Our usual approach to creating steam in a home oven doesn't produce steam for very long. We’ve come up with a more effective approach.
Professional bread ovens boast pressurized valves for injecting steam into the oven at the beginning of baking for three important reasons. For starters, a moist environment transfers heat more rapidly than dry heat does, allowing the gases inside the loaf to rapidly expand in the first few minutes of baking, ensuring maximum volume. At the same time, steam prevents the bread’s exterior from drying out too quickly, which would create a rigid structure that limits rise. Finally, moisture converts the exterior starches into a thin coating of gel that eventually results in the glossy, crackly crust that is a hallmark of a great artisanal loaf.
Our usual approach to creating steam in a home oven is to pour boiling water into a preheated loaf pan placed on the oven’s bottom rack, but the water doesn’t continue to boil for very long. Inspired by the superheated stones used to generate steam in Swedish saunas, we’ve come up with a more effective approach: using lava rocks. These irregularly shaped rocks (available at many hardware stores for use in gas grills) have a lot of surface area for absorbing and retaining heat, maximizing the amount of steam produced when boiling water is introduced.