Over the years my blog posts and videos have reached a surprising number of readers/viewers, especially those on wild yeast. I continued to be amazed that my blog – which started off as nothing more than a brewing log I couldn’t lose – is of interest to so many. (And, by extension, thank you for your interest in this article).
One of the more recent effects of my “fame” (lots of air-quotes around “fame”) is that I am being approached to provide my point of view and “knowledge” to other forums. Not long ago I was asked to write an article on brewing with wild yeasts for the Canadian Homebewers Association – Canada’s equivalent of the AHA. This article takes a deep-dive into how to collect and brew with wild yeasts.
I am re-posting this article below for those who are interested, although I encourage you to check out the original over at the CHA. And while you’re there, if you are a Canadian homebrewer, why not join the CHA and help them in their mission to promote the hobby of homebrewing in the great white north.
Canada is a massive country with an expansive range of habitats. Within our borders are environments ranging from the Great Sandhills desert of Saskatchewan, the dry and frigid arctic, the damp and forested west coast, the towering Rockies, the windswept parries, the rocky Canadian shield, the storm-swept East coast, and of course, the asphalt and concrete expanses of our cities. This diverse landscape is home to an equally diverse collection of wild yeasts – many which have the potential for use in the brewery. The recent explosion in homebrewers and breweries utilizing wild yeasts has created a lot of interest in these yeasts and the beers they make. But many brewers are unsure how to begin, or are concerned about the risks to their equipment or health. In this article I will describe a simple method that can be used by any brewer to begin exploring the yeast in their area, in a manner which is safe, reliable, and which doesn’t require any equipment beyond that commonly used to make yeast starters.
Where to Find Wild Yeast
One of the first questions many people ask me about wild yeasts is where they can be found. The short answer is “everywhere”, but its not quite as simple as that. There are about twelve genera (groups) of yeast which are known to be effective fermenters. And while there are a lot of differences between these yeasts, most of them share a similar lifestyle. These yeasts tend to spend most of their time living off trace sugars found in piles of decaying leaves, or in the guts of insects. What these yeasts are doing is biding their time – waiting for a fruit or berry to fall on their pile of leaves, or for their insect to feed on some damaged fruit. When this happens, the yeasts do something odd – rather than efficiently extracting every bit of energy out of the sugars in the fruit, they instead use an inefficient metabolic pathway to rapidly convert the fruit’s sugars into ethanol. This kills off many of the other bacteria and fungi that the yeast would otherwise have to compete with, and afterwards, the yeasts slowly consume the alcohol. For the brewer this means that while its possible to capture yeast from nearly anywhere, we can target specific locations to improve our chances.
The best places to find wild yeast are inside of insects that feed off of fruits and flowers – bees, fruit flies and the like – or on fruit which has recently fallen from trees. You can also collect yeast from fallen leaves, fruit still on the tree, tree bark, green pine cones, and the leaves and stems of any plant. Wind will also carry yeast, and as such it is possible to collect yeast from the air – indeed, this is where some of the yeasts used in traditional lambic fermentation come from.
Types of Wild Cultures
When collecting wild yeasts, you can setup your collection and purification processes to provide you with different types of cultures. Coolships – the yeast-collecting method used by traditional lambic brewers – collects a range of yeast and bacteria, into a wort conducive to the growth of both. The resulting mixed fermentation contains both alcohol-producing yeast and lactic-acid procuring bacteria, resulting in a beer which over a period of months to years, ferments into a complex and acidic beer. Beers produced in this manner can be wonderful, but the time it takes to produce these styles of beers, the need to blend multiple beers, and the risk of producing an undrinkable beer, makes this a less approachable style for brewers new to wild yeast. The second option is to produce yeast cultures – either of mixed yeast, or of a pure yeast strain. These yeast ferment and behave similar to commercial beer yeasts, and generally will produce a beer in a few weeks. Isolating a pure yeast strain is a complex process, but generating a mixed-yeast culture that is otherwise free of bacteria and moulds is something any homebrewer can do.
Risks & Safety
Before describing how to isolate wild yeast, it is worth spending a moment to discuss the potential risks. The main risk is isolating an unwanted mould or bacteria alongside your yeast. In most cases these will not present a health risk to you – but can be a source of unwanted off-flavours and difficult-to-remove contamination of your equipment. Common beer-spoilage organisms you may isolate include lactic acid producing bacteria, acetic acid producing bacteria, unpleasant smelling enterobacteria, and moulds. And, of course, there is a low but non-zero risk of isolating something pathogenic – some of the enterobacteria can be pathogenic, while some moulds produce toxins that can be hazardous. The good news is that these risks are very low – brewers utilized wild cultures safely for thousands of years prior to the invention of pure yeast cultures in the late 1800’s. The even better news is that it is simple to setup your isolation method to eliminate these risks.
How to Collect & Brew With Wild Yeasts
There is no one correct way to collect wild yeasts, but the method I am outlining here is my preferred method for collecting wild yeasts free of contaminating moulds and bacteria. The principal behind this collection method is straight forward – using commonly available brewing ingredients we create a growth media (modified wort) which will support the strong growth of the yeast we want, while making an environment hostile to the bacteria and moulds we want to avoid. What you will need is:
- Wort at a gravity of 1.045 – 1.065, hopped to at minimum of 10 IBUs (preferably 25 IBUs or more). This can be extra wort from a brewday, or wort prepared from dry malt extract hop pellets.
- Lactic or phosphoric acid
- Cheap vodka, whiskey or white rum, 40% ABV (nothing flavoured or sweetened)
- A flask 500 mL to 1 L in volume, or a mason jar and lid of similar volume
- An airlock and bung that fits the flask. If using a mason jar, drill a hole in the lid that tightly fits the airlock.
- A large pot or pressure canner
To the flask/mason jar add 250 mL (1 cup) of wort and ~0.5 mL (1/8th teaspoon) of the lactic or phosphoric acid. If using a flask, cap the flask with a piece of tin foil and bring to a boil on your stove for 10 minutes. If using a mason jar, cap the jar with a solid lid but leave the sealing ring loose enough for steam to escape. Place the mason jar in the pot and fill the pot with water as deep as possible – typically 1-2 cm above the liquid level in the jar. With the lid on the pot, bring it to a boil and boil for 20 minutes. Alternatively, if you have a pressure canner, place the foil-capped flask or loosely sealed mason jar into the canner, and following the instructions for your canner, can at 15 PSI for 20 minutes. If you prepared the media by boiling, it should be used within a day of preparation. If pressure canned, media in a flask can be stored indefinitely until needed. Mason jars do not reliably seal when partially filled, so they are not suitable for long-term storage, even if pressure-canned.
When you are ready to collect yeast, bring the media to room temperature and add a 1/8th volume of the cheap vodka/whiskey/rum. E.G. if you prepared 250 mL of media, add 35 mL (just shy of 1 standard shot) of the spirit, which will give the media a starting alcohol concentration around 5%.The media is now ready to use – the acid acidified the media below the point where most harmful bacteria can grow, the hops suppress the growth of lactic-acid bacteria, the alcohol will suppress many bacteria and yeast which are not tolerant to higher alcohol levels, and by using an airlock, you will prevent the growth of oxygen-requiring moulds and acetic acid bacteria.
To collect yeast from the air, simply open the jar or flask and leave it for 6 to 12 hours in the location from which you want to capture yeast. To collect yeast from fruit, insects, bark, and other objects, simply drop the object into the flask or jar (cut it down to size if needed). After the period of air exposure, or immediately after adding the object, cap the flask or jar with an airlock, and place it somewhere to ferment at a temperature of 18 – 25C. Depending on the amount of yeast captured and the fermentation temperature, visible signs of fermentation will appear anywhere from 6 hours to 3-4 days later. If activity is not seen after 7 days, assume the capture failed and try again. Do not use the yeast immediately once fermentation activity stops – you want to wait at least one week once fermentation ceases to give the alcohol time to kill any unwanted organisms. At this time smell the starter and inspect it closely – it should smell yeasty and beer-like, it may have fruity, earthy or leathery aromas, and you should see a layer of yeast on the bottom of the flask/jar. It is not uncommon for wild yeasts to settle poorly, and as such your media may be cloudy. The media should not smell foul (vomit, faeces, smelly feet, etc), should not have an unusual colour, and should be free of any mould-like growths (fuzzy or slimy objects). If the media looks and smells right, you’ve successfully captured some wild yeast that are ready for brewing!
How to Brew with Wild Yeast
There are no special steps or procedures needed to brew with wild yeast. Normal sanitation procedures are needed to prevent contamination of your beer, and similarly, normal sanitation procedures are sufficient to eliminate wild yeast from your equipment (i.e. you do not need dedicated equipment). The yeast should be treated like any ale strain – use a starter to build up a proper pitch of yeast, prepare your wort as per usual, and ferment at temperatures between 16C and 22C. For average-gravity ales, wild yeast should complete fermentation in 1-2 weeks, but it may take several additional weeks for the yeast to settle. Gelatin or other fining agents can greatly accelerate beer clarification at this stage.
The yeast themselves are very diverse in their flavour characteristics, so it is best to test them first in a small batch of beer (1 or 2 gallons), using a neutral recipe to allow the yeast characteristics to dominate. I prefer a basic saison base beer for this – 50:50 wheat malt:pilsner malt, 1.050 SG, 25 IBU of a low-alpha hop (Fuggles, Goldings, or a noble hop) and a small 10 min flavour addition (usually a noble variety). Based on the yeasts flavour profile, you can then select appropriate beer styles that will complement the yeast. Wild yeasts are more attenuative than brewer’s yeasts and typically have apparent attenuations of 80-95%. Likewise, most of these yeasts will be POF+, meaning they will produce phenolic flavours similar to those produced by trappist, saison and hefeweizen yeasts. These flavours can vary from mild to intense, and range from earthy/leathery notes through to spicy pepper and clove-like notes. These yeasts often produce a notable ester (fruit) character in addition to the phenolic flavours, with these flavours ranging across bubblegum, pears, fruit-punch, grape and citrus notes. Once you know the flavour profile of your yeast, you can match it to an appropriate style. Fruity but not overly phenolic yeasts often complement traditional US-style hops such as Cascade and Centennial, and work well for a rustic take on an IPA. More phenolic strains tend to work well with Belgian-inspired recipes; the malt and hop bills of saisons, Belgian pale ales and wit beers tend to complement the stronger “funky” character of these yeasts. The phenolic and fruit characters of these yeast also tend to work well with fruits and spices; either in beer, or in other beverages such as wine, cider or mead.
Brewing with wild yeasts offers a unique opportunity to add a local flair to your brewing and is well within the technical capabilities of the average home brewer. The method I’ve outlined in this article is a good starting place for those interested in brewing with wild yeasts, and whether your goal is to sample your local terroir, develop a house yeast strain, or to enter the world of yeast bioprospecting, this method will give you a starting culture of highly fermentative yeast with which you can begin your explorations. And while collecting yeast from your own backyard is the very definition of brewing local, it doesn’t have to stop there. There is a large community of brewers across Canada – and around the world – who share their unique strains in order to explore the diversity of wild yeasts from across the globe.