A long fermentation gives the yeast a chance to produce its own flavors and convert the starch to sugar. By refrigerating the dough overnight, you can make excellent 100% whole wheat bread. Yeasts perform differently at low temperatures. The dough is mixed the day before and refrigerated. The acids and enzymes produced by the yeast at lower temperatures temper the harshness of the whole wheat and develop wonderfully complex bread flavors. It’s no more work than other recipes; you just mix the dough the day before.