Wild Yeast 101
On March 5th I gave a presentation at the PNWHC about how to catch wild yeast. It went pretty well and I got a friend from my homebrew club to film it for me. So now it’s up on youtube for your viewing pleasure:
I’m also going to write out some words here describing what I talked about in the video for you people who hate watching videos like I do.
What is Wild Yeast
A lot of beers are marketed as wild if they contain brett, brett itself is often called a wild yeast, and WPL644 trois was thought to be brett but is apparently sacc and is being called a ‘wild’ saccharomyces. But if you buy a pure strain of brett from a lab, is it really wild? You know what you’re buying, you know basically how it will behave and what it will do to your beer. Maybe that yeast strain was wild once but I don’t really think that’s wild anymore.
My definition: Wild yeast is yeast that came from the wild
Sources of Wild Yeast
My favorite source of wild yeast is from fruit. As we all know yeast likes sugar and fruit generally is sugary so fruit would be a logical place to expect to find yeast in larger proportions. Some fruits I’ve gotten yeast off of: dates, juniper berries, cherries, grapes, apples. Other good options to try: raspberries, blackberries, blueberries, plums. Farm pressed unpasteurized apple juice is another good source, just get the juice, stick an airlock on it and let it ferment.
If you’re trying to capture a sort of terroir for a specific area then I recommend using fruits harvested from that area, either grown yourself or wild foraged. You can also get yeast off of store bought fruit, just try to get organic if you can and do not use irradiated fruit as that won’t work.
Veggies are another good source, though you’re more likely to find bacteria on vegetables. Think about sauerkraut, you chop up a cabbage, mix in some salt and it ferments itself; plenty of lacto there. Ginger root and it’s cousins (turmeric, galangal) seem to have a plethora of useful microbes hanging out on them including sacc, brett, lacto, even some useful molds.
Flowers are another option for wild yeast, especially if it’s spring and there’s not any local fruit in season to harvest from. I recommend using edible flowers, like apple/plum/cherry/peach blossoms, roses are also edible.
Raw/unpasteurized honey is another good source of wild yeast. Isn’t honey anti-microbial? It kind of is, but the main reason it never goes bad is that same reason that a sack of sugar in your cupboard never goes bad, the high concentration of sugar is the main thing that protects it. the sugar sucks the moisture out of any microbes that happen to be in there, causing them to go dormant or die. But the ones that don’t die are dormant just waiting for the conditions to become favorable, ie the sugar gets watered down.
Insects are another source of wild yeast. I recently read about how Saccharomyces overwinters in the stomach of queen wasps, a few hours later I just happened to find one taking a nap on my smoker, I also had to make starters for a brew that evening so I took it as a sign from God. She went into a starter as well, fermented quite vigorously too. I haven’t used her in a beer yet.
Open air inoculation is probably a method you’ve heard of for producing wild yeast beers. Lambic and other belgian sour beer producers utilize this method most famously and some american breweries have also begun replicating this process. I haven’t done a ton of open air inoculations, from what I’ve read of other people doing it, it’s a good way to catch mold, though I have been successful the one time I’ve tried it.
How to capture
So you’ve got your source, how do you get the yeast that may be on it into a beer? Essentially it boils down to: make a starter, add your source. However there’s a few things to do a bit differently for this starter:
if you’re just trying to capture yeast and not bacteria (yeast in this case includes sacc and brett) you should make a hopped starter, just toss a small amount of pellets in your starter before you boil it, you don’t have to target a specific IBU level hops will inhibit lacto even when dry hopped. Make sure your starter is high enough gravity (~1.030) to end up being above 2% abv when fully fermented out, this will kill enteric bacteria. I also add some nutrient to the starters to give the yeast some extra food. Shake up or otherwise oxygenate the starter before adding your source.
Add the source. If you’re inoculating from open air, I’d pour the starter into a sanitized shallow bowl, cover with cheesecloth to keep bugs out (or don’t) and let it sit out for at least 3-4 hours and not longer than 24 hours, shorter is probably better to minimize oxygen exposure and reduce the chances of catching mold. Then add it back to your starter flask. Put an airlock on the starter and don’t stir or otherwise try to aerate this starter at this point. This is to deter mold and acetic bacteria.
Wait patiently. I’ve had to wait upwards of a week before I noticed any visible activity/fermentation in some starters.
If you want to catch both yeast and bacteria then there are a few things to do differently. Mainly, don’t hop the starter. Add your source and cap the starter with foil and feel free to aerate. Try to keep the starter cool, in the low 60sF if you can, this helps the yeast to have a chance to grow alongside the faster growing bacteria which prefer warmer temps. Again, wait patiently.
Safety Considerations
Some nasty things can potentially grow in this first starter that can make you ill. You’ve probably heard that no human pathogens can grow in beer and this is generally true, but they can grow in wort. The reason why this isn’t an issue for homebrewers is that they are typically pitching a vast amount of yeast into their wort and nothing else is going to have a chance. With this first starter, we’re not pitching a vast amount of yeast, we’re pitching a tiny amount of yeast, and also a tiny amount of other microbes that we may not want.
Here are some things to do to lower the risk of those things taking hold.
Pre-lower the pH of the starter wort to 4.5 or less to inhibit E. coli and C. botulinum. Typical wort pH is 5.0 so you don’t have too far to go to get to 4.5. You can also fortify the wort to 4+% abv by adding a neutral spirit such as vodka, this will inhibit E. coli and outright kill enteric bacteria. You can also keep the starter for a month at room temp (not in the fridge) which will let E. coli really die off. You can read more about safety precautions here. I haven’t done any of these things (partly because I wasn’t aware of them until recently) and I haven’t gotten sick, maybe I’m just lucky? Regardless, if you do happen to be immune compromised then I recommend that you stick with lab yeast.
Did you catch anything good?
So now you’ve got your source in your starter, how do you know if you caught anything good? Well first off, did it ferment? Like I said earlier, be patient, you may have to wait some time to see any signs of fermentation and it’s also possible (but unlikely in my experience) that it may not ever ferment. If it doesn’t ferment then, obviously you didn’t catch anything you’d likely want to put into a beer. If it does ferment, let it ferment out completely.
Did it grow mold? If so you should toss it and start over. Yes there are some molds that aren’t harmful, but I don’t know how to distinguish them from the bad ones so better/safer to just start over.
If it fermented, how does it smell? If it smells awful, like poo or vomit or feet, you probably don’t want that in your beer so chuck it and start over. If it smells good, that’s a good sign that you got something good. If it smells good and didn’t grow mold crash it in the fridge, decant the pseudo beer from the top of the yeast and give that a (small at first) taste. It’s not going to taste exactly like beer but it’ll give you an idea. If it tastes good then you probably got something good.
You probably noticed I said toss it and start over a number of times above, while my success rate for catching wild yeast is above 50% there are many roads to failure at this step so you may want to make up multiple starters at one time to increase your chances of success.
Step it up
Now that you’ve caught something good it’s time to step it up to eventually pitch into a large batch. You can do a starter now how you normally would, though if you’re going for just yeast it won’t hurt to continue using a few hop pellets in your starters. Feel free to aerate your starter like your normally would at this point.
Make beer!
For newly caught yeasts I typically have a standard saison recipe that I like to pitch it into, but you can let your culture choose the style of beer you brew, if it seems very fruity, maybe a british or american style would be more appropriate. Spicy/bretty would lend itself to a saison or farmhouse beer. bubblegum and clove flavors could do well in a wit or abbey style beer. Did you go for bacteria and get some sourness? Brew a Berliner Weisse or Gose. Whatever you choose to brew for this initial large batch of beer, I’d steer away from overly hoppy or malty styles just so that you can really get a good understanding of the sort of flavors your yeast produces.
Keep in mind that your wild yeast may take longer to ferment a beer. I typically give my beers at least two weeks in primary sometimes as long as a month depending how busy/lazy I am. For the first trial of a new yeast, when it seems to be done fermenting ie the beer has reached expected FG (or lower) and doesn’t seem to be dropping any further, I like to rack a gallon into a separate jug, put it under airlock and stash that away for 6+ months just to see if the yeast does anything further with the beer. Sometimes after tasting that aged beer I’ve wished that I had left the entire batch to age. The rest of the beer I’ll keg, I recommend against bottling, especially for this first batch just because you don’t know if they yeast will slowly continue to produce CO2 and result in bottle bombs. If you are unable to keg then you could bottle and store the bottles in the fridge after they have primed, but I still caution against that as I’ve had some jars of slurry carbonate in the fridge. Cold temps aren’t a guarantee of stopping some wild yeasts, they can be very hardy.
Save the slurry
After racking the beer off the trub, I just dump it all into a jar and stick it in the fridge. Put a label on the jar or you will forget what it is. I have 2 mystery jars in my fridge right now. When I want to make a beer with that yeast again, I’ll make up a starter and just take a scoop of the trub from the jar and grow it up in the starter. In this way I always have a sort of baseline from which to draw, every beer with that yeast is ‘second’ generation. How long can you store it? I’ve had one jar in the fridge for three years and still got viable yeast out of it, though it took a lot longer for the starter to get going. Maybe it’s just that particular yeast, but like I said wild yeast is typically hardier than their coddled lab cousins.
Where to go from here?
Well obviously, make amazing beer. If you want to get more scientific you can learn about making plates for isolating specific yeast strains from your culture and making slants for better long term storage. I haven’t done either of these things yet. As we know with homebrewing, the rabbit hole goes ever deeper and you can go as deep as you want.
More resources
Here are some more great resources for info about wild yeast beer, sour and funky and other crazy beer experiments.
You’re probably already familiar with The Mad Fermentationist. If not it’s a great blog about wild and mixed microbe beer making (among other things). he has also written a book called American Sour Beers that I can’t recommend highly enough.
There is a facebook group called Milk the Funk that is just amazing. It’s full of tons of smart people who are happy to share their knowledge and are doing a ton or really interesting things with beer. Joining that group has vastly improved my facebook feed. Milk the Funk also has a website with a great wiki full of tons of great info.
The Yeast book by Chris White and Jamil Zainasheff is also a great resource though it can get pretty technical at times. It is packed full of great info about yeast in general.
Another great resource is Wild Brews by Jeff Sparrow, this book deals more with the production of Lambic and sour Flemish ales. There’s a ton of great info about a lot of the microbes we’re looking to catch though: Saccharomyces, Brettanomyces, Lactobacillus, and Pediococcus.
I hope this info is helpful to you. If you have any questions hit me up on twitter. Go catch some yeast!
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Update: A Spanish homebrewing blogger requested to translate this post into spanish for his readers: here’s the post!
Update: A French homebrew blogger has translated this post into French.
