San Francisco sourdough bread is a sourdough bread produced with the use of a starter unique to San Francisco. Contrary to popular belief, San Francisco sourdough bread does not necessarily need to be produced in San Francisco, as the starter can be shipped all over the world, and in fact ordinary bakers can order it through several specialty companies which supply sourdough starter. This style of sourdough has become famous among bread fans, and it is a ubiquitous offering in San Francisco bakeries and restaurants.
Sourdough breads are made with naturally fermented starters. One interesting thing about such breads is that the starter is unique to the area it is cultivated in, since it consists of local yeasts and bacteria. As a result, sourdough breads from around the world taste radically different, depending on the origin of the starter, even when they are prepared in the same way. The starters of some regions of the world have become famous for their flavor and performance, and San Francisco's is one such example.
The history of San Francisco sourdough began with the Gold Rush, when numerous enterprising bakers started opening bakeries to cater to hungry gold miners. Many of these bakeries produced sourdough bread in the French and Italian tradition, using starter they grew themselves, and San Francisco's sourdoughs proved to be unusually delicious, with a tender texture and complex flavor which started to make the city famous. In addition to the starter, San Francisco sourdough bread includes flour, salt, and water, with some bakeries adding a small amount of oil as well.
In the 20th century, four bakeries emerged as the kings of San Francisco sourdough bread: Colombo, Parisian, Toscano, and the Boudin Bakery. Today, the first three are united under a banner company, although they actively compete with each other, and Boudin Bakery remains independent. Several of these bakeries claim to be using starters which date to the late 1800s, refreshing their starter every morning to make a new batch of bread in the traditional way. These bakeries ship San Francisco sourdough bread all over Northern California in addition to providing bread for San Francisco.
The famous starter for San Francisco sourdough bread includes a number of special yeasts and bacteria. One yeast, Candida humilis, appears to be unique to San Francisco, as is the dominant Lactobacillus bacterium, Lactobacillus sanfrancisco. The unique combination of local yeasts and bacteria is also influenced by the precise location in the city where the starter is cultured, which explains why home cooks in San Francisco can produce a range of sourdoughs when they make their bread from scratch.