Friday, 26 September 2014

Announcing a New Yeast Bank! & A successful Yeast Hunt

As readers of my bank know, I have an interest in wild brews and purifying wild yeasts. I have gone through a series of wild yeast collection attempts, and finally have some success to report (more on that below the fold). In addition, over the past few years I've acquired wild yeasts harvested by other brewers - including the infamous/famous Brettanomyces strains from DCYeast.

I'm splitting off the wild yeasts from my yeast bank of commercial (e.g. Wyeast/White labs/bottle cultured) yeasts. I realize this is a somewhat artificial division, as within the commercial yeasts are yeasts that breweries harvested from the wild, but regardless, I figured this was the best division. The new bank of yeast is still rather small, but it should grow quickly as I purify strains from some successful wild brews I have recently conducted (again, more below the fold). For those of you who like my yeast-culturing videos, you'll be happy to know that I'm using this year's wild-yeast hunt to prepare a video covering the process of isolating pure strains of wild-yeast from beginning-to-end, so watch out for that - it should be up soon.

My "vision" for the wild yeast bank is akin to that of Bootleg Biology, namely a terroir-style project, but in my case the goal is to gather these largely from Canada (although I'm happy to bank wild yeasts from any terroir).

2014 Yeast Hunt (#1)

The Garden of Yeasti-ness
A few months ago I began a wild yeast hunt, which unlike my first hunt, used more likely sources for good wild yeast  - namely, various vegetables and fruits from my wife's amazing garden.

From the garden I harvested a number of things that were likely to contain yeast - raspberries, tomatoes, clover flowers (in the nectar), choke-cherries, blueberries, and more on a whim, a hop flower. A local brewer was also kind enough to provide me with some wild grapes picked from along a river in town, which I then crushed and let ferment much like a traditional wine.

All of these showed very rapid starts to the ferment, but within a week or two it became apparent that I had made a critical error in all but the wild-grape tube - I left the yeast sources in the tubes, along with the wort, and severe mould infestations took hold in all tubes where the yeast sources floated to the top of the tube. In an attempt to rectify this I carefully recovered a bit of the yeast-cake from the bottom of each tube and sub-cultured that into fresh 1.040 wort. Sadly, this did not work, meaning that the two yeast sources which started off mould-free (the raspberry and tomato) remained mould free, while the others turned into an unusable mess.

L->R: Tomato, Raspberry & Grape
This isn't the end of the world - I still have three cultures which are good (grape, raspberry and tomato; picture to the left), from which I should be able to harvest some wild yeasts and other bugs for future brewing projects.

But how do they taste and how well did they ferment? Just as a heads-up, the non-grape yeasts were fermented in a 1.040 unhopped test wort prepared from DME.

Tomato: This mixed culture attenuated highly, reducing a 1.040 wort to 1.004, or 90% apparent attenuation. Despite that high drop in gravity, there was a balancing ester character (apples, pears) that made the wort seem not at all dry. In addition there was the feeling of some body, which I suspect means something in here is producing some glycerol. Surprisingly, there was no phenolic character or acidity; even though there was a thin wax-like pellicle similar to that produced by many souring organisms. This yeast flocks like nothing else; leaving a crystal-clear beer after a vigorous fermentation.

Raspberry: The raspberry was not as attenuative as the tomato - with the test wort dropping from 1.040 to 1.007 (83% apparent attenuation). The finish here is amazingly mild - no phenolic or sour character, and only a minimal ester character. Body was medium, finish had a slight malt sweetness to it. This yeast isn't WY1056/WLP001/US-04 clean, but I think you'd have trouble determining it was a wild yeast if compared amongst some English -style yeasts. This yeast flocculates reasonably well, although it doesn't clear as well as the tomato.

Grape: This yeast was allowed to work on the grape must produced by crushing the grapes the yeast were on. Due to the small amount of liquid recovered I was unable to get a gravity reading, but a post-ferment refractometer reading is consistent with what you'd expect for a finished wine (1.001 or less, depending on what you predict as the starting gravity). The flavour is much of what you'd expect of a commercial yeast used in a red wine must after a few months - lots of suspended yeast give a yeasty flavour, otherwise the wine is bright, tart, flavourful and dry. There is a nice body, again suggestive that something in there is making glycerol. Obviously, it is hard to tell which characters are from the yeast and which are from the grapes, but regardless, it is clear that this yeast can turn a grape must into what appears to be the beginning of a nice wine. Whether or not this yeast will be good for beer, cider or mead remains unclear, but the potential is certainly there.


  1. This is timely, as I've just been exchanging e-mails with a new yeast rancher recently about this sort of thing. Did you take any sort of precautions about cross-contamination when adding the fruit? I'd like to try culturing yeast from oak bark from here in DC, but so far I haven't been able to come up with a way to safely extract the bark in a sterile manner and not damage the tree (not trying to get the DC Arborist on my case) and walking around with sterile knives.

    I'm trying to avoid another DCY01 where I never know where it came from. It's phenolic and intiially produced some brainy-wiry colonies (like this: but never produced much sulfur, which makes me slightly skeptical. Do you think I might be misinterpreting the stuff I've read that says wild Saccharomyces will almost necessarily have the H2S production and POF (although I know '01 is POF+) genes intact?

    1. I didn't take any huge effort to prevent cross-contamination, but I did collect in a way meant to minimize the risk of stuff on my hands getting into the beer. In short:

      1) I collected everything into sterile, 50ml conical tubes
      2) To collect each item I placed the tube underneath the fruit/flower, then cut the stem with a clean pair of scissors
      3) I did this while I was cooling some wort for a wheat beer; I then ran cooled beer straight out of the brew-kettle into each tube
      4) The tubes were then loosely capped and placed in a warm place in a different place in my home than where beer normally ferments

      As for the bark, my approach would be similar to what I did above - using a clean probe to wedge off pieces of bark that I would then catch in sterile tubes. You could then cap the tubes to keep things clean until you could add wort.

      As for H2S production in wild Saccharomyces, I'm not certain. I've yet to have a good pure strain of wild Sacc to test, but in my experience, none of my wild ferments have ever had much of a sulphur character. H2S is highly volatile, so unless you're testing your wort at just the right time you may miss its presence (and likewise, the levels of its production are highly dependent on fermentation conditions).

      I was expecting POF production, but I'm not certain that indicates there is no Saccharomyces in the cultures (in fact, there almost certainty is, given the fermentation rates I'm seeing). But again, POF production is dependent on fermentation conditions - especially the presence of phenolic acids. These usually come from grain, but since I used DME I have no idea what levels of the precursors there was. We as brewers can control the level of these acids somewhat, by minimizing tannin extraction, meaning that we may minimize POF production by wild strains through good brewing practices.