Oven Spring Is Steam and Trapped Gas Expanding
That final burst of rise a loaf gets in the first several minutes of baking — oven spring — comes from trapped carbon dioxide and alcohol from fermentation rapidly expanding as they heat, plus water in the dough flashing into steam, before the crust sets and locks the structure in place. A hot oven (and steam injected early, which keeps the crust flexible longer) maximizes it; scoring the dough's surface gives that expanding gas a controlled place to escape instead of tearing the loaf open randomly.
Sources & methodology: These tips draw on established food-science references —
Harold McGee's food-science writing, America's Test Kitchen /
Cook's Illustrated testing, Serious Eats'
technique reporting, USDA food safety guidance,
and peer-reviewed food-safety research (including UC Davis
cutting-board studies) — not reworded recipe-blog consensus.