What Kind of Bread Molds the Fastest?

How fast bread molds depends on its ‘water activity.’ Pure water obviously has an activity of 1.0 and 0 is completely dry. Water is not bound to the bread, so bread typically has a water activity of .95 and mold stops growing when the water activity drops below .81. Basically, the speed of mold is more determined by how it’s stored than the type of bread. Dryer is better so toss your loaf in the fridge or toaster and you’re good to go.