For purposes of this discussion, we define a sourdough as a dough leavened by a sourdough starter. A sourdough starter is a dough or batter that contains wild yeasts and bacteria, has a noticeable acidity as a result of fermentation by these organisms, and is used to leaven other doughs.
Sourdough starter is also called a natural sour or natural starter. Before commercially prepared yeast was available, bread was started by mixing flour and water and letting this mixture stand until wild yeasts began to ferment it. This starter was then used to leaven bread. A portion of the starter was saved, mixed with more flour and water, and set aside to leaven the next day’s bread. This process is still used today.
