According to King Arthur Baking Company, a culture of bacteria is essential for the formation of sourdough bread. Bacteria, which are found naturally in flour and on almost all kitchen surfaces, feed on a mixture of flour and water – this mixture is called sourdough. Once the yeast settles and begins to eat the starches in the sourdough, it produces bubbles of carbon dioxide (the distinctive flavor of sourdough bread). The exact sourdough flavor depends on the types of wild yeast present and the type of flour used in the sourdough.
Making your own sourdough starter at home is easy. To start, mix 1 cup of flour with ½ cup of warm water in a glass. Cover with a light cloth. King Arthur Baking Company recommends using whole wheat flour, such as pumpernickel or whole wheat, as it is more likely to contain a rich collection of wild yeasts. The mixture should be kept in a warm environment to stimulate growth. After 24 hours, discard ½ of the mixture, add 1 cup of all-purpose flour and pour in ½ cup of warm water. Stir, cover and repeat for the next two to three days. By day five, you should be able to change the mixture every 12 hours.
Sourdough is “ripe” when it doubles in volume every six to eight hours and appears bubbly. Use discarded sourdough for bread recipes, bagels or pancakes.