The World’s Oldest Leavened Bread Is Rising Again

This is the story behind the breads you might be baking in lockdown

Google searches for terms like "sourdough," "bread recipe" and "banana bread" skyrocketed in the middle of March. Chris R. Sims via Wikimedia Commons under CC BY-SA 4.0

With the majority of Americans under some variation of stay-at-home orders, many are searching for indoor hobbies to fill their time. Baking, a pastime with a tangible—and tasty—reward, is one such option. And as evidenced by Google Trends, homemade bread in particular has experienced a recent surge in popularity.

Most bread recipes require just a few common ingredients, but baking a toasty loaf from scratch is still a lengthy process. Waiting for yeast bread dough to rise can take hours of patience; for those craving tangy sourdough, the process lasts even longer, as aspiring artisans must grow a starter, or collection of yeast and other microbes living and fermenting in a solution of flour and water.

“The fermentation that occurs after a few days gives the starter its sour smell,” explained Sharon Vail for NPR in 2006. “Then it’s ready to use, for years if treated with respect.”

Sourdough starters have accompanied people on an array of adventures. According to one legend, reported Kat Eschner for Smithsonian magazine in 2017, Christopher Columbus brought a starter with him to America but found the continent lacked the wheat and yeast necessary to complete the recipe. America’s actual sourdough culture started later, when miners reached San Francisco during the Gold Rush of the mid-1800s.

Sourdough bread starter
A sourdough bread starter Andersbknudsen via Flickr under CC BY-2.0

Prospectors brought bread starters on their gold-hunting treks, even sleeping near the concoctions at night to keep them warm when temperatures fell. But in the new microbial landscape, the starters changed, giving the bread more sour, tangy and chewy characteristics.

“Local bakers swore that no one could reproduce it outside a 50-mile radius of the city,” wrote Patricia Gadsby and Eric Weeks for Discover magazine in 2003. “When they gave dough to bakeries elsewhere, it inexplicably lost its ‘sour.’”

Decades ago, researchers identified the microbes that make San Francisco sourdough special: The yeast is Candida milleri, and the principal bacterium is Lactobacillus sanfranciscenis.

The loaf’s latest revival also started in California’s Bay Area. As Zoe Williams reported for the Guardian in 2019, meticulously supported sourdough starters became a common pastime in Silicon Valley, and the hobby quickly radiated outward. Further south, in Pasadena, physicist and Xbox inventor Seamus Blackley has been reviving some of humanity’s earliest sourdoughs.

Last April, Blackley baked loaves with strains of yeast he reported were more than 5,000 years old. After facing criticism over the yeast’s “questionable provenance,” in the words of Atlas Obscura’s Luke Fater, the inventor teamed up with University of Iowa biologist Richard Bowman and University of Queensland Egyptologist and archaeologist Serena Love to more accurately recreate ancient Egyptian sourdough. (Blackley has continued baking bread amid the COVID-19 pandemic, most recently following a recipe that came, in part, from hieroglyphs.)

To aid Blackley’s quest for ancient sourdough, Love developed non-invasive techniques that she used to extract dormant yeast spores from Egyptian artifacts kept at Boston’s Museum of Fine Arts and Harvard’s Peabody Museum of Archaeology and Ethnology. Blackley and Bowman grew the yeast in a starter supported by Emmer flour, a dense variety Egyptians likely used in the Old Kingdom, after modern nutrients kept killing yeast samples.

Blackley then fermented the yeast at 94 degrees Fahrenheit—“the average daytime temperature around the Nile, and it makes bangin’ bread,” he tells Atlas Obscura—and baked more than 70 practice loaves before moving on to traditional baking methods that Love deduced through archaeological research. He baked the final loaf in a cone-shaped clay bedja pot buried in a hole and surrounded by embers.

The timing of homemade bread’s social media-fueled resurgence is perhaps a touch ironic. Passover, the Jewish festival held to commemorate the Israelites’ emancipation from slavery in ancient Egypt, is set to begin this Wednesday. During the eight-day holiday, Jews are barred from eating leavened bread; instead, many will dine on unleavened matzo bread.

Those not celebrating Passover—or hoping to bake exclusively with ancient spores—have plenty of options for getting started with sourdough. Freely available guides for sourdough starters begin with a mix of equal parts water and flour. Set out in a warm place, the solution will catch wild yeast that floats in the air. With a few days of care, the starter is ready for use.

“It’s not surprising that people are turning toward baking bread as a release,” writes Grace Z. Li for SF Weekly. “Baking bread is cheap, it’s time-consuming, it’s indoors, it’s useful, and it’s as healthy as its add-ons will be. It even feels like an absurd luxury. Baking bread—especially on a weekday—requires time and energy, and it engenders an idyllic and reassuring feeling of domestic control.”

Unlike Blackley, Li opted to bake banana bread, another recipe rooted in American history, though much younger than sourdough. Banana bread first emerged in the 1930s, after baking soda and powder became mass produced and the Great Depression pushed people to make use of everything, including overripe bananas. The sweet treat is now one of the most sought-after recipes on King Arthur Flour’s website—and its surge in popularity has actually outpaced sourdough’s in recent weeks.

Get the latest stories in your inbox every weekday.