A type of sourdough bread made famous in San Francisco. It is one of the most well known varieties of American bread outside of the United States. Sourdough was a popular variety with the pioneers during the 1849 Gold Rush in California. San Francisco sourdough is made with a combination of white and whole-wheat flour and it is usually baked into a round loaf with a crosshatched pattern (similar to tic-tac-toe) slashed across the top. The special tangy flavor of San Francisco sourdough is due to the preparation of the bread using a starter dough as the leavening agent rather than with the use of commercial yeast. San Francisco sourdough is an excellent sandwich bread and is a great accompaniment to many soups and salads.