Escape of Water Vapor and Other Gases

Throughout the baking process, some of the water turns to steam and escapes into the air. If this takes place before the proteins coagulate, it contributes to leavening. In addition to steam, carbon dioxide and other gases escape as well. In yeast products, alcohol produced by the fermentation process is one of these gases.

Another result of the loss of moisture is the beginning of crust formation. As moisture is lost from the surface, the surface becomes harder. The crust begins to form even before browning starts. Baking breads with steam injected into the oven slows crust formation by delaying the drying of the surface. Delaying crust formation allows the bread to continue rising.