Thursday, 21 March 2013

Introduction to Hunting Wild Yeasts

My interest in brewing has been life-long; I remember helping my grandfather to make schnapps and applejack when I was a little kid.  As soon as I was legally able to (that's all I'll admit to here) I began homebrewing beer.  At the same time I began my undergraduate degree in Cellular, Molecular and Microbial Biology, leading to a early fusion of my education and hobbies. By the age of 20 I had engaged in a series of experiments to evolve brewing strains (discussed extensively in this thread, over at homebrewtalk). At the same time I began brewing sour & wild beers.

I then made the choice (no comment on whether it was a good one or not) to do a PhD, and thus entered a 7 year period where I was constantly moving and never sure where I'd be 6 months into the future (followed by another 4 years of the same whilst post-doc'ing). Over successive moves I lost my library of "custom yeasts", but not the passion and interest in developing my own strains & wild brewing.

This interest was rekindled last year, after I joined the London Homebrewers Build, my local brew club.  Within the first two meetings I had run into a couple of people interested in brewing with wild yeast. These (beer fueled) discussions led to what I think is a unique project  - we aim to capture, purify and characterize a range of local wild yeasts, with the hopes of developing a strain (or two, or three) suitable for brewing.

This is the introductory post in what will be a series cataloguing this process.  Below the fold is an outline of the strategy and some resources we are using.

So where do we begin?  

The answer is, "with those who have done similar things before us".  I say 'similar', because at this point the closest I've seen to what we're aiming to do is people isolating yeasts from commercial wild beers, or working with Brettanomyces.  Below is a list of links to blogs and other resources covering the purification and identification of these yeasts.  This list will likely grow as this project progresses:

Where do you find wild yeast?

EVERYWHERE!!!  Wild yeast can be found throughout the environment.  They are in the air, on the walls of your house, even growing on trees. Of course, the numbers of yeasts in these sites can vary largely. So we want to target sites where yeast tend to be concentrated.  This includes:
  • On fruit.  This is the mother-load; yeasts thrive on the skins of fruits - especially on grapes, berries and tomatoes (i.e. things high in sugar and acid).
  • On trees (fruit or otherwise).  Yeasts love sugar, and tree sap is full of it.
  • In your house.  While the amounts are not as high as in the above examples, there should be enough.
  • Sourdough starters (or flour).  Wheat flour (and other flours) come pre-packed with yeasts and bacteria capable of consuming the starches and sugars made by these grains.  These organisms are often harnessed to make sourdough bread, but given these are the ones living on grains, they also likely represent yeasts similar to those which brewed the first beers ~10,000 years ago.
  • In the 'wild'. Yeasts can be harvested nearly anywhere there is plant growth - be it a forest, a vineyard, a farm, or a city park.
While there are many other options, these should be enough for us to grab the yeast we are looking for.

How do you capture wild yeast?

Capturing is the easiest part.  
  • Yeasts from fruits, grains and flours: Simply place a bit of the fruit/grain/flour in a solution that will support the growth of yeast (i.e. low-gravity beer wort).  In a few days the wort should be bubbling away with active fermentation - of both the yeast and bacterial sort.
  • From the environment: A container of wort, or an agar plate with suitable media, is placed open in the environment, usually at night, and yeast spores allowed to collect in the media. Care must be taken to protect the wort/plates from insects and animals, but this method allows the capture of yeast from nearly any site.

How do you purify strains?

This question will be a topic of several posts, so I won't go into much detail here. Long story short, after capture we'll have fermented wort containing a mixture of yeasts (saccharomyces, brettanomyces, and likely others), as well as various bacteria.  Using a series of selective media (in the form of agar plates) the yeast will be purified from the bacteria, and then the yeast characterized (again, using specialized media) with the hope of identifying saccharomyces (and perhaps some brettanomyces) yeasts.  These will then be isolated as pure strains, tested for critical features (i.e. alcohol tolerance, reasonable fermentation rate).  Finally, test ferments will be conducted with those strains which pass the test, to identify an strains which have favourable characteristics.

More coming soon...

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