Monday, 5 August 2013

Results: First Wild Yeast Hunt

Thirteen mini-ferments on the go!
A few weeks ago I brewed a Blonde ale.  This batch was slightly oversized, in order to give me enough wort to do a series of mini ferments in beer bottles, using a selection of the yeasts isolated in my first wild yeast hunt.  The goal was simple - to brew a light beer that would let the yeast characteristics dominate, while at the same time producing a beer that would act as both a flavour control, and as a lawnmower beer to get me through the beginning of August.

This is going to be a fairly extensive post, so here is the brief summary.  As per usual, the meat is below the fold:

I selected about half of the 25 strains of yeast I isolated as part of my first wild yeast hunt, and grew up 1ml mini-starters, using 1.040 wort (no hops) and a shaker set at 32C.  These 'starters' were then stored in a fridge for a few days until I could brew the Droit du seigneur Blonde; a low-hop (17IBU), modest-gravity (1.044) ale.  I  brewed an extra 5L of this beer, in order to give enough volume to setup 13 100ml mini-ferments, which were inoculated with the mini-starters.  A month later I ran a flavour testing series, to see what these wild yeasts had produced.  A month may seem like a long time, but since wild yeasts can sometimes be slow, a month gives a long enough ferment for even the slowest of yeasts to ferment to completion.

I did not get any particularly stellar yeasts out of this - about half were oxidative yeasts and barely reduced the gravity of the beer.  I was more successful than I had expected - finding four strains with potential.  But what really came out of this project is a  usable method.  SWMBO'd has a garden full of veggies right now all of them covered in local wild yeast!

All the nitty gritty below the fold.

Picking Strains:

Starters, ready to pitch.
While I ended up with 25 strains of yeast, I didn't test all of them - both because the strains from the earlier days are unlikely to be fermentative (indeed, no drop in gravity was observed until after day 10), and because many of the strains appeared to be similar in terms of their colony and micrograph morphology.  As such, I tried to pick a series of samples which were representative of the yeasts from each sample day, with an emphasis on yeasts from the later days as these later-arising yeasts are the most likely to be of interest.  As such, I took one each of the small mucoid, medium powdery, and large mucoid from day 4, colonies #1 & #3 from both day 10 and day 20, and all six strains from day 30.

Yeasts are temporarily named by date, colony type (day 4 only) and their isolation number.  I.E. D04SM-1 = day 4, small mucoid, colony #1.  D10-3 is day 10, colony 3.  I'll give real names to anything good.

Tasting Notes:

For each strain I am noting the bottle appearance,appearance in the sample glass, aroma, taste, final gravity (FG) of the wort, apparent attenuation (Ap. Atten.), and notes on anything else of interest.  All samples - including the 'control' glass of Droit du seigneur Blonde (fermented with the very neutral US-05) are being drunk warm (room temperature) and uncarbonated.  This brings out the taste of the sample - which, as you'll soon see - is not always a good thing!

Interesting yeasts are highlighted in yellow, otherwise "notable" ones are highlighted in blue.

ID #
Ap. Atten.
US-05 NA (Kegged) Clear, straw  coloured. Mild, fruity esters Neutral, modest bitterness. 1.010
Control Beer, fermented with US-05.  A nice, refreshing beer
D04SM1 Cotton-ball like yeast cake Modest hazy Bread-yeast like Very fruity  sweet 1.036 18%
D04MP1 Floating pellicle Hazy, some yeast chunks Cider Dry, bland 1.005 89% High attenuation, but bland and boring - stale tasting
D04LM1 Chunky throughout brew Snot-like consistency Fungal None -- -- Thick like snot, couldn't measure FG.  No taste (and yes, I tasted it)
D10-1 Thick yeast cake Cloudy Solvent-like, sweet Sweet & lactic 1.037 16%
D10-3 Clear, easily disturbed yeast cake Mild cloudiness Bread yeast and cider Ale-like, estery 1.022 50% May work as a co-fermenter; not ideal for solo ferments
D20-1 Fluffy yeast-cake Highly cloudy Unpleasant, fungal sour/estery 1.036 18% Minimal ferment, surprisingly not bad taste.
D20-3 Lumpy but firm yeast cake Mild cloudiness Minimal, yeasty Sweet, otherwise mild 1.037 16%
D30-1 Compact cake Mild cloudiness Fruity esters Dry, astringent, bitter 1.002 95% Highly attenuation, but unpleasant.  May work as a co-fermenter with ageing.
D30-2 Cloudy Highly cloudy Mild & neutral Sweet, neutral 1.038 14%
D30-3 Cotton-ball yeast cake Heavy cloudy Slight acetone note Sweet, neutral 1.035 20%
D30-4T Thin cake Cloudy Yeast & medicinal (phenolic) Mouldy/mousy 1.036 18% Tastes like Bret, but was minimally fermentative.
D30-5T Cotton-ball yeast cake Mild cloudiness Mouldy Sickingly sweet, horrendous flavour notes 1.040 9% Nasty, flavour outside of what I can find words for.
D30-6T Cake on bottom, heavy ring around top Mild cloudiness, oily surface Yeast  & cider Dry, estey, band-aid like phenols 1.005 89% Possibly Brett, may work well with long ageing

Final Notes:

Out of the 13 strains that were tested, 1 was unpalatable the point of being nauseating, 1 turned the beer into snot, 7 were poor fermenters or otherwise boring, 2 may be usable in mixed fermentations, and 2 may work as a solo fermenters - assuming their more unpleasant characters fade with age.  As success rates go, I think that's pretty good.  Given the results I will continue tests with four strains, including attempting a DNA-sequencing based identification.  Without further ado, let me introduce the strains worth further exploration:

Potential Fermentative Strains:
These are strains which are sufficiently attenuating to be used as the sole organisms in a brew.
  • D30-6T: Medicinal phenolics, esters and highly attenuating.  Ma be Brettanomyces
  • D30-1: Lots of fruity esters, attenuates strongly but produces an astringent finish.
Potential Mixed Fermentation Strains
These are strains with interesting taste profiles, but which lack the attenuation to be used as the sole strain in a fermentation.
  • D10-3: Ale-like esters, but minimal attenuation. May work as a co-fermenter, but its hard to conceive of a place where it could be used in place of a real ale yeast.
  • D20-1: Produces a ferment with fruity esters and a bit of a lactic twinge.  Surprisingly enjoyable, but has an unpleasant aroma.  Weak attenuation means this strain needs to be used in a mixed ferment


  1. Interesting results from your hunt. Keep up the good work.

  2. Very cool stuff. You're brave, tasting some of those!