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How Does Sourdough Get Its Unique Flavor?


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By Jodi Helmer

Your sourdough starter has terroir—and researchers at NC State University are determined to understand it. Its Sourdough Project collected 550 sourdough starters from around the world and analyzed the micro-organisms found in each sample to determine how the environment affects wild yeast and lactic and acetic acids that give the starter its unique flavor.


"There is this really cool thing happening where initially identical microbes evolve as they're sent out into different environments," explained Benjamin E. Wolfe, an assistant professor at Tufts University and part of the team working on the Sourdough Project at NC State. "The bacteria start to change, integrating foreign elements into their genomes really quickly."

The Massachusetts Institute of Technology (MIT) launched a similar citizen science project last spring, dubbed "The Herman Project." Researchers shared a sourdough starter, named Herman, with bakers and tracked its path from person to person to see how microbes change in different environments. To date, researchers have sent 150 starters to 10 countries; more than half have been returned to the MIT lab for analysis.

"We're starting to appreciate the role of whole communities of diverse micro-organisms, like the gut microbiome, and how microbes in the soil provide essential nutrients to the plant in agriculture," said Gabriel Leventhal, a postdoctoral fellow at MIT and founder of The Herman Project. "Fermented foods like sourdough are particularly interesting because, as humans, we have been cultivating these 'microbial communities' for thousands of years. There are many stories about sourdough starters that have been propagated for decades—even centuries—and handed down through generations, but we know very little about the internal composition of the microbial community. This is where The Herman Project comes in."

The initial results from both MIT and NC State show that the microbial makeup of a sourdough starter changes based on multiple factors in the environment—from elevation to temperature to a baker's skin—and it affects everything in the resulting bread, from aroma to flavor. It appears that the differences start in the field.

As part of a 2015 study, researchers grew wheat on one farm using four different farming methods (conventional, organic with cow manure, organic with green manure, and zero inputs) and found marked differences in the microbes in the flours. Farming methods also had an effect on the bread—breads made from organic flours had a superior crumb structure and crust color.

Wolfe calls this farm-to-ferment effect an important consideration when choosing flour for a sourdough starter. "Different kinds of flour create different microbial communities," he said.

Although researchers on The Sourdough Project have just started assessing the microbes in various starters, one controversial finding has emerged: "There is nothing unique about San Francisco sourdough—no unique microbial signature that we've found so far—that makes it any different from sourdough from Boston or Quebec," said Wolfe. "We're still looking."

Reposted with permission from our media associate Modern Farmer.

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