What Is Sourdough Fermentation?

Sourdough differs from most conventional bread because it does not rely on commercial baker’s yeast for leavening. Instead, it uses a fermented culture called a sourdough starter, made from flour and water, which contains naturally occurring yeasts and lactic acid bacteria.

As the culture ferments, these microorganisms feed on the carbohydrates in the flour. They produce carbon dioxide, which helps the dough rise, along with organic acids that contribute to sourdough’s characteristic tangy flavor and chewy texture.

What Does Fermentation Need?

At its most basic, fermentation requires microorganisms, a source of nourishment, and an environment where those microorganisms can grow.

For example, when making yogurt, Lactobacillus and other beneficial bacteria use lactose—the natural sugar in milk—as a food source. The milk provides both the nutrients and the liquid environment the bacteria need to grow and reproduce.

Sourdough works a little differently.

A sourdough starter contains naturally occurring yeasts and bacteria that are present on flour and in the surrounding environment. When we combine flour and water, we create a moist environment where these microorganisms can thrive.

We then continue feeding the culture with fresh flour and water. The carbohydrates in the flour provide nourishment for the microorganisms, allowing the population to remain active enough to leaven our bread and other sourdough projects.

Once you have an established starter, it can be surprisingly forgiving. The exact amount and timing of feedings can vary depending on how frequently you bake, the temperature of your kitchen, and how active your starter is.

Can Sourdough Starter Go Dormant?

Yes.

If you aren’t baking regularly, you can place your established starter in a clean, sealable container and store it in the refrigerator. The cooler temperature slows fermentation and allows the culture to remain dormant or much less active.

When you’re ready to bake again, the starter can be brought back to room temperature and fed until it becomes active again.

Does Fermentation Break Down Gluten?

Fermentation can partially break down gluten proteins, along with other components of the grain. However, it does not remove gluten completely.

Because of this, traditional wheat-based sourdough bread is not considered safe for people with celiac disease. Even long-fermented sourdough made with wheat, rye, or barley can still contain enough gluten to cause harm.

People who need to avoid gluten should use a properly formulated gluten-free sourdough made with gluten-free ingredients and take care to prevent cross-contamination.

Is Fermented Food Good for Gluten Intolerance?

Fermented foods can be a nutritious addition to many diets, and they can provide live microorganisms and other fermentation products that may support a healthy gut microbiome.

However, it’s important to distinguish between gluten intolerance or sensitivity and celiac disease. Fermented foods do not remove gluten from foods, and there is not enough evidence to say that eating fermented foods can heal celiac disease or reverse the underlying condition.

For people who need to avoid gluten, choosing gluten-free fermented foods can allow them to enjoy the potential benefits of fermentation without consuming gluten.

Fermentation is a beautiful example of how microorganisms, food, time, and environment work together to transform something as simple as flour and water into something entirely different.

And perhaps that is one of the most fascinating things about fermentation: we aren’t doing all of the work ourselves. We are creating the conditions and then allowing nature to do what it does best.