Many folks define a basic difference between yeast and sourdough. Simply put, yeast baking relies on active dry yeast as the rising agent. Sourdough, well, sourdough calls for a starter of flour and water, or so they say. Janet Calhoun, retired Mansfield City School teacher, begs to differ. “Saying sourdough is not yeast is like saying Granny Smiths are not apples because they look and taste different than Macintosh apples,” she said. Granted, sourdough starter begins as nothing more than flour and water. When left on a counter, yeast spores in the room temperature air pay the starter a visit. As Calhoun explains, it is those yeast spores that bring about the fermentation of the flour and water to develop a product with its own rising strategy.