SAN FRANCISCO, Aug. 16, 2023 — A few years ago, amid lockdown boredom, it seemed like everyone was perfecting their sourdoughs. A simple, fermented mixture of flour and water, the bread is powered by microbes that provide its one-of-a-kind tangy flavor. For over a hundred years, sourdough bread has been synonymous with San Francisco, where today, scientists will report that they’ve identified and quantified 21 key chemical compounds that make this bread taste and smell so unique. They’ve also compared the levels of the compounds in different breads.
The researchers will present their results at the fall meeting of the American Chemical Society (ACS). ACS Fall 2023 is a hybrid meeting being held virtually and in-person Aug. 13–17, and features about 12,000 presentations on a wide range of science topics.
Sourdough breads have existed for centuries, dating back to ancient Egypt — well before they hit their recent peak of popularity in 2020. Unlike other wheat or white breads, which often rely on baker’s yeast to rise, sourdough breads use a “starter” — a living colony of bacteria and wild yeast that causes the bread’s dough to rise through fermentation. Since the microbes come from the air of the local environment, certain places are reportedly home to the best loaves. For example, San Francisco’s unique foggy climate is said to help make its sourdoughs so famously delicious.
Even though these breads are common, little work has been done to understand what chemical compounds provide their characteristic taste and smell. This knowledge could be important to bakers who need to control the quality of their breads, preventing them from becoming too sour, and it could also help them create more consistent sourdoughs for consumers to enjoy. So, Thomas Hofmann’s team at the Technical University of Munich wanted to apply an updated version of a technique known as “sensomics” to sourdough bread crumb — the soft inside part of a loaf. Hofmann currently serves as editor-in-chief of ACS’ Journal of Agricultural and Food Chemistry.
“With sensomics, you can take just a few key compounds and completely recreate the characteristic taste of a food,” says Laura Eckrich, a graduate student in Hofmann’s lab, who is presenting the work at the meeting. The approach involves chromatography, mass spectrometry and similar methods. The team has applied the method previously to other foods to isolate all the flavor-active compounds and to determine their structures and concentrations, as well as how they contribute to taste. The team has used this knowledge to re-engineer the flavor profile of various foods from the bottom up.
Hofmann’s team isolated, identified and quantified the flavor compounds in sourdough bread crumb, and then determined which ones were the most important. The resulting 10 key “tastants” and 11 key “odorants” were then combined into a sourdough “essence,” the flavor of which was confirmed by a human sensory panel. The key taste compounds include salt, which is directly added to the dough, as well as acetic and lactic acid, produced during fermentation. After these experiments, they applied a technique called “unified flavor quantitation,” which was previously developed by Hofmann’s team, to the sourdough bread. For the first time, this technique allowed them to analyze these unique taste and aroma compounds simultaneously.
The team then used the method in brand-new studies to quantify the concentrations of these compounds in different types of bread. They collected both yeast-based and sourdough breads from local bakeries and supermarkets made with either rye or wheat flours. Though key sourdough compounds, including lactic and acetic acids, were found in the yeast-based breads, they were present in much smaller amounts. These results confirmed the importance of the fermentation process to the sourdough’s special flavor.
Next on the researchers’ plates was an analysis of the best way to reduce the salt content in breads. They addressed this issue by unevenly distributing saltier doughs throughout a dough mixture. Since breads, especially sourdoughs, can contribute significantly to one's daily salt intake, the method could help reduce the amount of sodium while maintaining the bread’s unique taste.
Ultimately, the team says their discoveries should be welcome news for the baking industry. “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,” says Eckrich.
The researchers acknowledge support and funding from the German Research Foundation.
A recorded media briefing on this topic will be posted Wednesday, Aug. 16, by 10 a.m. Eastern time at www.acs.org/acsfall2023briefings. Reporters can request access to media briefings during the embargo period by contacting newsroom@acs.org.
For health and safety information for ACS Fall 2023, please visit the FAQ webpage.
FAQs
The key taste compounds include salt, which is directly added to the dough, as well as acetic and lactic acid, produced during fermentation.
What makes sourdough bread sour? ›
Sourdough bread's signature taste comes from friendly bacteria and yeast, which produce flavorful lactic and acetic acids in rising bread dough.
What makes San Francisco sourdough so sour? ›
Why? Well, according to the museum, Boudin bread owes its special flavor to a strain of bacteria that thrives only in San Francisco's climate. Scientists identified it here in 1970, so they named it Lactobacillus sanfranciscensis.
Why did sourdough become so popular? ›
The popularity of sourdough is understandable. We know that it tastes great and has a unique flavor that can't be replicated with other types of bread or baked products. We also know that it is relatively easy to make although it does take a lot of time.
What is so special about sourdough bread? ›
Sourdough relies on a mix of wild yeast and lactic acid bacteria, rather than baker's yeast, to leaven the dough. It's richer in nutrients, less likely to spike your blood sugar, contains lower amounts of gluten, and is generally easier to digest than bread made with baker's yeast.
Why is store bought sourdough so sour? ›
One consequence of the common belief that sourdough should be sour is that commercial sourdough is too sour. Sadly, most commercial sourdoughs aren't actually sourdough breads. They are yeasted breads that have had acetic acid, malic acid, and/or fumaric acid added to them.
Why does my sourdough smell so sour? ›
A healthy, well-fed sourdough starter typically has a pleasant, slightly sour smell. This aroma is often compared to yogurt or buttermilk, indicating a good balance of yeast and lactic acid bacteria. It's the smell of fermentation in full swing, a sign that your starter is ready to leaven a loaf of bread.
What makes those pandemic era sourdoughs so deliciously uniquely sour? ›
The key taste compounds include salt, which is directly added to the dough, as well as acetic and lactic acid, produced during fermentation.
Why is everyone making sourdough bread in 2024? ›
For many folks, the renewed interest in sourdough is health-related. Some are going even further than baking their own bread: They're milling their own flour from whole wheat berries, too.
What bacteria makes sourdough sour? ›
The yeasts cause the dough to rise by creating carbon dioxide bubbles, while the lactic acid bacteria provide the sour flavor (in the form of acetic acid and lactic acid) and preserve the bread by lowering its pH, which prevents the growth of food borne pathogens.
May support gut health
Although the beneficial microbes in the starter tend to be lost during the baking process, the fibre and plant compounds, called polyphenols, become more bio-available. These act as an important fuel source for our gut microbes, which explains why sourdough is a gut-friendly choice.
What is with the sourdough trend? ›
Health and Wellness Focus: Sourdough's potential digestive benefits and lower glycemic index compared to some white breads resonate with health-conscious consumers. Versatility and Innovation: Sourdough's ability to be used in various baked goods, from baguettes to pastries, expands its market appeal.
What's the rage about sourdough bread? ›
Why is sourdough good for me? One of the big benefits of sourdough over commercially-baked bread is that, thanks to the fermentation process, it's easier to digest.
Why do people like sourdough so much? ›
Sourdough breads are very aesthetically pleasing. The yeast used in them has a lot of time to properly ferment, which leads to a great-tasting dough filled with air bubbles. After baking, the bread then reveals a beautiful cross section much like those we see in well-made croissants.
Is sourdough actually healthy? ›
Sourdough has made a comeback—and for good reason. It provides nutrients, including healthy carbs, protein, fiber, iron and vitamins like folic acid. It may help improve digestion, lower chronic disease risk and even promote healthy aging.
Is sourdough good for your gut? ›
Sourdough bread may be easier to digest than white bread for some people. According to some studies, sourdough bread acts as a prebiotic, which means that the fiber in the bread helps feed the “good” bacteria in your intestines. These bacteria are important for maintaining a stable, healthy digestive system.
How do you get the sour taste out of sourdough bread? ›
Adding baking soda. Adding a pinch of baking soda makes your coffee less acidic. Likewise, it makes sense that adding a bit of baking soda to your bread dough will also decrease the sourness of the final bread. As an added benefit, it will help make your dough rise more (check out my sourdough soda bread recipe).
Why is it called sourdough if it's not sour? ›
Sourdough bread is called “sourdough” because it is made using a naturally occurring yeast and bacteria culture known as a sourdough starter. The starter is a mixture of flour and water that is left to ferment over time, which allows wild yeast and bacteria to colonize it.
Is sourdough healthier than white bread? ›
The bottom line. Sourdough is a healthier alternative to regular white or whole wheat bread. Although it has comparable nutrients, the lower phytate levels mean it is more digestible and nutritious. The prebiotics also help to keep your gut bacteria happy, and it may be less likely to spike blood sugar levels.
What's the difference between sourdough and sour bread? ›
Regular Bread vs Sourdough Ingredients
Regular bread uses a commercial yeast culture while sourdough varieties use a culture of natural yeast and lactobacilli bacteria that creates lactic acid, which in turn creates the sour flavor.
