DNA tests reveal what's living in Yukoner's 120-year-old sourdough starter

Some of Ione Christensen's prized sourdough starter is now in a Belgian sourdough library where tests were done to try to determine its chemical makeup and its history.

A sample of Ione Christensen's prized starter now in Belgian sourdough library

'DO NOT THROW OUT,' reads the label on a container in Ione Christensen's fridge in Whitehorse. The sourdough starter dates to the Klondike Gold Rush. (Kiyoshi Maguire/CBC)

Ione Christensen pulls a small Tupperware from her fridge at home in Whitehorse. The container is beaten up and the contents look like a paste that may have gone bad. It looks questionable, even a little cruddy. 

Inside is something special — a 120-year-old sourdough starter.

A label on the container reads, "DO NOT THROW OUT."

"The reason I do that is because if we're going away ... and someone was looking after the house, you don't want them cleaning out the fridge before you come home and say, 'that's a horrible looking thing,'" said Christensen, a former Yukon senator.

The starter has been in Christensen's family since the 1898 Klondike Gold Rush, when her great-grandfather travelled to Dawson City via the Chilkoot Trail.

A line of stampeders ascend the grueling Chilkoot Trail, en route to the Klondike goldfields. (Seattle, Wash. LaRoche/Library and Archives Canada)

A year ago, part of Christensen's prized starter got packed up in a special box and shipped to Saint-Vith, Belgium, to become sample 106 in the Puratos Sourdough Library.

Some of the starter has gone on display in the library, and tests were also done to find out what microorganisms are thriving in the sourdough that Christensen, 85, uses each weekend to make fluffy and flavourful waffles and hot cakes. 

Isolating and identifying the bacteria and yeast living in a starter can help bakers make healthier and better-tasting bread, says Karl de Smedt, sourdough librarian at the Belgian facility.

Now, after months of testing, the results from Christensen's starter are back.

Searching for the missing link

The tests can't solve one mystery — where Christensen's starter actually started. 

She knows her great-grandfather had the starter when he reached Dawson City, but she doesn't know where he picked it up along the way. 

Christensen with Karl de Smedt, who collects samples of sourdough from around the world, tests and studies them, then stores them in at the Puratos Sourdough Library in eastern Belgium for the future. (Jane Sponagle/CBC)

"I somehow just can't see five men leaving home and saying, 'Oh! We have to take our sourdough,'" said Christensen, referring to her great-grandfather and his brothers, who left New Brunswick together in search of Klondike gold.

She has often thought her great-grandfather got the starter in Dyea, Alaska, just before going over the Chilkoot Pass.

Many Klondike stampeders relied on their ball of sourdough starter as they made the long journey to Dawson City. Those who survived a winter in Yukon earned the nickname "Sourdough."

Christensen's starter could have a link to San Francisco, which has its own connection with gold miners, and sourdough.

The yeast found in Christensen's sourdough is from the same genus of yeast in many San Francisco sourdoughs.

'It's all about the eating,' says Christensen.  (Jane Sponagle/CBC)

"It's like saying it's a dog, but what kind of dog? It can be a German shepherd or a Chihuahua or something in between," said de Smedt, over Skype from Las Vegas, where he was attending the International Baking Industry Exposition. 

De Smedt says more tests are needed to confirm the yeasts have the same DNA. 

"Historically, we know that a lot of people who were in the California Gold Rush in 1849 went to the North, but to really track it down we don't have enough data," said de Smedt. 

He says the library needs more Gold Rush-era samples that "could unveil these secrets."

Limited tests

"I don't really understand all of it," Christensen admits, looking over the starter test results at her kitchen table.

The Sourdough Library's lab can do a limited number of tests, like determining the sourdough starter's acidity. Christensen's sourdough is most acidic in the collection. 

De Smedt says that can be explained by the fact that Christensen is not a professional baker, so she is not feeding and using her starter every day. Plus, she stores her sourdough in the fridge.

Christensen, a former Yukon senator whose great-grandfather came to Yukon during the Klondike Gold Rush, makes sourdough bread and pancakes each weekend. (Jane Sponagle/CBC)

"When you keep your starter in the fridge, you give the microorganisms the chance to acidify and acidify and acidify," said de Smedt.

Part of the starter was shipped to the University of Bari in southern Italy for DNA tests. Researchers found three types of bacteria and only one type of yeast. 

Christensen is happy to know more about the science behind her sourdough starter, but she also remembers what's most important. 

"It's all about the eating," she said. 


Jane Sponagle is reporting in Halifax for the summer of 2022. She is also the Current Affairs producer for CBC Yukon based in Whitehorse. Over the past 10 years, Jane has lived and reported in all three territories.


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