Shaping determines whether a loaf rises up or spreads out, and it works by building a tensioned outer skin that resists expansion in every direction except upward. The gas is already in the dough by the time shaping happens. Shaping only decides where it goes. David Anthes, a home baker in Bend, Oregon, treats preshape and final shape as two separate operations with different goals.
Preshaping organizes the dough and gives it a uniform structure before the final shape. The dough is turned out, folded loosely into a round, and left to rest seam side down. The purpose is to establish a smooth outer surface and to let the gluten relax so the final shape can be tightened without tearing. A dough that fights back during shaping was not rested long enough. Anthes gives a preshaped round 20 to 30 minutes on the counter, longer if the dough is strong.
Bench rest length is a judgment call. Too short and the dough resists and tears when the final shape pulls it tight. Too long and it spreads flat, loses the structure the preshape created, and has to be tightened aggressively, which degasses it. The dough is ready when it has relaxed outward but still holds a domed profile rather than a puddle.
Final shaping builds the actual tension. For a boule, the dough is folded from the outside toward the center to create a seam, then flipped and dragged across an unfloured section of the counter. The friction between the dough surface and the bench pulls the skin tight while the seam holds it closed. Flour on the counter defeats this entirely, which is why the dragging surface must be bare. For a batard, the dough is flattened, folded in from the sides, rolled from the top toward the baker, and sealed along the length.
The physics is straightforward. The tensioned skin behaves like a pressurized membrane. As gas expands during proof and in the oven, the skin resists in all directions. Where the baker cuts it, that resistance drops and expansion concentrates. Without tension the gas pushes outward against nothing and the loaf spreads across the stone.
Handling gas is the part that requires restraint. Aggressive shaping expels the large bubbles that produce open crumb and leaves a tight even texture. Timid shaping leaves the skin loose and the loaf flat. The middle approach preserves the larger pockets while still sealing the outside. Anthes finds a lighter hand works when bulk fermentation was complete, and that heavy shaping is usually a baker compensating for a bulk that ran short.
The banneton holds the shape while the loaf proofs. Rice flour is the usual choice for dusting because it lacks gluten and does not hydrate and glue itself to the dough the way wheat flour does. The loaf goes in seam side up so it will be seam side down on the stone, where the seam can seal shut under the loaf rather than blowing open at the side.
Diagnosis after the bake points back to shaping. A loaf that spread wide and baked flat with an even crumb usually had weak tension or an overfermented dough. A loaf that burst along the side rather than at the score had a seam that did not hold. A loaf that is tall and tight all the way through was shaped too aggressively or underfermented. Anthes writes the shape result next to the bulk notes, because the two are rarely independent.