Levains (also called starters) are simply cultivated, captured wild yeast spores. To create a levain, flour and water are mixed together and left to rest for a substantial period of time. Yeast spores collect on the mixture and begin to multiply. The starter is fed and watered regularly to cultivate the yeast and prevent the spores from dying. Once a large amount of starter has been created, a measured amount can be mixed into a dough to provide leavening while the remainder of the starter continues to be fed and watered for future use. Some starters are very, very old and have been handed down from generation to generation. It is this naturally fermented mix that produces breads with a very distinct, but desirable sour taste and aroma.
