A sourdough starter is a mixture of flour and water that attracts wild yeast found in the air, on the surface of flour and even your hands.
The starter becomes a food source for the yeast.
By giving the starter fresh flour and water once a day, these yeast began to multiply, producing more and more yeast within the starter. When enough of these yeast are present, the starter is strong enough to make bread rise.
Once mature, a portion of active sourdough starter is added to sourdough bread dough for baking. This is commonly referred to as naturally leavened bread, as there is no commercial yeast in a sourdough starter.
