Adventures in yeast wrangling

Jo Caird sets out to tame a wild culture

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The smell of malt fills the house as the saucepan of wort bubbles away on the hob. After letting the mixture cool, I transfer most of it to a sterilised mason jar and cover it with muslin secured with a rubber band. The rest of the wort I carefully pour into two test tubes, one containing a few pieces of plum from my local greengrocer, the other containing a swab I’d previously rubbed over the surface of a pear growing on a little tree in my garden. 

The test tubes I tuck away in a warm corner of my office. The mason jar I leave on my patio table, exposed to the sunshine and gentle breeze of this pleasant September afternoon. Twenty-four hours later I bring it in and store it alongside the test tubes. And then I wait. 

I’m no scientist. In the 22 years between biology A-level and the Covid-19 pandemic, my only experience with test tubes was doing shots out of them at various questionable drinking establishments. I’m no home brewer. But I remain undaunted because I am working for a higher cause – I’m going to become the first British contributor to the Local Yeast Project (LYP), an open-source collection of local yeast strains from around the world. 

Stealing fire from the gods

The LYP is the baby of Jeff Mello, chief yeast wrangler at Bootleg Biology, a yeast lab in Nashville, Tennessee that supplies breweries and home brewers all over North America and advises on how to capture and isolate wild yeast. 

Jeff doesn’t have a scientific background either. He was working in Washington DC as a charity fundraiser when he received a home brew kit for Christmas one year and became fascinated by fermentation. “The yeast was this magical substance: you just put it in there and it works,” he marvels. 

Burnt out, he quit his job and turned his attentions to home brewing full-time. Inspired by the Belgian lambic tradition of leaving cooling wort outside to become inoculated with wild yeasts and bacteria, Jeff experimented by placing mason jars of wort around his garden. Most of the jars grew horrible mould but one of them not only began to ferment but smelt pretty good too. With a bit of judicious googling, Jeff made his own agar plates and isolated his very first yeast, naming it Saccharomycetes arlingtonesis after his local neighbourhood of Arlington, Virginia. 

“It made a pretty nice, clean lager sometimes, depending on how I’d fermented it,” he recalls. “I felt like I’d stolen fire from the gods.”

Driven by a desire to share what he’d learnt, Jeff set up Bootleg Biology and in 2014 began selling kits containing everything a homebrewer might need to capture and isolate their own wild cultures. The aim of these Backyard Yeast Wrangling Tool Kits was not only to raise money for the startup phase of the yeast lab, but also to “empower people to take tools of science and demystify them so that they can have the power to control fermentation, nature, yeast, and appreciate things that are local to them, give those things value,” Jeff explains. He also offered a storage service – “because even the most intrepid homebrewer doesn't have a negative 80 degree freezer to store their cultures”. 

It’s with one of Jeff’s kits that I’m attempting my own yeast wrangling experiment, emboldened by his promise that “if you follow the process as it's laid out, it should work fine. It may seem intimidating but if I can do it, then anyone could”.


Fermentation celebration

Two weeks have passed since leaving my wort to ferment in the dark, during which time I’ve created the agar plates I’ll be using to isolate any cultures I find. It was easy to do, and I’m pleased with the results, a neat stack of petri dishes in the door of my fridge. 

I peer into the mason jar, wary of disturbing whatever might be growing there. Except that there’s nothing to disturb; the wort looks exactly the same as it did two weeks ago. I’m no expert, but I can’t see any evidence of fermentation at all. Disappointed but undeterred, I reach for the test tubes and…bingo: whiteish sediment at the bottom of each one. 

I allow myself a moment of celebration – during which I mull over what I might name my yeast, a strain that will surely turn out to be of immense value to not just brewing but possibly humanity as a whole – before setting to work isolating whatever it is I’ve grown. 

Changing the beer world

There are over 500 cultures on Bootleg Biology’s LYP database. The vast majority were captured in the United States, but a handful were sent in from elsewhere in the world, including Costa Rica, Norway and Belgium, by homebrewers, citizen scientists and members of the BB team on their travels. 

The aim of the project, Jeff explains, is to “have a better understanding of wild yeast cultures.” On Jeff’s to do list is a collaboration with university researchers with a view to using techniques such as genome sequencing to really dig into the resource he’s helped to collect. “I want to contribute something to the world,” he says. 

Jeff admits that his ambition of having every US postal code – all 40,000 of them – represented on the database is “not a realistically achievable goal”. But he isn’t letting that worry him: “Starting a yeast company without knowing anything is also not a realistically achievable goal. I have an immense amount of patience, so let's check in in like 30 years,” he says with a laugh. 

There’s plenty to be getting on with in the meantime. “My goal has really been to contribute to people's science knowledge, but also to change the beer world in some way. 

“Helping people as they try to make a new beer or change people's perceptions of cultures, whether they're wild or not, or change our assumptions of how we brew – that to me is what makes it feel good at the end of the day.”

Mark Goodwin of Cellarest Beer Project, a brewery and tap room in Asheville, North Carolina, has a similar ethos. “I wanted to make people rethink what wild is. When people hear ‘wild’ and ‘wood fermentation’ they automatically think of funky, sour beers,” he says. “When I opened they were probably really confused about what I was doing.”

Mark first began brewing with wild-captured yeast when working for Portland-based Cascade Brewing but really got into it as a home brewer in the years leading up to setting up Cellarest in 2020. 


There are over 500 cultures on Bootleg Biology’s LYP database

“I really wanted to try to find ingredients as locally as possible. And yeast is one of those things that people often overlook,” he says. “My goal was to make beer that's super specific to the location.”

Having captured various tasty cultures in his garden – including from wisteria and azalea plants, and a blackberry – but not yet in a position to start brewing professionally, Mark turned to Jeff. “Because I was home brewing, I didn't have a safe place to keep these cultures," Mark says. “I send it to Jeff, he freezes it, keeps it in storage.” Mark then gets the yeast back in a format ready for brewing at a commercial scale. That wisteria-captured yeast, for example, is used as the base for a wide range of Cellarest beers, from IPAs to stouts to saisons. “I was lucky to find that one,” he says. “It’s always a gamble.”

It's alive

Jeff and Mark both make isolating wild yeast cultures sound pretty easy so I’m excited to begin the process of inoculating my home-made agar plates. The most science-y bit so far, it involves sterilising a paperclip (supplied by Jeff, a nod to the “bootstrap” origins of his own journey with yeast wrangling) in a flame, dipping it into liquid containing wild yeast, and dragging it across the agar.

Five days later, I’m thrilled – and slightly disgusted – to find something growing on my plates. Some of it looks like lichen, some looks like snot. None of it, however, can be described as “medium-sized, white to off-white, nicely rounded colonies”, which is what I’m supposed to be looking for to restreak onto a new set of plates (with the aim of eliminating all the other unwanted cultures in the process). I decide to press on regardless in the hope that it’ll all come good in the end. 

It’s a similar picture when I repeat the process six days later, but I’m fascinated to see how the first set of plates are getting on by this stage: while the original mason jar culture is a collection of evil looking green and orange splodges, and the pear culture looks like a slug has crawled across the agar, the plum culture actually – sort of – looks like it’s supposed to. Taking this as a win, I swab a likely looking colony from the most recent plate of plum culture, dunk it in some wort then send it off to Bootleg Biology. Now all I have to do is wait for an email from Jeff lauding my scientific rigour and confirming that my culture – Saccharomycetes hackneyesis, I’m going to call it – is a gift to the world of brewing.

Terroir and taste

The immediate focus of the LYP is finding unique microbes for use in brewing, but this area of Jeff’s work has a wider application too. “The number one question that I'm asked is, ‘Can you tell me if a certain geographic area has a certain character?” In other words, Jeff explains, “Is terroir real?”

In viticulture, the idea of local conditions – soil, climate, terrain - imparting particular characteristics on a wine is widely acknowledged. That hasn’t really been the case with craft beer, however, a product that involves several different ingredients that, hitherto, are likely to have been sourced from very different places. But as interest in hyper-local production grows, with brewers looking to the lambic tradition for inspiration, the issue of terroir in beer has become a live one. 


Russell Sykes, who deals with a wide range of wild yeasts in his role as lead brewer at the Wild Beer Co. in Somerset, is unequivocal on the subject. 

“With the wild ferment, you're capturing a sense of place, a sense of terroir through the yeast,” he says.

He gives the example of Somerset Wild, a now discontinued Wild Beer Co. beer that was brewed with yeast captured from an orchard close to the brewery. “It tastes like cider,” he says. “There are no apples in it and there are no hops; all the flavour is coming from the yeast. Part of that flavour is not only from apple trees but from our local area as well.”

Russell’s hunt for interesting local yeasts continues, isolating the cultures found in local honey and even wasps, following recent research that shows evidence of wild yeast overwintering and crossbreeding in the insects’ guts.

Mark Goodwin of Cellarest, on the other hand, isn’t so sure about terroir in beer. For him, working with locally captured wild yeast is a “really fun aspect of brewing beer. But I don't know if it's adding a tonne of noticeable flavour.”

Jeff is still on the fence about the potential of local yeast for terroir too – but he’s hoping that the LYP might one day provide some answers. In the meantime, he believes that local wild cultures can be a powerful tool for brewers looking to tell a story through their beer.

“Finding wild yeast isn't actually that difficult. I recommend finding something that has a good story that reinforces their mission or their focus,” he explains. 

“Yeast doesn't have a face, it doesn't have a name. It's our job to do those things for it, to give it a story. The better we are at that, the more it seems approachable and appealing to people.”

My own yeast story has no happy ending, alas. I email Jeff a few weeks after posting my sample to check how the analysis is going and he tells me that it never arrived. I’m not going to lie - I’m pretty disappointed by this news. After all the trouble I went to, for the culture to have just got lost in the post is a blow. 

But then I think back to what Jeff said about his wider aim for Bootleg Biology as a means of broadening access to science: I may not have captured and isolated a unique local yeast strain, but the joy of rediscovering my scientific side feels like an end in itself. My place in the brewing hall of fame can wait. 

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