A sourdough porridge bread becomes more slack as it proofs. The surface becomes sticky, making it difficult to unmold, score, and load into the oven.
Linen-lined proofing baskets are preferred for higher hydration doughs like sourdough porridge breads. The linen is cut to size, its edges are folded for durability, and the cloth is stitched onto the banneton. Professionally lined baskets can be found online or in specialty cookware stores. (See photo.)
To make your own, line your banneton with a piece of linen. Thoroughly rub rice flour or a rice flour/whole wheat blend into the linen before placing it in the banneton. Pleat or fold the linen so that it fits as smoothly as possible. Light-weight linen is preferred. Lacking that, any dye-free cloth that’s tightly woven and has a smooth feel can be used. The cloth’s flexibility is more important than what it’s made of. Stiff linen forces the proofing dough into awkward shapes that are difficult to unmold for baking.