I volunteered to give a talk on bioprospecting (aka wild yeast capture) to my home brew club, the AABG, before our May monthly meeting. This post is a recap of the material I covered in that talk, supplemented with links to sources I pulled from and/or more information on specific topics if you want to dive further down the rabbit hole.
- What is bioprospecting? Capturing local microbes and assessing their viability for fermenting beer, cider, wine, etc.
- Sources of microbes:
- Open air capture – you can do this like a coolship with a whole batch, or leave jars out covered with cheesecloth. Generally done in cooler weather, especially for coolships which use ambient temps to cool down the wort.
- Fruit and flowers – harvest any time they are available, check for toxicity of the item you’re harvesting!
- Fresh pressed apple juice – usually only available during apple harvest season. If it’s available other times of the year it’s been stabilised either with UV or sulfites and won’t contain viable microbes.
- Mason jars are awesome for bioprospecting in your garden or for carrying out on walks to collect things.
- Two main capture methods:
- Coolship – cooling the whole batch of beer in a shallow vessel overnight (commercial mostly – can build a home scale version if you’re serious). This is time of year dependent, needs to be cool enough overnight to get the wort temperature down. On home brew scale, leaving it out long enough to cool to just above pitching temps is good, overnight probably isn’t needed and can increase the chance of mold.
- Jars of wort – easy! You can make extra wort when brewing or use extract. Can use them as mini coolships and leave out for a few hours in your backyard or add fruit/flowers to the jar directly.
- Probably don’t want to leave small volumes out overnight, though with such small volumes it won’t hurt to try.
- Make sure what you harvest and put in the jars is not toxic!
- Wort modifications can be helpful to keep unwanted growth of bacteria out.
- Hops – either boil or just adding a pellet or two to limit bacterial growth. Hops can provide anti-microbial benefits without isomerising the alpha acids.
- Acidification – pH 4.5 or lower to inhibit enterobacteria and C. botulinum.
- Once you have inoculated, you want to limit oxygen exposure to prevent mold growth (if you’ve ever made kraut – just like that). It’s tempting to open the jar up a lot to smell it and see how it’s doing, but you must resist.
- Watch for active fermentation, keep an eye on pressure build up if not using an airlock. It can take a few days, maybe up to a week, but any longer just try again. You’re safer for longer periods if you’ve acidified the wort.
- Once fermentation has occurred, crash it, and decant the wort. Pitch the cake into a larger starter to see how well it does.
Safety and Contamination
- Wild caught microbes are unknown without scientific analysis, but we can know a few things without a microscope or DNA sequencing:
- Bacteria or Yeast? Behaviour can tell us bacteria vs yeast, such as vigorous fermentation and presence of acid production.
- What is safe?
- First step: smell – if it doesn’t smell foul (fecal, vomit, cheesey), proceed. Mild aromas might be OK, doesn’t hurt to step up and see if it goes away.
- Is there mold? Some are OK with mold early on, I am not. Your choice.
- Measure ABV: 2% or lower? Not safe and a crap fermentor anyway
- Measure pH if possible, but not necessary – can indicate safety and if you have lactic acid bacteria or not.
- Some enterobacteria (e.coli) can survive up to 28 days in fermented beer, be patient, but you can step up the initial capture
- Keep your clean beers safe
- Bioprospecting can lead to capturing many kinds of microbes, separation of some equipment (plastics) isn’t a bad idea, just like making sour beer. Even some yeasts can stick around and cause attenuation and off flavour problems (Brett and Sacc var diastaticus).
What Can You Catch?
Things to Discuss
- What can your microbe(s) metabolise?
- Simple sugars – glucose, fructose – if it can’t do these then it’s basically useless for our purposes
- Maltose – not all wild yeasts can break down maltose, this would be see as poor attenuation
- Lactose – Brett anomalus & some bacteria such as Lactobacillus and Pediococcus.
- Long chains polysaccharides – some yeast and many useful bacteria are capable of breaking down longer polysaccharide chains than your standard brewing yeast. This is usually evident by very low final gravities.
- Pellicles – they are likely to form and can be made by any of the microbe species we can catch. Below are some important notes about pellicles.
- They are considered biofilms (currently) and comprised of many things, such as proteins, long chain sugars, and other material.
- They indicate oxygen ingress into the fermentation vessel
- They don’t mean something is right or wrong with the beer
- They don’t indicated the presence of a specific microbe, it is not currently possible to identify the organism creating a pellicle based on a macroscopic visual assessment.
- “Science” doesn’t know what they do exactly, but protection from oxygen is not the leading theory – there is a lack of evidence to support that theory.
- Disturbing the pellicle isn’t known to have any impact on the beer. The pellicle might reform or it might not.
- They may or may not disappear after they form (referred to as ‘dropping’). A common misconception is that you need to wait until the pellicle drops before the beer can be packaged.
- Milk the Funk Wiki – a resource of incredible depth for all things to do with sour, funky, wild, and weird in brewing.
- Sui Generis Brewing – Introduction to Hunting Wild Yeasts
- The Mad Fermentationist – Ambient-Spontaneous Yeast Starters
- Bootleg Biology – DIYeast: Isolating Yeast
- Sui Generis Brewing – Yeast Wrangling
- Wild Yeast 101 – Mutedog Fermenting