The Importance of Steam for Crust Formation

Numerous factors contribute to achieving an artisan bread crust at home, but one that is arguably the most impactful is the use of steam when baking bread. If you want to achieve a shiny, crisp, and beautifully golden brown crust on your sourdough or yeasted boules and batards, then using steam is absolutely essential.

During baking, bread needs two things– heat and moisture– to achieve a great crust. The oven provides the heat, and the moisture can either come from the loaf itself or be added to the hot oven as the dough bakes. Moisture, in the form of steam, impacts several crust qualities—from volume expansion to crust thickness, crispness, and color.

The Role of Steam in Bread Baking

Steam during the early stages of baking keeps the dough’s surface moist and flexible, delaying crust formation and allowing more time for volume expansion, or oven spring.

During the first 15 minutes of baking, bread dough rapidly expands as the CO2 inside heats up and expands, while the gluten network traps these gasses, causing the dough to rise. Steam is essential for maximizing oven spring, as water vapor condenses on the surface, preventing it from drying too soon. This helps create a thinner crust and a more open crumb, as the dough has more time to expand before the crust sets.

Without enough moisture, the exterior hardens prematurely, restricting expansion and resulting in a smaller, denser loaf. Additionally, the condensation creates a cooling effect, allowing more time for enzymes to produce the sugars and amino acids necessary for the Maillard reaction, which occurs later and gives the crust its color and flavor.

Steam helps gelatinize the dough's exterior surface, giving it a shiny, crisp crust that shatters when cut open.

In addition to delaying the formation of the crust to allow for expansion, steam facilitates starch gelatinization. When exposed to heat, starch granules in the dough absorb water and begin to swell. Eventually, the granules burst and liquefy, forming a starch gel. As the bread bakes, the surface starch gel dries into a glossy, brittle shell, resulting in the thin, crisp exterior characteristic of artisan loaves.

The Importance of Venting Steam

Baking in a dry oven toward the later part of the baking period contributes to crust color & flavor.

While steam is crucial for a great crust, it's equally important to vent it properly during the later part of the baking. Doing so will allow the crust to dry out and enable the chemical reactions that give the crust its color, flavor, and aroma to occur. The Maillard reaction, which occurs between amino acids and sugars, is a primary contributor to the crust's color, flavor, and aroma. Caramelization, which only involves sugar, also contributes to a lesser degree to the crust's color and flavor. Low water activity and high temperature accelerate these chemical reactions, and excess moisture can inhibit them; therefore, we recommend venting steam later in the baking period. Commercial ovens have built-in steam vents, but with a home oven, you can create a dry environment easily by removing the Baking Shell halfway through the baking time.

How Home Bakers Can Create Steam

While professional bakers use steam-injected bread ovens, home bakers must rely on alternative methods to achieve similar results.

When baking bread in a home oven, there are two main ways to create steam: through a closed bake or an open bake.

In a closed bake, bakers cover the dough with an oven-safe container for the first half of the baking period. Steam comes from the water evaporating from the dough, and the cover traps the steam, creating a self-steaming environment. Traditionally, a heavy cast iron vessel is used, but it can be difficult to manage due to its weight, size, and the risk of burns. An alternative method we prefer is using a lightweight Baking Shell.

The Baking Shell provides everything you need to bake great bread: heat and steam. It heats up incredibly quickly, so there’s no need for long preheating times, and it efficiently traps steam to help create a crisp, golden crust. Its lightweight design makes it much easier to handle than a heavy Dutch oven, reducing the risk of burns when placing or removing dough from the oven. The Baking Shell also cools down quickly, allowing for safe handling and storage soon after baking. The Baking Shell offers all the benefits of a Dutch oven with greater convenience and efficiency.

In an open bake, the bread is not covered, and steam is added directly to the oven chamber. Common techniques include spraying water into the oven, adding ice cubes, or pouring water over hot lava rocks. While these methods can enhance the crust, they are often more trouble than they are worth and produce inconsistent results.

Incorporating steam into your bread-baking routine is key to achieving the ideal texture and crust. Steam plays a crucial role in creating a loaf with excellent oven spring, a crisp crust, and a beautiful golden-brown color. By understanding the importance of steam and learning how to manage it effectively in your home oven, you can take your bread baking to the next level and consistently produce bakery-quality loaves.