A fermented leavener made from flour, water, sugar, and yeast. Starters were used to leaven bread dough prior to the advent of commercial yeast in the 19th-century. They are still used today, especially to impart a distinctive flavor to a dough(like sourdough). Once it has fermented, remove a portion of a starter to use in a recipe and “feed” the remaining starter with additional flour and water. Those that are maintained regularly and stored under proper refrigeration can be kept indefinitely. See also natural starter, sourdough, and pain au levain.