A bread starter, also called a "sponge," is a fermentation starter used in bread baking. It consists of a simple mixture of flour, water, and a leavening agent (typically yeast or yogurt), and is added to bread dough before the kneading and baking process as a substitute for yeast. The advantage of a starter is that it produces chewier bread with a crunchier crust, and helps maintain the freshness of the bread. The starter ingredients are mixed in a container at least three times bigger than the ingredients, to allow plenty of room for the starter to grow. The starter is left sitting at room temperature for anywhere from ten hours to three days before being added to the dough. Starters typically last three to five days, but this time can be extended through refrigeration by providing more water and flour when it is ready to be used.
