the starter must be fed 4 to 12 hours prior to being added to dough, by mixing flour and water to the starter. this creates an active leaven, which should grow in size and is ready to use when it is bubbly and floats in water. the leaven is mixed with flour and water to make a final dough of the desired consistency. the starter weight is usually 13% to 25% of the total flour weight, though formulas may vary. the dough is shaped into loaves, left to rise, and then baked. a number of 'no knead' methods are available for sourdough bread. due to the length of time sourdough bread takes to proof, many bakers may refrigerate their loaves prior to baking. this process is known as 'retardation' to slow down the proofing process. this process has the added benefit of developing a richer flavoured bread.