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In the simplest of terms, beer fermentation consists of yeast converting simple sugars into alcohol. There are versions of this process happening all over the world, to all sorts of sugars, by innumerable strains of yeast. What this means for you, is that your local homebrew shop isn't the only place you can get yeast for making your beer.
In this article, I'm going to go through some simple steps that with a bit of luck will get you a local yeast strain of your own to brew with. This topic can and does fill stacks and stacks of books, but we're going to stick with just the basics today.
The equipment you'll need for this project can range from stuff you can find in your kitchen up to a lab that would make the CDC jealous. Just like the rest of the homebrewing hobby, yeast ranching can be a real gear treadmill, but it doesn't have to be.
Things you'll need...
  • A handful of small containers (mason jars work fine)
  • Malt extract for making starter wort
  • Raw lemon juice or acid blend powder
  • Plenty of sanitizer
  • Access to a park or a back yard with plenty of vegetation in a cool time of year
Bonus items that make your life easier:
  • Gelatin
  • Stir plate
  • Petri dishes
Preparing your medium...
To start with, make a small batch of starter wort. If you've not done that before, there are examples and videos galore already out there to explain, but the underlying goal is to boil some 1.040 OG wort made from your malt extract. Add the raw lemon juice to the starter wort to lower the ph balance of your wort. The amount that you should add should be 10% of your original volume.
We're lowering the ph because while the yeast that we're after prefers a slightly acidic environment, mold, and other things we don't want, do poorly in acidic environments. Some of the cool kid brewers might add hops to this starter boil for the same reason, but it's not strictly necessary.
If you have petri dishes or shallow containers for this project, I recommend adding the appropriate amount of gelatin to the solution to make it a semi-solid after cooling in your sanitized containers. In a pinch, this isn't necessary, but it helps.
Cover tightly with sanitized foil and let cool until you're ready for the next step.
Inoculating your medium...
When looking for a location to capture your yeast, it's best to aim for a cool location that is undisturbed by passing animals, ill behaved children, and belligerent drunks.
I've lost several yeast collecting mediums to this guy...

The best place to find wild yeast is in the area of naturally occurring sugars. Knowing this, it's preferable to place your open container nearby trees or plants with fruit. Trees leaking sap are a particularly attractive spot.
In addition to the ph considerations, yeast prefers cool temperatures more than competing mold and other undesirables. This makes fall an ideal time for capturing yeast. Ideally, you should place the container in the late afternoon or evening after the heat of the day is gone.
Leave your container open for several hours or overnight, but not much longer. Recover with sanitized foil and leave undisturbed for at least 48 hours.
Another method is drop wild fruit directly into the starter wort or onto the surface of the dish, as yeast lives on skin of fruit. Juniper berries have worked for a few people I know, and of course grapes are another good source.
Selecting your yeast culture...
If your dish was indeed inoculated, you stand a good chance of seeing a change in the surface of your medium by 48 hours. If you don't see something growing on the surface, or in the case of the non-gelatin route, if you don't notice any change in color, then re-cover your dish and give it another 48 hours.
If after four days, you still have no show, make another attempt at collecting. It's not unusal to see a few swings and a miss.
When you see something growing on the surface of your dish, it's time to make your best effort at selecting the yeast and growing it in another batch of starter wort. The chances are high that you caught not only multiple strains of yeast, but also some mold and bacteria as well.
Mold cultures tend to have a furry or spiky shape to their colonies, while yeast will be whitish in color and have a more slimy appearance. You can see in the picture below an example of multiple organisms growing all on this dish.
This is an example of both yeast and mold growing on a plate. Notice that the off-white yeast is has a shiny slimy look to it, while the mold looks like hairy or spiky puffs.

If you've opted to not use gelatin, and you ignore this step while hoping for the best.
After sanitizing a straightened paper clip or other metal prong, scrape off some of the yeast being careful to avoid anything else on the surface of the dish.
Scrape this new yeast into a fresh container of acidified starter wort and wait for it to grow. If you have a stirplate, this is a great time to use it.
Growing the starter culture...
There is good information out there that suggests it is preferably to step up yeast cultures in small increments rather than putting a very little yeast in a comparatively large amount of starter. For me, this is an unnecessary complication for the first effort. We're trying to keep this simple for now.
Within a day or two, your starter should become cloudy and have a small krausen or foam on the top of the container. Within a day or two more, your yeast will have fermented the starter and have been dropping out of suspension leaving a small yeast cake on the bottom of the starter.
Bonus growth phase with 2nd starter...
Considering that we've been doing our amateurish best to create an environment that favors beer fermenting yeast more than anything else, our yeast at this three to four day mark should have far outstripped the other organisms that take longer to grow.
I like to take a small portion of the flocculated yeast cake and pitch it into one last batch of acidified starter wort that I will grow to pitchable size. I do this because the proportion of yeast cells to those of other organisms is likely to be much more in our favor after the first starter, then at the time of the initial scraping.
This is an example of a yeast cake settling out of suspension. A yeast starter after a few days won't have nearly so large or a cake and the separation won't be as clear, but you get the idea.

You should step up the starter to 1 liter for a five gallon test batch or if you're the sensible type, you can stick to just a pint and do a one gallon test batch.
Testing and Final Thoughts...
It's best to use a simple and fairly neutral for your test recipe. You want the flavor of the yeast to come through without being obscured by the over hopping or an overly complicated grain bill. Stick to something that starts near 1.050 OG and has moderate hop addition.
Over the next few weeks, watch your gravities and see what happens. The results range from complex estery strains, efficient but bland strains, and of course stuff that might taste simply awful.
As you've noticed, this isn't an overly scientific or precise method. Rather than a single yeast strain, you've probably collected a blend of yeasts, but it's a great way to have fun getting a "house strain" of your own.
There is a nearly infinite amount of further information to consider when it comes to this topic. If you'd like to know all there is to know about it, I've heard that a master's degree in microbiology from Johns Hopkins is a great place to start. This little article is just to get you started.
Whether the results are great, good, or bad it's a fun project at any rate. Roll the dice and see what kind of beer your backyard wants to brew.
Excellent article manoaction. Love the picture of the Road Warrior. Ol' Mel is a perfect example of what fame and fortune can do to a person.
One of these days I'm going to have to attempt catching some yeasties.
Thanks for the article! The author seems to make a simple operation sound very complicated. Petri dishes are nice but the average Joe doesn't have them sitting around. Too, it's not always fall and not always optimum time to go leave something under a bunch of trees for a day to collect yeast. Any small dish will do! Gelatin is the only thing you need that you may not already have in the kitchen. If you want to be sure you're dishes & equipment & foil are sterile just use a pressure cooker for a make shift autoclave. You'll get very fine and confident results. Isolating cultures of yeast or bacteria is very easy. Rather than doing all the outdoor collecting just drop some fruit or nuts in a small jar of water for a day or so then a few drops of the liquid poured over the growth media (gelatin) will produce the colonies to choose from.
This is just plain awesome! Thank you for posting this. I can't wait to try it. I've become increasingly more fascinated by my little yeasties lately! I think my wife thinks I'm a nutcase, mad scientist. This will really get her going ;)
@ Randy, I thought the author made a seemingly complicated operation pretty simple. I don't think I would have considered trying to catch my own local strains. Also, not everyone has a pressure cooker lying around, and a Petri dish is a heck of a lot cheaper ;)
Yeah I really like this post. I was eventually going to try this a long time down the road, but now I am just waiting for spring.
It might also be possible to pick up some yeast from different countries by using supermarket fruit, but more than likely you'll just get some nasty crap from the store it was sitting in. Or just maybe some good yeast from the store it was sitting in. Like the article says, "Whether the results are great, good, or bad it's a fun project at any rate" Good luck
A ph of 4.25 to 4.5 is the neighborhood that helps stave off bacterial infections. That's a pretty typical finished beer ph.
you should include that, putting a hop pellet or two into the starter will help fight off most bacteria when collecting wild yeast.
Great, thanks for the article. I've been considering a "wild" yeast capture. Locally grown barley, my homegrown hops, water from my mothers spring and backyard yeast... a true homebrew.
The only problem is that you won't know if the yeast in your culture come from the environment or from the container itself. That is, without autoclaving your collection vessel or starting with a commercially-made sanitized plastic tube, you may be simply growing up yeast from your own brewery that still lingers around after washing your glassware.
The best is to do a control, in which you prepare a dish / tube / whatever you're collecting in, but never open it to the outside environment. If even this vessel grows yeast, you know that you're not "catching" wild yeast, but simply growing up a contaminant from your in-house brewing strains.
It would be great if some more detail can be written about how the gelatin was prepared for the petri dish. I have 5 petri dishes that are about the size of a coffee platter and several locations in mind.
When making gelatin, does anyone have a recommendation for how much gelatin to put into the pot of wort before pouring into petri dishes? Is it supposed to solidify by cooling the petri dish in the fridge before putting it out at specific collection sites?
This is what I am assuming:
1) Boil 1.040 wort
2) Add unflavored gelatin based on liquid volume
3) Cool to room temp-ish then pour into petri dishes
4) Chill in fridge to solidify into gel from liquid
5) Bring back up to room temp and
6) Go collect as per the article instructions
This is too funny, just last night laying in bed I said to SWMBO, the next time we are in the High Desert camping, I want to try an open fermentation. Now I'll just rely on collecting the yeast. I would also like to know about the amount of gelatin.
awesome write up! The blackberries are blooming. I should be able to try this soon. Can't wait!
I just did this today. 3 jars sitting in the back yard hopefully attracting yeasties. Only thing I changed is that I used agar instead of gelatin. Used lactic acid to acidify the wort, guessing at the amount. Fingers crossed.
I know this is a few years late, but I've been out collecting wild yeast. In England (and elsewhere) there is a shrub called the Blackthorn - Prunus spinosa. When the blue-black fruits are ripe in September, they have a 'bloom' on them, like very fine dust: this is wild yeast.
For the techie side, get some rubbing alcohol, and a pressure cooker, some petri dishes and a few tools like paper-clips and glass pipettes. Everything that is going to touch your yeast should at least start out sterile. Work in as sterile conditions as you can, there is loads on the Internet about how to work sterile, read it and learn.
Don't use gelatin, use agar-agar, melt it in hot wort at about 1030 SG, sufficient to get a good 'set' jelly, the packet will tell you how much you will need to set one pint. Fill each petri dish with just enough to to just cover the base 1/8 inch thick. Cover each with lids and place in a pressure cooker along with all your tools. Cook for about 15 minutes at 15lbs pressure.
Fetch your fruit from your local hedgerow (it can be grapes, or in my case blackthorn sloes, or plums). Wash your hands with rubbing alcohol, work in as confined a space as possible, if you have a spirit flame, you can use this to form an up-draft in which to work.
Wipe a sterile paper-clip over the surface of the fruit, then immediately, but carefully, lift a petri dish lid, swipe the collected yeast on the surface of the gel and immediately seal the dish.
Keep warm for 24 - 36 hours when you should begin to see the growth of your collected yeast. You can then 'cut out' a piece of gelatin complete with your cultured yeast and go on to propagate it. Then follow the procedures above for increasing your yeast. To get a working sample for one gallon of beer will take you about two weeks - IF YOU ARE LUCKY. If you need to clean your yeast, then look for 'Acid washing yeast' on t'internet.

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