A white French bread with a tangy, sour flavor that has been created by using a starter of fermented flour and water, instead of active dry yeast as the leavening agent. Many starter recipes will include yeast to insure the bread dough rises faster, however, the traditional sourdough bread typically did not include yeast, because the starter mixture created the yeast. This bread is considered to be open-crumb bread, containing many varying sized air pockets within the baked dough. Sourdough is a variety of French bread that became prevalent during the gold rush days of the 1800's in and around San Francisco, California. Many recipes differ on ingredients and some will also differ on the texture of the crust, from soft to hard. Today, sourdough is a well-known bread for sandwiches, appetizers, rolls, and other types of foods.