The Science of Sourdough's Unique Flavor Has Been Revealed

Sourdough breads have been baked for thousands of years. Sourdough’s simple recipe, which can be tweaked to produce a deep flavor profile, became a staple of thousands of lockdown kitchens. Now, a new analysis of the interior of the bread has revealed the factors that give sourdough its unique taste.

What makes sourdough unique

Mass-produced wheat and white breads rely on baker’s yeast, the fungus Saccharomyces cerevisiae, to rise. Sourdough, in comparison, uses a combination of wild yeast and microbes to help the bread rise through fermentation. As the microbes seeding the starter are influenced by the microorganisms in their environment, sourdough flavors can vary between locations. In San Francisco, the fog rolling in off the Bay is rumored to harbor microbes that give the city’s bread a cult status. Tartine Bakery, a Bay Area staple that has worn the sourdough crown for years, is popular enough to command a $45 tag for a pair of loaves shipped nationwide. A good starter is big business.

Unlocking the secrets of flavor

Previous studies, including a 1971 paper that turned up a strain of yeast incorrectly thought to be unique to San Francisco, have tried to define the ingredients that make sourdough so popular. But new research, shared by Thomas Hofmann and colleagues from the Technical University of Munich at the fall meeting of the American Chemical Society (ACS), has gone further than any previous work.

The team used an innovative technique called "sensomics" to analyze the soft insides of the bread, which is called the crumb. “With sensomics, you can take just a few key compounds and completely recreate the characteristic taste of a food,” said Laura Eckrich, a graduate student in Hofmann’s lab. The team hopes that their findings could make it easier for bakers to control the flavor profile of their breads and minimize the risk of failed batches that produce too-sour loaves.

Sensomics is a broad term applied to a suite of techniques, including chromatography and mass spectrometry, that allowed the team to identify all the compounds that make up sourdough’s taste and smell, even isolating these molecules’ concentrations and structures.

Distilling a sourdough essence

The researchers identified 21 vital compounds that define sourdough’s taste and smell. Ten of these are “tastants,” and eleven are “odorants.” Using this parts list, the team devised a sourdough “essence”, which matched the profile of the bread itself, as approved by a panel of human smellers and tasters.

Significant compounds that made up this “essence” included salt, lactic acid, and acetic acid – the last two are products of fermentation, while salt is added to the dough during baking. Using a technique called “unified flavor quantitation” developed by Hofmann's team, they simultaneously analyzed the taste and aroma compounds.

This analysis barrage was then aimed at various other bread types, including rye and wheat options from chain supermarkets and artisan bakeries. The team noted that the acids produced during fermentation were also present in these loaves, but at far lower levels, indicating how the unique sourdough fermentation process changes these breads’ flavors.

Getting mo’ from the dough?

The ACS meeting is primarily a show of force to the analytical science community, but Eckrich hopes that their results will help bakers improve their loaves: “This was the first time the key taste and aroma compounds of bread crumb were elucidated using the sensomics approach, and we hope what we learned will help bakers create the best sourdough breads they can.”

Reference: Eckrich L. Flavor elucidation and simultaneous quantitation of key tastants and odorants of sourdough bread crumb. Presented as part of ACS Fall 2023; August 17, 2023; San Francisco, CA.

This article is based on research findings that are yet to be peer-reviewed. Results are therefore regarded as preliminary and should be interpreted as such. Find out about the role of the peer review process in research here. For further information, please contact the cited source.

This article is a rework of a press release issued by the American Chemical Society. Material has been edited for length and content.