Bread is a fermented food, provided that it is made with a sourdough starter.  A sourdough starter is a yeast and bacterium culture that ferments flour and water. This fermentation process gives bread its distinctive taste and texture.  While some commercial bakeries add yeast to their doughs, authentic sourdough bread is made without any added yeast.  Instead, the naturally occurring yeasts in the flour are used to leaven the dough.