Does Sourdough Bread Produce Lactic Acid?

December 19, 2025 •

4 min read

The symbiotic culture of wild yeast and lactic acid bacteria (LAB) is responsible for the unique fermentation process that creates sourdough. This fermentation, a key stage in the process, results in the bread producing lactic acid, which significantly influences the final product's flavor, texture, and nutritional properties.

Quick Summary

During sourdough fermentation, lactic acid bacteria convert sugars into lactic acid, contributing to the bread's sour tang, extended shelf life, and improved digestibility.

Key Points

Lactic Acid is a Natural Byproduct: The fermentation process in sourdough produces lactic acid through the metabolic activity of lactic acid bacteria (LAB).
Bacteria Create the Sour Flavor: LAB, particularly Lactobacillus species, consume sugars in the flour and convert them into lactic and acetic acids, which give sourdough its characteristic tangy taste.
Temperature and Hydration Influence Flavor: Warmer temperatures and higher hydration levels favor lactic acid production, resulting in a milder, creamy tang. Cooler temperatures and stiffer doughs lead to more acetic acid, producing a sharper, more vinegary flavor.
Lactic Acid Improves Texture: The acidic environment created by lactic acid strengthens the dough's gluten network, helping to create a more voluminous and airy crumb structure.
Acidity Boosts Shelf Life and Nutrition: The low pH from lactic acid production inhibits mold and spoilage, while also neutralizing phytic acid to increase mineral absorption and improve digestibility.
Distinct from Commercial Yeast: Sourdough's complex flavor and nutritional profile are the result of a symbiotic culture of wild yeast and multiple LAB strains, unlike commercial bread which relies on a single yeast strain.

The Symbiotic Relationship of Sourdough Fermentation

Sourdough is a natural leavening agent created from a symbiotic culture of wild yeast and lactic acid bacteria (LAB). This diverse microbial community ferments the sugars found in flour to produce a range of compounds, including acids and gases, which transform simple dough into a complex, flavorful loaf. While the wild yeasts produce carbon dioxide for leavening, the LAB are responsible for producing a variety of organic acids, most notably lactic acid and acetic acid.

This fermentation process is not only crucial for the bread's distinctive sour flavor but also offers several nutritional and technological benefits. The interplay between yeast and bacteria, influenced by factors like temperature and hydration, dictates the final characteristics of the bread, making each sourdough unique.

The Role of Lactic Acid Bacteria in Sourdough

Lactic acid bacteria (LAB) are the key players behind the production of lactic acid in sourdough. These bacteria, predominantly from the Lactobacillus species, are more numerous than the yeasts in a sourdough starter. Their metabolic activity is critical for acidifying the dough, which impacts everything from flavor to preservation.

The LAB population can be broadly classified into two groups based on their fermentation pathways:

Homofermentative LAB: These bacteria primarily convert sugars into lactic acid. They tend to thrive at warmer temperatures, producing a milder, creamier sour flavor.
Heterofermentative LAB: These bacteria produce lactic acid, acetic acid, and carbon dioxide. They prefer cooler temperatures, leading to a sharper, more vinegary tang due to the acetic acid.

The balance of these two types of bacteria, along with the wild yeast, determines the final flavor profile and texture of the bread. A mature and stable starter culture typically contains a dominant population of heterofermentative LAB, contributing a more pronounced sourness over time.

How Lactic Acid Influences Bread Characteristics

The lactic acid produced during fermentation has a profound effect on the final bread product. Its influence extends far beyond just the taste, impacting the dough's structure, the bread's shelf life, and its nutritional value.

Flavor Development: The presence of lactic acid is the primary reason for the quintessential tanginess of sourdough bread. A higher concentration of lactic acid results in a milder sourness, often described as yogurty, while a higher ratio of acetic acid contributes a more pungent, vinegary bite.
Dough Structure and Texture: Lactic acid strengthens the gluten network in the dough, improving its elasticity and gas retention. This enhanced gluten structure, combined with the carbon dioxide produced by yeast and heterofermentative LAB, leads to the airy, open crumb and crisp crust that sourdough is known for. The acidic environment also activates enzymes that further break down flour proteins, resulting in a more tender and palatable crumb.
Preservation and Shelf Life: The acidic environment created by lactic acid production creates an inhospitable environment for spoilage-causing bacteria and mold. This natural preservation method extends the bread's shelf life without the need for artificial preservatives.
Nutritional Enhancement: Sourdough fermentation increases the bioavailability of minerals by neutralizing phytic acid, a compound found in grains that can inhibit mineral absorption. The longer fermentation also breaks down gluten and other complex carbohydrates, making the bread easier to digest for some individuals.

Sourdough Fermentation vs. Commercial Yeast Baking


Feature	Sourdough Fermentation	Commercial Yeast Baking
Leavening Agent	A live, symbiotic culture of wild yeasts and lactic acid bacteria.	A single-celled domesticated yeast species, Saccharomyces cerevisiae.
Fermentation Byproducts	Primarily lactic acid, acetic acid, carbon dioxide, and ethanol.	Primarily carbon dioxide and ethanol.
Primary Acid	Lactic acid is the dominant organic acid produced by bacteria.	No significant acid production; requires additional acidulants for flavor.
Flavor Profile	Complex, tangy, and nuanced due to a mix of acids.	More uniform, milder flavor.
Timeline	Longer fermentation times (often 12-48 hours).	Faster process (often 2-4 hours).
Nutritional Benefits	Higher mineral bioavailability, improved digestibility, lower glycemic index.	Lower nutritional benefits compared to sourdough.

The Controlled Variables of Lactic Acid Production

Bakers can influence the flavor profile of their sourdough by manipulating the fermentation conditions to favor either lactic or acetic acid production. A higher ratio of lactic acid to acetic acid (around 4:1 to 10:1) is generally considered ideal for balanced flavor.

Hydration: A more liquid (wetter) starter and dough, with a higher water-to-flour ratio, promotes a higher ratio of lactic acid.
Temperature: Warmer fermentation temperatures (around 86°F or 30°C) favor homofermentative LAB, leading to more lactic acid and a milder flavor. Conversely, cooler temperatures (below 72°F or 22°C) promote heterofermentative LAB, resulting in more acetic acid and a sharper tang.
Flour Type: Whole-grain flours contain a greater variety of microorganisms and minerals, which can promote more complex microbial activity and acid production.

Conclusion

In conclusion, sourdough bread unequivocally produces lactic acid, a critical byproduct of the natural fermentation process driven by lactic acid bacteria. This lactic acid is the central component behind sourdough's distinctive flavor, robust texture, and nutritional advantages, such as improved mineral bioavailability and digestibility. By carefully controlling fermentation factors like temperature and hydration, bakers can manipulate the ratio of lactic to acetic acid to achieve a specific, desired flavor profile. The symbiotic relationship between yeast and LAB is what elevates sourdough beyond standard bread, turning it into a living, complex, and healthy food.

Frequently Asked Questions

Sourdough bread's sour taste comes from the lactic acid and acetic acid produced by lactic acid bacteria during the fermentation of flour. The ratio of these two acids determines the flavor profile, ranging from mild and creamy to sharp and vinegary.

No, the high temperatures of the baking process kill the live lactic acid bacteria and wild yeast in the bread. However, the lactic acid and other beneficial byproducts they produced remain, contributing to the bread's flavor, texture, and nutritional properties.

Yes, the fermentation process in sourdough bread is known to have a lower glycemic index compared to regular bread. The organic acids, including lactic acid, interact with the starches, slowing down the release of sugar into the bloodstream.

You can control the acidity by adjusting your fermentation process. To favor lactic acid for a milder flavor, use a higher hydration starter and ferment at warmer temperatures. For more acetic acid and a sharper tang, use a stiffer starter and ferment at cooler temperatures, such as in the refrigerator.

While the live bacteria are killed during baking, the fermentation process itself produces beneficial postbiotics and prebiotics. Sourdough is considered easier to digest and can promote a healthy gut by nourishing beneficial gut bacteria.

Lactic acid, produced by homofermentative LAB, imparts a milder, creamy acidity, while acetic acid, produced by heterofermentative LAB, provides a sharper, more pungent, or vinegary tang. Both are influenced by fermentation temperature and starter hydration.

To encourage more lactic acid production, use a higher hydration (wetter) starter and ferment it at a warmer temperature, typically around 86°F (30°C). This promotes the activity of lactic acid-producing homofermentative bacteria.