Sourdough and bread in general has been a staple food for all of human history. Cereals such as wheat and rye were some of the first crops to be domesticated by early agricultural groups as many as 10,000 years ago, and these grains were used to make bread. The first documented production of sourdough bread came a few millennia later in Egypt, likely around 1500 BC. Egyptians realized that when flour and water were left out long enough to ferment, the resulting dough increased in volume and was able to be baked into bread.
The Jewish people learned this process of making sourdough bread in Egypt and took that knowledge with them when they fled the region. From this period on, sourdough spread throughout Europe and the Middle East, becoming a staple food and growing in social significance until baker’s yeast was introduced in the mid-1800s.
Sourdough was a staple food in France throughout the Middle Ages. Sourdough was easy to make to both bakers and households because its acidity reduced the need for salt, an expensive and highly taxed commodity at the time. By the 17th century, cultural tastes started to shift away from sour foods, leading the way to new backslopping techniques. Backslopping is when a small part of the original sourdough starter is fed flour and water to grow new sourdough, stabilizing the acidity of the starter. In contrast, German bakers in the 20th century started using rye flour in sourdough as an acidifying agent. Rye sourdough bread further spread through the Scandinavian and Baltic countries as well.
Sourdough also became popular in the United States. During the California and Klondike gold rushes, sourdough was a staple food of gold miners because of its long shelf life and use as a leavening agent. Sourdough continues to be popular in these areas today, and some bakeries claim that their sourdough is the same strain that was used 150 years ago.