The baker’s controlled fermentation rest, during which shaped dough matures in warm, humid air before baking. Amylases clip starch into fermentable sugars that yeast converts to carbon dioxide and alcohol; the gas inflates the myriad tiny bubbles created during mixing, and the loaf swells, often roughly tripling in volume. Judging the endpoint is a craft skill: under-proofed dough bakes dense, over-proofed dough collapses. Commercial provers hold temperature and humidity precisely, and the stage is also called proving in British usage.