Early Baking: Oven Spring

When the bread first enters the oven, heat moves into the bottom of the dough from the oven floor or pan, and into the top from the oven ceiling and the hot air. If steam is present, it provides an initial blast of heat by condensing onto the cold dough surface. Heat then moves from the surface through the dough by two means: slow conduction through the viscous gluten-starch matrix, and much more rapid steam movement through the network of gas bubbles. The better leavened the dough, the faster steam can move through it, and so the faster the loaf cooks.