Moisture in the oven during the first phase of baking that keeps the crust flexible, allowing maximum oven spring before the crust sets.
Professional bread ovens inject steam directly. Home bakers use a Dutch oven (which traps the dough's own moisture), a pan of boiling water on a lower rack, or ice cubes thrown onto a preheated tray. Steam is critical for the first 15-20 minutes. After that, you want a dry oven to crisp the crust. If your bread isn't getting good oven spring or the crust is pale and dull, insufficient steam is the most likely culprit.
