Instead of books, the Puratos World Heritage Sourdough Library in Saint Vith, Belgium houses jars of sourdough starter.
fresh sourdough right out the oven
Credit: Justin Sullivan / Getty Images

How does one memorialize food, that temporal, ephemeral thing? In the case of Nancy Silverton’s famous sourdough, born of the yeast of Concord grapes, one puts its starter in a library—of sorts. The Puratos World Heritage Sourdough Library in Saint Vith, Belgium houses glass jars instead of books, all lined up in hushed temperature controlled vaults. Inside, refrigerator-like glass cases—not unlike what you’d see at the grocery store—are clinically clean. They house 84 starters in total, sourced from all over the world.

And Nancy Silverton’s, which has been housed at the project for four years and counting, was grown in L.A. and cold FedExed to Belgium. While Los Angeles isn’t known for its sourdough, it is Silverton’s version that infamously beat out all all its San Franciscan compatriots in a blind taste test conducted by the San Francisco Chronicle, an upset to the city that's arguably synonymous with the art form.

Every year, Silverton’s starter in Belgium has to be fed by more starter that La Brea Bakery ships over. (It should be noted that the company is no longer owned by Silverton; it was sold to Swiss-based Aryzta in 2001, which also owns brands like Otis Spunkmeyer.)

Nancy Silverton sourdough starter
Credit: La Brea Bakery

So, what’s the point of a sourdough starter library, besides the cool factor and positive PR for Puratos, a Belgium-based international baking company? Well, finding out what makes sourdough taste like sourdough—and what makes Silverton’s among the best. While sourdough cemented its stronghold of American culture when miners brought starters with them to San Francisco—reportedly hugging them in glass jars at night to keep them warm—its fermented strains are far more ancient. Its fabled origins hearken in Egypt, where it’s said to have arisen 6,000 years ago.

As with anything so storied, so complex, and so beloved as sourdough—Sourdough Sam as the 49ers mascot epitomizes this reverence as well as anything could—there are mysteries. There are debates.

Some people hold that you simply cannot replicate San Francisco-style sourdough beyond the reaches of the area. It just doesn’t taste the same. “When they gave dough to bakeries elsewhere, it inexplicably lost its ‘sour,’” reported Discover Magazine.

Others disagree. San Francisco starter, they hold, really comes down to the presence of a very specific bacteria. It is actaully named L. sanfranciscensis, after the city of its prevalence.

The bacteria isn’t just found in sourdough that comes from San Francisco, however—it’s been found elsewhere, so it’s not some magical phenomenon that materializes only within city limits.

Still, it is contentions and mysteries like these that make the phenomenon of sourdough so beguiling, and invite its research. At the Puratos project, professor Marco Gobbetti has been studying the starters for their micro-organisms, wild yeast, and strains of lactic bacteria, hoping to glean something on the science of deliciousness.