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Why Does Sourdough Have Such a Unique Flavor?

A sourdough loaf dusted with flour in a heart shape on a white and blue tea towel.
Credit: Mirka/ Pixabay
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A staple of lockdown kitchens and bakeries across the world, sourdough is famed for its unique, tangy flavor. New research, presented at the American Chemical Society (ACS) Fall 2023 conference, has identified what makes sourdough taste so good.

The importance of the starter

The wild yeast and microbes found in the starter of a sourdough cause the bread to rise by consuming the carbohydrates in the flour and producing carbon dioxide, which gives the bread its characteristic airy texture. Early sourdough research revealed that over 50 types of lactic acid bacteria and over 20 species of yeast can thrive in sourdough starters.

As the starter uses wild yeast and microbes, starters across the world can vary. San Francisco is particularly famed for its sourdough, with some bakeries using the same starters in their recipes for around 170 years. It has been rumored that the foggy environment of the city plays a role in the taste of the sourdough, with the loaves once thought to contain a unique bacterium dubbed Lactobacillus sanfranciscensis, which was later found across the world.

The essence of sourdough

The taste of sourdough can be influenced by factors including fermentation time, temperature and flour type, as well as the microbes present in the starter.

A research team has identified the compounds responsible for sourdough's unique taste, finding 11 odorants and 10 tastants using a technique called sensomics.

“With sensomics, you can take just a few key compounds and completely recreate the characteristic taste of a food,” said Laura Eckrich, who presented the team’s research at ACS Fall 2023.

Sensomics uses data from chromatography, mass spectrometry and other techniques to isolate and quantify key molecules from food – in this case, the crumb of the sourdough – enabling researchers to piece together the food’s “essence”.

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The sourdough essence was then confirmed to match the smell and taste of sourdough bread by a human sensory panel.

The key tastants in sourdough include salt, acetic acid and lactic acid. Salt is added to the loaves by the baker, but acetic and lactic acids are the byproducts of fermentation. The researchers then compared the concentrations of these compounds in sourdough with yeast-based breads, made with either rye or wheat flour.

Although yeast-based breads did contain lactic and acetic acids, they were present in much lower concentrations than in sourdough, confirming the importance of the fermentation process for developing flavor in a sourdough loaf.

Of benefit to bakers

This new research could help bakers control the quality and consistency of their loaves and prevent waste from loaves that are too sour. It can also help optimize the amount of salt bakers add to their sourdough.

“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,” said Eckrich.

Reference: Amann LS, Frank O, Dawid C, Hofmann TF. The sensory-directed elucidation of the key tastants and odorants in sourdough bread crumb. Foods. 2022;11(15):2325. doi: 10.3390/foods11152325

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