Since the flour’s normal endowment of sugars is enough to feed yeast cells for only a short period of time, flour manufacturers have long supplemented the ground wheat with malted wheat or barley: grains that have been allowed to sprout and develop the enzymes that break down starch to sugars. Because malt flours give a dark cast to flours and doughs, and because their activity is somewhat variable, manufacturers are increasingly replacing them with enzymes extracted and purified from microscopic molds (“fungal amylase”).