By Harold McGee
A general method for incorporating yeast into bread dough that maximizes the effective fermentation time and flavor production is the use of pre-ferments or starters, portions of already fermenting dough or batter that are added to the new mass of flour and water. The starter may be a piece of dough saved from the previous batch, or a stiff dough or runny batter made up with a small amount of fresh yeast and allowed to ferment for some hours, or a culture of “wild” yeasts and bacteria obtained without any commercial yeast at all. This last is called a “sourdough” starter because it includes large numbers of acid-forming bacteria. Starters go by many names— French poolish, Italian biga, Belgian desem, English sponge—and develop different qualities that depend on ingredient proportions, fermentation times and temperatures, and other details of their making. Sourdough breads are described.