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On a snowy Tuesday night in February, 17 sourdough enthusiasts crowded into the kitchen classroom of Calgary’s Cookbook Co. to learn secrets from one of the city’s best-known bakers.

Attendees passed around a bucket of sour-smelling, bubbling goo, each taking a whiff of its clean, briny scent as Aviv Fried contemplated where the community of bacteria and yeast in each sourdough starter (a mixture of flour and water that eventually gets inoculated with wild yeasts) originate. They could come from the air, as bakers in San Francisco believe, or the surface of the grains ground into flour (which Fried believes is most likely), or even from the bakers’ hands.

Fried is a scientist by training; he earned his master’s degree in biomedical engineering, but strayed from his intended career path to teach himself how to bake and ultimately opened Sidewalk Citizen Bakery which he runs with his partner, Michal Lavi. As with other modern artisan loaves, their chestnut-crusted sourdough is made using a naturally fermented starter – the same method all bakers used to coax their dough to rise before Fleischmann’s created the world’s first shelf-stable, fast-acting, commercially manufactured yeast in the late 1860s. The development streamlined the bread-baking process at home and enabled mass production.

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But wild yeast exists everywhere – it thrives on the surface of our skin, plants and fruits, anywhere there’s a source of carbohydrates to feed on – and many bakers such as Fried have returned to old methods of harvesting the naturally occurring life forms to create their loaves, giving the bread a more complex flavour and texture. Sourdough diehards have been known to take their open jars of starter for a walk to encourage them to diversify by mingling with a wider community of wild yeasts. (Some are so dedicated to the craft that they bring their starters on holiday in order to keep them on their regimented flour and water feeding schedules.) Meanwhile, stories of 100-year old sourdough starters kept alive for generations are like trophies earned for dedication to the art of baking. For these enthusiasts, what it all comes down to is a desire for a more meaningful connection with the source of their food.

Fried’s sourdough class was fully prepared to adhere to strict feeding schedules for their newly fermenting starters, slurries of precisely measured flour and water left to colonize by attracting yeast or letting those pre-existing in the flour do their thing on their countertops, although Fried admits you can neglect your sourdough starter in the back of the fridge for a full year, forget to feed it and still be able to coax it back to life. There’s something renegade about wrangling wild yeasts you can’t even see, cultivating the microbes yourself to do your bidding.

The process doesn’t just fascinate bakers: The single-cell fungi are also key ingredients in beer, wine, cheese and some fermented products such as kombucha. Many brewmasters and winemakers also prefer to coax the invisible micro-organisms from their natural surroundings into a vessel of mashed grains or strained grapes; more diversity in the strains translates to a more complex flavour profile, one that reflects the terroir.

“Yeast has an incredible personality – people don’t realize the flavour components it contributes,” says engineer-turned-brewmaster Graham Sherman, who along with his team at Tool Shed Brewery made their first batch of spontaneously fermented beer by loading a batch of barley wort, the liquid extracted after the mashing and steeping of grains, into the back of his pickup truck and touring it around the province.

The goal was to produce a terroir beer, an authentically Alberta brew made entirely with locally grown and malted barley and hops – as well as yeast. It’s a method that has been used for centuries by brewers in Belgium, who place a shallow stainless-steel pan called a coolship filled with wort up in the rafters of their breweries to trap wild yeasts. Many home brewers in Belgium and other European countries have family strains they’ve cultivated over the years, much like the generations-old sourdough starters.

Sherman worked with the brewmasters program at Olds College near Calgary to isolate individual strains of yeast, discovering 15 that were potentially usable. “Some were absolutely horrific,” he says of the beer they brewed using those strains, “but three were fantastic – a sort of wild Belgian saison-style – and one strain was previously unidentified.”

They sent the winning strain to Escarpment Labs in Ontario, where founders Angus Ross and Richard Preiss – both of whom have graduate degrees in molecular biology from the University of Guelph – have amassed more than 900 unique cultures in their yeast archives. It took Tool Shed three years to ferment, isolate and then come up with a recipe for the brew they called Alberta Pride. The beer sold out in weeks, but the strain will remain at Escarpment Labs and be available to anyone who wants to try it, boosting biodiversity in an industry where 90 per cent of beer on the market is produced using a small handful of strains from two families of industrial domesticated yeast.

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“Starting from scratch, you’re definitely subject to a lot of variability,” says Preiss, who with Ross has built a business foraging for interesting cultures. Because harvesting wild yeast is kind of a gamble, isolating usable strains prevents unintentional fermentation by rogue yeasts, which in the business is considered contamination – much of the reason so many in the industry will tell you brewing beer is 90 per cent cleaning tanks.

Preiss says in many beer styles, yeast is a big flavour driver. “They take what’s there and do all sorts of things metabolically; some yeasts can convert more or less of the sugar, making a sweeter or drier beer, and some of them take compounds in the malt and hops and transform them into citrusy or floral flavours. Hops and malts are a little more tangible – you can see them, handle them, taste and smell them, but you don’t necessarily want to taste and smell yeast. But it really has a huge impact on the flavour profile.”

In Oliver, B.C., the Culmina Family Estate Winery’s No 002 Wild Ferment Gruener Veltliner is made using only yeasts from the vineyard in order to develop flavours that are not only more complex, but also unique and indigenous to their vineyard – that add to the wine’s sense of place. Wild yeasts from the grape leaves go directly from vineyard to Petri dish, are given nutrients to propagate and then used to ferment the wine, which develops savoury notes of rising bread and spice with aromas of ripe yellow plum and delicate white flowers.

Other brews aren’t quite as delicate. In Lacombe, Alta., shelves on Steve Schultz’s classroom at Lacombe Composite High School are lined with mason jars; in some, a rubbery SCOBY (an acronym for symbiotic culture of bacteria and yeast), a squidgy mass that resembles a cross between an oyster and a pancake, provides residence for the bacteria and naturally occurring yeast that transform sweet tea into fizzy kombucha.

“We store the SCOBY in a jar we call the SCOBY hotel, and it naturally reproduces every week,” Schultz says. “It’s a great discussion starter with students. And we can sell the offspring SCOBYs or use them in different recipes and experiments.” Schultz has his students make their own batches of kombucha, which take about a week to ferment. They hold several kombucha-making workshops a year and some students sell the fermented drink – which gets its mild effervescence from the yeast consuming sugars and creating carbon dioxide – at parent-teacher interviews, farmers markets and special events.

For home bakers, the process is far less scientific, more mysterious and only slightly less time-consuming. In Calgary, Fried holds two sourdough classes a month and they always sell out; not only are aspiring yeast hunters eager to learn, they’re completely willing to devote the time it takes to produce a three-day loaf and adhere to a strict starter-feeding schedule not entirely unlike having a newborn.

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“I like the idea of having something elemental and primitive living on my windowsill that I keep alive,” says Rick Thomas, an attendee of one of Fried’s sourdough classes who regularly bakes sourdough at home. “It’s like tending a garden of microorganisms that keep mutating and developing flavour, that brings life to something as simple as a loaf of bread. They’ve become a part of our lives – in breads, pizzas, pancakes, anything. I keep them alive and in turn they nurture my family.”

“You get to know your starter,” says Fried, who has never named his, but has staff who have added name tags to their jars in the bakery fridge. “You know when it’s happy, you know when it’s hungry, you know when it’s tired. This is my tool – I need to make it do whatever I want it to do.”

Feed it well and that crusty jar in the back of your fridge will feed you back.

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