What brought the director of a Belgian sourdough library to the Yukon? Century-old sourdough starters and a community whose history is singularly tied to an ancient form of bread-making.

For much of the 19th century, Skagway, Alaska, was home of the Stampeders, fortune seekers who made the long journey through the Chilkoot Pass, over the Coast Mountains, and northward to Dawson City in Canada’s Yukon Territory—the capital of the Klondike Gold Rush. Each of the Stampeders would carry on their journey a significant load of goods, the bulk of it consisting of flour. Not much could survive the extreme cold of the arctic north, but bread could. The stampeders would always have something to eat as long as they kept flour and a live sourdough culture close, maintaining it, like a marsupial, at the temperature of his body to keep the microorganisms alive. Sourdough flapjacks were such a large part of the stampeders diet that even today, a person who has lived more than 30 years in the Yukon Territory is known locally as a Sourdough.

This history is what brought Belgian baker, Karl De Smedt, halfway around the world to collect what he describes as one of the rarest “specimens” of sourdough that he’s found yet, so he can add it to the library of sourdough starters he maintains in the village of Sankt Vith, about 87 miles southeast of Brussels. The walls of De Smedt’s sleek library, founded by the Belgian bakery supply company Puratos, are not lined with books, but with refrigerated cabinets, their brightly lit interiors kept at a frigid 35.6° F. Their shelves are filled with glass jars of sourdough strains harvested from places as far-flung as Mexico, Japan, Brazil, Malta, Australia, and France.

The Puratos Sourdough Library in Belgium.

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The Puratos Sourdough Library, which is a part of the Center for Bread Flavour, was created in 2013 to catalog the various traditions of bread-making by preserving the sourdough cultures that make them unique. The starter’s flavor evolves as it ages, making it a unique ingredient that lives and breathes. If a starter is not fed and carefully managed, or in some cases not passed down from generation to generation, it will eventually become dormant or die. “Our idea is to have a space to maintain all the diversity of the most different types of sourdoughs used in the world,” De Smedt told me in April when I visited the library.

The library also keeps back stocks of the original flours used by the “owner” of each starter, which are used to feed the bacterial cultures. Since bacteria and yeast are highly linked to the flour, it is imperative that the starter is fed with the same variety in order to maintain its unique characteristics. European starters still dominate the library’s collection, imported from countries such as Greece, Hungary, Germany, France, and Portugal. Currently, the library houses 16 starters from the U.S.

Italy alone has contributed 37 samples, in part due to the library’s close collaboration with a team of scientists from the University of Bari in southern Italy, led by microbiologist Marco Gobbetti. As De Smedt collects samples from around the world, he sends them off to Gobbetti’s lab for analysis. Together, they’ve cataloged more than 700 different types of ferments and more than 1,500 types of microorganisms, including one lactic acid bacteria called Lactobacillus sanfranciscensis, a lactobacillus named after San Francisco. In Professor Gobbetti’s labs, they’ve identified L. sanfranciscensis in sourdough strains sent by the French baker Eric Kayser from his Parisian bakeries. These microorganisms have spread in ways scientists are still trying to map.

Over the past few years, De Smedt has collected more than 100 sourdough strains from around the world.

The origins of sourdough bread are unclear, but bread has been an essential part of the human migration story for millennia: a simple, hearty product that’s easy to replicate in any climate with the simplest of ingredients. Each of the sourdough starters that De Smedt collects is a complex microbiological ecosystem that begins to grow as soon as the flour is mixed with water. The enzyme amylase immediately begins to break down the flour’s starches into sugars that, in turn, feed the bacteria and yeasts found in both the flour and the surrounding air. The carbon dioxide produced in the fermentation gets caught in the stretchy strands of gluten, which makes the bread rise. The sourdough starter, which usually prefers warmer temperatures, is kept alive through regular feedings (additions) of fresh flour.

The unique flavor, smell, and texture of every sourdough loaf is the direct result of the microbes found in the starter, which in turn depend substantially on the flour (wheat, rye, manioc, etc). “That’s where the beauty of sourdough is: no matter how similar they are, each starter is unique,” De Smedt says.

One such starter brought De Smedt to the northern Canadian city of Whitehorse in Yukon and the home of 84-year-old Ione Christensen. De Smedt heard about Christensen’s starter, which dates back to when her great-grandfather hiked over the Chilkoot Pass from Alaska on his way to Dawson City searching for gold, through an interview she did with CBC Radio. Christensen’s signature dish is waffles, made with the sourdough starter that her family has kept alive since 1897. “I personally have been using it since 1958 when I left home and set up my own kitchen. My mother had it, so did my grandmother and great-grandfather who first came to the Yukon,” she said.

The small container that holds Christensen’s starter has an old and worn label that reads, “100 year old Yukon Sourdough—DO NOT THROW OUT.” De Smedt says it’s difficult to find sourdough starters that have remained alive and within the same family for so long. As a starter is passed from generation to generation, it becomes a part of that family’s history and memories that the sourdough librarian is trying to preserve along with the cultures.

When De Smedt left Whitehorse, he drove 330 miles northwest to Dawson City, subsisting for the length of the five-day journey on pancakes, focaccia, and makla (a Moroccan bread), all made from Christensen’s starter. De Smedt also baked during his journey with a starter passed down from the 1890s that he got from Arianna Sikorski, another home baker he met during his trip. “We made pancakes on an open fire, baked bread on a miners stove and even tried to find gold in the river,” De Smedt says. In Dawson City, he met historian Susannah Dowds, from the Klondike Gold Rush National Historical Park, whose studies focus on historical frontier cooking methods.

Dowds, who wrote her master’s thesis on sourdough and western expansionism at University of Alaska Fairbanks, says sourdough has always been closely associated with major historical migrations like the Oregon Trail (1840s-1860s) and the California and Klondike Gold Rushes, which took place in the first half the 1850s, and the last years of the 1890s, respectively. In all of these difficult journeys, sourdough was both a source of life and a powerful symbol of the frontier spirit. In the primitive kitchens of the frigid far north, keeping a starter alive was as much a mark of accomplishment as it was a survival skill.

“We see something interesting as settlers moved from the more settled East Coast to the West. When settlers moved to remote areas they did not have access to brewers or to commercially produced yeast (widely available by the 1880s), but they would have flour and water: the ingredients for sourdough,” Dowds says.

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The strains are numbered and stored in glass jars inside refrigerated cabinets.

Sourdoughs took pride in their common identity based on shared experiences on the frontier, and the Sourdough identity became a proud inheritance to pass on to future generations.

“As a means of processing a raw foodstuff, a sourdough fermentation is a wonder of nature and culture,” writes Michael Pollan in his book Cooked: A Natural History of Transformation. Humans have been leavening bread for the last 6,000 years, he says, describing the process as “an indigenous technology for improving the flavor, digestibility, and nutritional value of grass.” In her book The Story of Corn, Betty Fussell writes about Native American communities that made a variety of flatbreads with ground, fermented corn. Sourdough as we know it, then, had precedents on the American continent long before the arrival European colonizers.

Wheat arrived in the Americas with European immigration and with it came any number of methods for raising dough with origins in different regional culinary cultures. The first British colonizers came from a culture that, since the 14th century, had favored beer balm—a yeasty byproduct of brewing ale—for leavening. “In Colonial America, brewing and baking were considered to be related skills,” says Dowds. “Cookbooks in the 1700 and 1800s would talk about ‘Hop Rising’ or ‘Ale yeast.’”

On his way back to Belgium from the Yukon, De Smedt stopped in Seattle to meet Will Lawrence-Grant who uses a 120-year-old sourdough starter to make pizza dough at his pizzeria, That’s A Some Pizza. That dough had taken him to the final stage of the 2017 Caputo Cup, a prestigious pizza competition. The starter, which Lawrence-Grant keeps unrefrigerated and has fed frequently with flour for the last 35 years, originally belonged to one of his business partners’ great-great-grandfathers. “He received [it] as a gift from family in the Alaskan Gold Rush,” he says.

Lawrence-Grant says he didn’t know that he possessed one of the oldest starters in the world. “When I competed for best pizza in the United States, I was surprised that no one else used a starter like I did,” he says.

The starter that Ione Christensen uses to make waffles and bread every week is among the oldest in Whitehorse. “The age of my sourdough and that it has been in the same family for 120 years seems to be what makes it so interesting and unusual for people,” she says.

At the end of breakfast, De Smedt packed a sample of Christensen’s sourdough inside a chilled bag designed to cool the starter and slow the fermentation, which keeps the strain healthy in a state of near-suspended animation for up to 96 hours. Back at the library, he separated out part of the strain and placed it in a styrofoam box chilled to about 39℉ to send to Professor Gobbetti’s laboratory. The otheran off-white paste studded with bubbleshe put into a new jar that he slid into place on a brightly illuminated, chilled shelf. Its label reads #106.

“Finding sourdough is a bit of an adventure,” De Smedt says. “But it’s a way of helping to rescue these stories. After all, more than distinct flavors, aromas and biochemical characteristics, what we keep in each of these jars is nothing less than history.”