Understanding Why Dough Becomes Sour

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If you’ve ever made bread with a sourdough starter, you may have noticed a distinct tang in the finished product. This flavor is the result of dough fermentation – a process by which microorganisms break down carbohydrates and produce organic acids. In this article, we will explore the science behind dough fermentation and what factors contribute to the sourness of sourdough bread.

The Science Behind Dough Fermentation

Dough fermentation is a complex process that involves multiple microorganisms, including bacteria and yeast. During fermentation, the yeast consumes the sugars in the flour and produces carbon dioxide gas, which causes the dough to rise. At the same time, bacteria in the dough produce lactic acid through a process known as lactic acid fermentation. The lactic acid gives sourdough bread its distinct sour flavor.

The type and amount of microorganisms present in the dough can vary based on a variety of factors, including the environment, the ingredients, and the preparation method. Understanding these variables is essential to producing flavorful, consistent sourdough bread.

Factors That Contribute to Sour Dough

There are several factors that can contribute to the sourness of sourdough bread:

  • The type and quantity of microorganisms present in the dough. Different strains of bacteria and yeast can produce varying amounts of lactic acid, which affects the flavor of the bread.
  • The temperature at which the dough is fermented. Lower temperatures can slow down the fermentation process and produce a milder flavor, while higher temperatures can speed up fermentation and result in a stronger sour flavor.
  • The ratio of flour to water in the dough. A higher hydration level can promote the growth of bacteria and result in a more acidic flavor.
  • The amount of time the dough is allowed to ferment. Longer fermentation times can result in a more complex flavor profile, while shorter fermentation times can produce a milder flavor.

The Role of Microorganisms in Dough Fermentation

As mentioned earlier, both yeast and bacteria play a crucial role in dough fermentation. Yeast is responsible for carbon dioxide production, which makes the dough rise. Bacteria, on the other hand, produce lactic acid, which gives the bread its sour flavor. The most common strains of bacteria found in sourdough bread are lactobacillus and pediococcus, both of which thrive in acidic environments.

It’s worth noting that not all bacteria are created equal when it comes to sourdough bread. Some strains of bacteria are more effective at producing lactic acid, while others may produce unwanted flavors or aromas. Therefore, it’s essential to maintain a healthy sourdough starter by feeding it regularly with the right type and amount of flour and water.

How Temperature Affects Dough Fermentation

The temperature at which dough is fermented can have a significant impact on the resulting flavor of sourdough bread. Generally, fermentation is slower at lower temperatures and faster at higher temperatures. Therefore, a lower fermentation temperature can produce a milder, less sour flavor, while a higher temperature can result in a stronger sour flavor.

However, it’s important to note that extreme temperatures can also be detrimental to dough fermentation. Fermenting dough at too low a temperature can result in a sluggish rise, while fermenting dough at too high a temperature can cause the dough to overproof and collapse.

The Best Flour for Making Sourdough Bread

The type and quality of flour used to make sourdough bread can also affect its flavor. Many bakers prefer to use bread flour, which has a high protein content that promotes gluten development and gives the bread structure. Others prefer all-purpose flour, which has a lower protein content and can result in a more tender crumb.

Additionally, the type of grain used to make flour can also impact the flavor of sourdough bread. Some bakers prefer to use whole grain flours, which contain the bran and germ of the grain and can produce a nuttier, earthier flavor. Others prefer white flour, which has had the bran and germ removed and can result in a milder flavor.

The Importance of Hydration in Sourdough Starter

Hydration refers to the ratio of water to flour in the sourdough starter. Maintaining the right hydration level is crucial to the health of the starter and the resulting bread’s flavor. Generally, a higher hydration level can promote the growth of bacteria and produce a more acidic flavor. However, a lower hydration level can result in a slower fermentation process and a milder flavor.

Many bakers prefer to use a 100% hydration sourdough starter, which means equal parts flour and water by weight. However, the optimal hydration level can vary based on the baker’s preference and the recipe being used.

Creating the Perfect Environment for Dough Fermentation

The environment in which dough is fermented is also essential to producing flavorful sourdough bread. A warm, humid environment is optimal for the growth of yeast and bacteria. Therefore, many bakers prefer to ferment their dough in a warm, draft-free place, such as an oven with the light on or a proofing box.

Additionally, it’s important to provide the dough with enough time to ferment properly. Generally, sourdough bread requires a longer fermentation time than bread made with commercial yeast. Therefore, it’s essential to plan ahead and allow enough time for the dough to rise and develop flavor.

Techniques for Developing Flavorful Sourdough Bread

There are several techniques bakers can use to develop more flavorful sourdough bread:

  • Use a sourdough starter that has been fed regularly and is healthy.
  • Experiment with different fermentation temperatures to find the optimal temperature for the desired flavor.
  • Add other ingredients, such as herbs or cheese, to the dough for added flavor.
  • Use a long fermentation time to allow the dough to develop a more complex flavor profile.
  • Develop the gluten in the dough fully to create a better structure for holding in flavor.

The History and Culture of Sourdough Bread-making

Sourdough bread-making has a rich history dating back thousands of years. It was the primary bread-making method in ancient Egypt, Greece, and Rome. During the California Gold Rush in the mid-1800s, sourdough bread became popular among miners due to its portability and long shelf life.

Sourdough bread-making has also become an important cultural icon in the United States, particularly in San Francisco. Many bakers in the city still make sourdough bread using traditional methods and techniques.

Common Mistakes to Avoid When Making Sourdough Bread

While sourdough bread-making can be a rewarding process, there are several common mistakes that new bakers should avoid:

  • Not maintaining a healthy sourdough starter
  • Using the wrong type or amount of flour
  • Not allowing enough time for fermentation
  • Fermenting dough at the wrong temperature
  • Overworking the dough and breaking down the gluten

Troubleshooting Common Issues with Sourdough Bread

Even the most experienced bakers can run into issues when making sourdough bread. Here are some common issues and their solutions:

  • The bread is too sour – adjust fermentation time and temperature to produce a milder flavor
  • The bread is not rising – check the freshness of the yeast or adjust the fermentation temperature
  • The crust is too hard – reduce oven temperature or cover bread with foil while baking
  • The crumb is too dense – allow more time for fermentation or increase hydration level

Comparing and Contrasting Different Styles of Sourdough Bread

There are many different styles of sourdough bread, each with its unique flavor and texture profile. Some popular styles include:

  • San Francisco-style sourdough – a classic style with a tangy, sour flavor
  • French-style sourdough – a milder, more delicate sourdough bread
  • Country-style sourdough – a hearty, rustic bread with a dense crumb

Each style of sourdough has its unique characteristics, and bakers can experiment with different styles to find their favorite.

Nutritional Benefits of Eating Sourdough Bread

Sourdough bread has several nutritional benefits compared to other types of bread. Firstly, the long fermentation process breaks down gluten, making sourdough easier to digest for those with gluten sensitivities. Additionally, the lactic acid produced during fermentation can improve gut health by promoting the growth of beneficial bacteria.

Sourdough bread also contains beneficial nutrients, such as B vitamins and minerals like iron and selenium. Therefore, it can be a healthier alternative to processed bread products.

Tips for Maintaining and Storing Your Sourdough Starter

Keeping a healthy sourdough starter is crucial to making flavorful sourdough bread. Here are some tips for maintaining and storing your sourdough starter:

  • Feed your starter regularly, ideally once a day
  • Use a kitchen scale to measure the flour and water accurately
  • Store your starter in the refrigerator between uses (it will keep for several weeks)
  • Take your starter out of the refrigerator and feed it at least a day before using it to make bread

With proper maintenance, a sourdough starter can last for years, producing countless loaves of flavorful bread.


In conclusion, understanding the science behind dough fermentation is essential to producing flavorful, consistent sourdough bread. By optimizing factors such as temperature, hydration, and fermentation time, bakers can create bread with a wide range of flavors and textures. Additionally, maintaining a healthy sourdough starter is crucial to successful bread-making. Ultimately, the key to producing great sourdough bread is experimentation and practice. With time and patience, anyone can master the art of sourdough bread-making.