Add the flour directly into the container with the full batch of room-temperature, batterlike ripe chef. Stir vigorously to add fresh oxygen to the mixture. This will form a stiff consistency more like a stiff dough than a batter. This firm texture is important for ripening levain, because a dense rather than loose levain creates delicious sour bread without an overpowering tangy bite. Scrape down the sides, cover tightly and let stand in a cool to moderate (about 70 degrees) draft-free place for 8 to 10 hours.

The levain should have doubled in volume. The texture will be somewhat light, with many tiny bubbles throughout. Do not let the levain stand for longer than 10 hours, or the yeast will become exhausted and not raise the final dough. Learn more about the levain starter, including how to maintain and nourish the chef, in Dan Lieder's book Bread Alone.