented/aged in barrels, and that’s where the brett appears to come from. Keep in mind that traditionally, sour beer producers would continually reuse barrels, allowing brett to be propagated in that format. Blending and mixing of beers also helps to ensure the spread of brett amoung barrels. Once established, brett is nearly impossible to remove from a barrel.

      Additionally, some breweries do Additional things to help ensure the good Brett’s (& other cultures) make it into their beers. Some put a portion of old beer into each new batch, others spray their walls and rafters with food beer to try and establish a more consistent culture in their brewhouse, etc. But in those cases you’re not capturing the brett from the “wild”, and rather are using a semi-domesticated culture.

      For coolshipped beers that are aged in stainless steel, finding brett is pretty rare unless additional cultures are added. Several North American producers have struggled with this, as they don’t have decade/century old brewhouses fully impregnated with brett, or a large supply of barrels already housing their own brett cultures.

  • March 24, 2023 at 1:55 PM

    Hello Brian. A bit disappointed indeed, but full of promesses for next season !
    Could you elaborate why you think it is so difficult to isolate bretts from coolshiped beers ? It is also something I am looking into. I intended to do an enrichment media with maltodextrins, so that only yeast that can process complex sugars (and hops to exclude bacterias) can survive. Can I have your thoughts on that ?
    Thank you so much 😊

    • March 25, 2023 at 7:13 AM

      I think its simply a matter of abundance. Saccharomyces is pretty common, especially in the guts of the insects that often end up in coolships. Its also common on the bark of some trees, and in leaf litter, meaning that its fairly easy for it to become airbourn (a good breeze is probably enough). Brett is much rarer, and even in vineyards and other places where it’s an issue, is very hard to find. If the assumption that its a rhizosphere organism is correct, this would make sense, as it would typically be closely associated with plant roots. This would keep it below ground (so wind transfer would be unlikely), and it would be sequestered away from the sugar-eating insects which often carry saccharomyces.


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