- Tom Green
- August 18, 2020
Most homebrewers rely on commercial yeast strains to ferment their beer. As a healthy fermentation is one of the most important aspects of brewing, it’s always a safe and predictable decision to use store bought yeast. But what if you could find great tasting wild yeast right in your own backyard?
Capturing wild yeast is becoming a popular activity for homebrewers. Unique strains of yeast and bacteria local to your environment can produce great results. Placing wort outdoors overnight, near trees and flowers, allows airborne natural yeast to inoculate the wort. From there, the wild yeast is grown and scaled up and used for crafting a unique, hyper-local beer.
Follow our guide to get started wrangling wild yeast. We’ll outline an easy and safe way to collect tasty and viable native yeast.
What is “wild yeast”?Yeast has been used by brewers, bakers, and winemakers for thousands of years. It’s believed that the use of fermentation to make alcoholic beverages dates back as far as 7000–6600 BCE. These fermentations were caused by wild yeast.
Saccharomyces cerevisiae that lived on plants and insects spontaneously fermented the first beers. The reusing of fermentation vessels helped naturally select stronger yeasts. This allowed brewers a high level of control and predictability over their product.
After centuries of research by brewers and scientists – notably Louis Pasteur – yeast was discovered to be a living organism. With a deeper understanding of the function of brewer’s yeast, strains were isolated and commercialized.
Although hundreds of yeast strains have been found for brewing, there are still countless more strains in the world that can make great beer. Living on fruit, trees, and blowing through the air, wild yeast is everywhere.
Lambic breweries famously ferment wholly with wild yeast. In traditional Belgium brewing, fresh wort is inoculated in large open vessels, called coolships. There, lambic brewers rely on wild yeast and bacteria in the environment to spontaneously ferment their beer.
Inspired by these traditional sour beers, modern craft breweries have been brewing more and more with local wild yeasts.
Why should I capture my own native wild yeast?With such a diverse range of yeast offered in homebrew shops, you might wonder why anyone would capture their own yeast. Well, like everything in brewing – because you can! It’s fun, exciting, and makes a great story – but not only that, you can forage unique and delicious local strains.
Terroir – a term normally reserved for wine makers – is the component of a brewery’s product that is unique or native to the region it’s from. There’s no better way to incorporate terroir into brewing than to ferment with native yeast, local to the brewery.
What do I need to capture wild yeast?There are few ways to capture wild yeast. We’ll guide you through how to harvest airborne yeast, as this is our preferred method. It’s a great entry into the wild world of yeast capturing. By using our straightforward process, you should be able to find unique and great tasting wild yeasts in your own backyard.
EquipmentTo get started on your quest to capture local wild yeasts, you’ll need the following pieces of equipment:
- 1L wide mouth mason jar
- Fine mesh cheesecloth
- Elastic band
- Mason jar lid with hole drilled for airlock
- Airlock
- pH meter or testing strips
- Sanitizer
IngredientsA low gravity wort is used to collect the natural yeast. For that, you’ll need the following:
- 1.25 qt filtered water
- 100g of Dried Malt Extract (DME)
- 1g of hops
- Lactic acid
How to capture wild yeastOnce you’ve got your equipment and ingredients ready to go, it’s time to start foraging for yeast. On your quest to capture local yeast, make sure to follow all safety and hygiene precautions. Mold growth is a real threat. Don’t risk consuming anything moldy. It’s best to count your losses and try again.
It may take a few attempts, but eventually you’ll strike yeast gold!
Step 1: PlanningBefore venturing outside and setting up the yeast capturing equipment, there are a few things to consider. Weather, temperature, time of day, and season are all important variables for finding wild yeast.
The best time to find wild yeast is in the evening, when the temperature cools. Ambient temperatures should ideally be around 50F. Spring and fall are great seasons for capturing yeast, but it’s certainly possible with warmer temperatures as well. However, temperatures near freezing are not ideal.
Every regional climate and airborne microflora is unique. Feel free to experiment with ambient temperatures and seasonality.
Once you’ve penciled in the night you want to wrangle some yeast, you’re ready to gather your equipment and ingredients.
Step 2: Preparing your equipment and starter wortPrepare your starter wort by boiling 100g of DME, 1.25 qt of water, and 1 or 2 grams of hops for 20 minutes. The hops are used to limit the growth of wild lactobacillus bacteria.
Adjust the pH of the wort to 4.5 with lactic acid. Lowering the pH helps prevent bacterial spoilage and gives the wild yeast a better chance at growing.
Sanitize your jar and cheesecloth. Dump the starter wort into the jar and cover the opening with cheesecloth, securing it with an elastic band. Leave about 1-2” of headspace in the jar.
For the best results, consider making multiple starters. By placing jars in several places, you have a better chance of picking up a successful yeast.
Step 3: Setting the trapTake your filled jar and place it outside where you want to capture the wild yeast. You want to find a spot near plants, trees, or a beehive. Ensure there is good airflow – you want to give airborne yeasts a good chance of landing on your wort. Keep the jar away from possible pests, like wildlife, as well as any sources of bacterial contamination, like a drain or a sewer.
Leave the jar outside for the night, at least 9 or 10 hours. When you return in the morning, inspect the wort to make sure that no bugs have entered through the cheesecloth. If everything looks good, bring the jar inside.
Replace the cheesecloth with the lid and airlock to seal off oxygen. Allow the wort to ferment, at around 68F, for 1 to 2 weeks.
Step 4: Growth phaseIf all went well, you picked up some healthy wild yeasts. You should start to see signs of fermentation after a few days. Don’t expect vigorous fermentation like in a typical yeast starter. The wild yeast you’ve captured needs time to grow and build. You might see some airlock activity, a small krausen, and the wort may turn cloudy. All normal and good signs.
As fermentation continues, and the pH of the wort drops, harmful bacteria will have a hard time surviving. However, if mold or large solids begin to grow beneath the surface of the wort, discard the starter and try again. It’s likely unwanted and out of control bacterial growth.
Step 5: AnalysisWhen signs of fermentation have ended, it’s time to test the wort. The first test is visual. The liquid should look like fermented beer. Many wild yeasts and brettanomyces produce a pellicle, so this is normal if one still persists. Any mold at this point is a bad sign and the starter should be discarded.
The next test is to smell. The starter should smell clean, lemony, or fruity. Any smells of vomit, feces, or anything nasty is indicative of harmful or bad tasting bacterial growth. This should be discarded.
If the starter smells good, you should check the pH. As long as the pH is lower than where it started (4.5), you’re safe to continue. If the pH has risen, discard the starter.
At this point, it is safe to taste the starter. Pull a small sample from below the surface and taste. If it tastes mild, fruity, or lemony, you should be good to go. Any bad flavor is not a good sign. Also, if the starter beer has dropped clear, that’s a great sign of a healthy fermentation.
Step 6: Stepping upYou’ve now captured and grown your very own wild yeast and are almost at the point where you can use it to make a full batch of beer.
The next step is to make a starter with your new yeast. Follow our guide on how to make a starter to grow your wild yeast into a pitchable size. For this starter, again lower the pH to 4.5 using lactic acid. This is just another step to protect against the growth of any remaining unwanted bacteria.
Once the starter has fermented out, it is now time to brew your first batch of native and wild beer. We recommend starting with a 1 gallon batch. Give that batch 3 or 4 weeks to fully ferment. If the beer tastes good, with no nasty off-flavors, your yeast capturing was a success.
Save the full yeast cake from your 1 gallon batch in a sanitized jar. This is your first native yeast slurry that you can step up and use whenever you feel like brewing a beer with your own terroir.
Final ThoughtsFermentation will always have an aspect of mystery and magic. As fully understood as the science behind it is, it’s still nearly impossible to predict flavor outcomes and yeast expression in beer. Finding wild yeast, possibly never before used in beer, feels magical, while producing delicious results.
Capturing wild yeast will get you closer to finding the ultimate local beer. Homebrewers generally have the DIY ethos. Why not take it to the next level by finding, harvesting, and growing your own yeast.
Frequently Asked QuestionsWhat can I brew with my wild yeast?Determining what stain of yeast you have captured is difficult for homebrewers. Unless you have a microscope and microbiology training, you’ll have to rely on your senses.
Once you’ve grown up a starter, carefully smell and taste it. Imagine what beer style it could work with. If it has a clove or pepper character, consider trying a saison or Belgian style beer. If it’s estery and banana-like, a German wheat beer could do the trick.
Fermenting at different temperatures will also have a large impact on the outcome of the flavor profile. Try a warmer temperature to boost the fruity side, or colder for a cleaner fermentation. Take notes on your results. Experimentation is key when working with your wild yeast. You’ll surely find a tasty recipe that showcases the yeast profile perfectly.
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