Team Pombe and the Yeast Olympiad



When I first read the works of Percival Greg in Jamaica and his descriptions of yeast no. 18, I became wildly curious about Schizosaccharomyces Pombe. Pombe is a fission yeast, as opposed to a budding yeast, so they divide differently. All brewers yeasts are budding yeasts and pretty much no beverage uses Pombe yeasts but rum (industrial wineries are exploring Pombe to reduce malic acid because they can metabolize it into alcohol). The name Pombe is Swahili for beer and it was first identified in African millet beers in the late 19th century. It has been explored in conventional beers, but is known to produce off aromas in the context. Not even all rums use Pombe yeasts, but typically those of the grand arôme tradition do (I use that term without nationality because I like the ô). Geneticists have been studying them as a model organism for looking at mutations because of how they divide, so when searching for information, you have to wade through a lot of genetic science.





It was initially thought that high acidity correlated to fuller flavored rums, but that isn’t exactly true, the Jamaicans were sort of wrong and Arroyo straightened it all out. More on that later, because it gets really profound [turns out we can throw many asterisks on this assertion].


If you want to mess with fission yeasts, you need to round a bunch up and have them go through a fermentation Olympiad. This is what Jamaica had done very early on, and their Agricultural Experiment Station would send a new yeast out at the beginning of the season. Later in the season, they would find that it often wasn’t still dominant. Arroyo conducted his own Olympics with some extra wild results, and the French have held their own games for themselves. Arroyo doesn’t say much on the actual methods of discovery, but he does describe his pentathlon better than anybody. [I’m developing the birectifier tool Arroyo used for his Pentathalon and it is for sale, here.]


The big test is the yeast’s ability to produce rum oil, which is the mysterious prized metabolic product and something fission yeasts produce more of than budding yeasts (they may not produce it, itself so much as produce an enzyme that unlocks it). Pombe yeasts have to be found at random (a strategic random), isolated and reproduced in pure culture, then run through feats of strength. After they pass the rum oil tests, they have to go to the fusel oil event. For grand arôme rums, fusel oil has to be minimized during fermentation because fusel oil and rum oil fractions overlap in the still. If you use a fusel oil separator in a continuous still, or a decanting technique in a batch process, prized rum oil will be lost, so unlike other spirits, rum has to be that much more in tune with its yeasts. You can ferment molasses with yeasts, distill it, and not get rum, (but my God will they try to call it rum!) They will also probably try to adulterate it instead of learning more about fermentation. Rum is that much more profound than other spirits.

[I wrote more about adapting the birectifier for testing yeasts here.]



[The first plan here was to look for Pombe yeasts in honey where a great looking research paper claimed to have isolated them with a sound methodology. What we learned is that it was only possible from essentially spoiled honey that was harvested with too high a water content.]

[Two years later, we have disproved the first plan, but learned a startling amount and filled in many supporting ideas. We have a lot better understanding of the current usage of Pombe yeasts. Currently only a few have been isolated.]

My initial plan was to understand Pombe kinetics enough to create dominant cultures in varying mediums like apples, raspberries, foraged blueberries, etc very much like what is rumored to happen at Hampden estates. This would also come with free riding bacterial communities. This plan was dashed because though I could possibly construct a starter one way (pied de cuveé) and build a large footing to optimize aroma and fusel oil production. The rest of the wash would be very different and the community would change significantly. An entire community from a starter would bring an elegant sense of terroir, but it would not be correlated to the most extraordinary of sensory values. Until I learn more, my initial best bet is Arroyo style pure culture fermentation. [Years later we learned a lot more about Hampden’s fruit starter which contained an interesting mystery.]

The majority of the rum industry that found themselves with Pombe yeasts have abandoned the practice and in many cases because it didn’t meet their objectives or technical abilities. For a long time, and for much of the world without any established reputation, rum sold largely on price as a race to the bottom commodity. Being most competitive required continuous stills which need continuous streams of wash to run. Vats require capital expenditure and to feed the hungry stills, a quick fermenting budding yeast could turn around a vat much faster, thus reducing expense. In many scenarios, Pombe yeasts also have less alcohol tolerance than budding yeast which means more energy to separate all the extra water. Arroyo and a few other consultants tell tales of massive distillery wastes due to incomplete fermentations. Pombe yeasts are never singled out as at fault, but these distilleries were never systematically testing the boundaries and limits of their yeast workhorses. Biological control requires chemical control and if you don’t even have that, you just cannot mess with fission yeasts.

We are eventually going to see a fission yeast renaissance. The first step is recognizing their current usage on the market and their usage historically. Did New England rum at Felton & Son’s ever use a fission yeast? They did make very full bodied rums and were using dunder. There is one untapped resource left to possibly find this information (and I’m working on it!). Is Hampden estates using the most noble of grand arôme fission yeast processes? Does Cape Verde end up using a fission yeast? In the previous post, I attributed much of their character to cane juice not being defecated or clarified, but if a cachaça producer could end up with a fission yeast, why couldn’t a grogue maker? Answering that question may be as simple as asking how long their fermentation lasts. [Since this was written quite a lot has been learn about all of these questions, especially Hampden.]



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10 thoughts on “Team Pombe and the Yeast Olympiad

  1. Hi.
    It’s known that there are two strain of yeasts in making of original rum: Schizosaccharomyces pombe and Saccharomyces cerevisiae. Second strain is well available, first is not.
    I want to use first strain. Link in your article leads to strain that (as i understood) needs to be specially raised/grown. So, it can not be used as usial yeast that sells in regular stores.
    I found special yeast made for wine:
    In the description of this yeast stated that strain is Schizosaccharomyces pombe.

    Question: in yeast that i found, is it the same strain, that mentioned in your article?

  2. Hi Ivan,
    The Scottlab yeast is the same type, a pombe, but not exactly a “rhummerie” strain. You may have to isolate a few yourself and kombucha SCOBY’s are a good readily available source, though isolation can be tricky. Propogating the yeast from a slant may be a challenge if you are working on ferments as big as 500 gallons. The 6th edition of the “Alcohol Textbook” is a great reference for practical lessons in propagation. My colleague has just isolated a few Pombe strains and we are about to start fermentation trials.

    One thing to note is that the African strains often described in the literature are different than the Caribbean origin, rum strains. The rum strains avoid the often cited off aromas. I have no idea what you would find in a Kombucha, but it may prove easy enough to explore.

    Best. -Stephen

  3. I have a few questions about this strain.
    Can you write me your email on email that i indicate when sent the comment?

  4. Also, thanks for your answer.

  5. How are the test trials going sjs?

    Interested to know you findings.


  6. Great to hear from you W.

    A lot has happened since that post. I started collaborating with a microbiologist and we were given access to a historic collection of Pombe yeasts associated with rum production. We have learned a ton and the birectifier has proven itself as a great tool to characterize yeasts and understand ferments. We have brought to life the high pH heavy rum ferments of Arroyo as well as the high acid ferments of Jamaica. Besides characterizing yeast, a lot of the work has been framing the two fermentation approaches in numbers as well understanding the differences so we can draw the two approaches together.

    Please check out the recent posts about the latest fermentation trials and if you have any specific questions, don’t hesitate to ask. I’ve got a bunch of recent unpublished work as we pushed the limits and had some failures with the aim of figuring out where the limits were.

    Cheers! -Stephen

  7. Hi Stephen,

    All of your work is fascinating, and although I’m usually enjoying a good technical reading and then simply going back to “normal activities”, I really wanted to leave you a comment. I have the chance to work for a yeast manufacturer and ended up on your website by looking into rum fermentation (also my favorite Spirit!).

    Going through a few of your articles and googling around its technical complexity gives me even more interest in the drink.

    On a more global picture, thinking of how strains have made up their way into alcoholic beverage through adaptation, experimentation, lack of hygiene sometimes, and natural selection to create the taste we now associate with nowadays drinks fascinates me.

    I will be carefully following your future posts and I am happy to connect through email.


  8. Hello,
    Wow, what a great read! Thank you so much for translating this. So you have had access to more Pombe yeasts? I have a ton of questions, but have just discovered your site so I will do some more reading before I bug you with anything.

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