Cover the bowl with a plate, towel, or plastic wrap and set it aside to rest at warm room temperature (but not in direct sunlight) for at least 12 hours and preferably about 18 hours. (Ideally, you want the room to be about 72°F. In the dead of winter, when the dough will tend to rise more slowly, as long as 24 hours may be necessary.) ☞ TESTER TIP: You'll know the dough is properly fermented and ready because its surface will be dotted with bubbles. This long, slow fermentation is what yields the bread's rich flavor.