Why Does Sourdough Taste Sour?
- Anjali Carl
- May 25
- 2 min read
Pretty much any bakery you may walk into, you will see sourdough bread. And biting into sourdough, you immediately notice that tangy, sour flavor. But what makes sourdough bread sour? It’s simple: bacteria and time.
Unlike “regular” bread which is made with commercial yeast, sourdough bread uses a starter. A starter is a mixture of flour and water that naturally grows wild yeast and bacteria from the surrounding environment. It is a living microbial community where the yeast and bacteria work together during a fermentation process to make the dough rise and create its distinctive flavor. The yeast mostly produces carbon dioxide gas which creates bubbles and helps the bread expand. The bacteria is what creates much of the sour flavor.
Lactic acid bacteria creates lactic acid and acetic acid during fermentation. Lactic acid creates a milder sour flavor whereas acetic acid has more tang, like vinegar. Different doughs and breads have different amounts of each acid which is why sourdough loaves can have different levels of tanginess. While the bacteria drives the flavor, there are a lot of things bakers can do to influence which acid develops more strongly.
Temperature has a big effect on flavor. Warmer temperatures encourage bacteria to produce more lactic acid while cooler temperatures lead to more acetic acid. This is why bakers will refrigerate dough overnight; the colder temperature can help develop a tangier and more complex flavor.
Time also affects sourdough bread. The extra time it takes to make sourdough is important because fermentation continues to develop flavor while dough rests. Sourdough can take over 24 hours to rise. During this time, more acid develops, more flavor compounds form, and the dough structure changes.
Even the type of flour used can change the flavor of sourdough. Whole wheat flour and rye flour ferment more because they have extra nutrients and natural microorganisms. So these flours produce stronger sour flavors than plain white flour. Hydration also affects fermentation. Wetter dough may ferment differently which changes texture and flavor.
And even the starter affects the sourdough flavor. The microorganisms inside a starter are influenced by local air, local water, flour, temperature, and even the baker’s hands. Because of all of these factors, a starter in California will be different from one from Texas or Italy. And keeping a starter alive for years, or decades, will also affect the microorganism composition.
Sourdough is the result of chemistry, biology and baking all in one process. Simple water and flour can turn into a living system that changes flavor based on the local environment.
Anjali Carl is a junior at Cedar Park High School in Cedar Park, Texas. They have been excited about food science since making ice cream in a third-grade science class, and now enjoys baking and recipe development. Through their Girl Scout Gold Award project, they created two cookbooks focused on reducing food waste for food pantries and college students. They plan to study food science and eventually become an ice cream chemist.
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