Why a wood-fired, earthen oven?
Modern cookbooks make bread-baking seem complicated and difficult—which it is not. Building and baking in a woodfired earthen oven restores the simplicity of bread by returning you to essentials: earth, water, air, and fire.
Plants transform the energy of the sun into woody material, fire transforms wood into energy, and the massive walls of an earthen oven absorb and concentrate that energy as heat. After a couple of hours, the oven is hot enough that you can remove the fire and bake bread. The hot, dense mud radiates its stored heat at a steady rate (like the sun!)
Radiant heat is fundamental to our very existence—from it we have photosynthesis and weather, food and shelter, and sunny days on the beach, not to mention wheat and bread. The architect Christopher Alexander says that humans have a biologically built-in human preference for radiant heat—his answer to why people prefer an open fireplace to an open heating vent. Perhaps that’s another reason why bread is better baked in a wood-fired oven . . .
Radiation is one of three ways that heat can be transferred from oven to bread: the other two are convection and conduction. Convection is the reason why warm air rises—heated air molecules move faster—the faster they move, the farther apart they get and the fewer of them there are in a given amount of space. Fewer molecules have less weight, making hot air lighter than cold air; thus, hot air rises. Convection works in any gas or liquid, but it doesn’t work in solid materials, like brick or metal. So heat doesn’t always rise, or at least, not exclusively. In a solid material, heat moves in all directions, by a method called conduction. Conduction is how a hot frying pan cooks an egg—direct contact with hot metal transfers heat very quickly to the egg, which cooks much faster than it would if it was only in contact with hot air.
Modern ovens depend primarily on convection, so it's not the oven that does the cooking; instead, the air carries the heat to your bread, and the bread cooks. Even if a modern oven has no hot or cold spots, baking more than two loaves requires careful arrangement so the air can carry equal amounts of heat to every loaf. Fancy, so-called "convection" ovens try to improve the situation with a fan that hurries the hot air around. Special baking pans or stones can help improve your bread, but they are poor substitutes for the original oven, which was made of earth.
An earthen oven bakes your bread using all three kinds of heat transfer: radiant heat from the hot walls; conducted heat from hot bricks through the bottom of the loaf, and convected heat from hot, steamy air swirling inside the sealed oven. With all this heat from every direction, many loaves cook as easily as one. In addition, the different kinds of heat working together improve what is called "oven spring"—the irregular air holes and high loaf that happen when a vigorous batch of yeasty dough gives a final surge of activity in response to a hot floor and hot, steamy air. In addition, superheated steam caramelizes the sugars in the outside layer of dough, producing a lovely, crisp, substantial crust.
Building and baking with a wood-fired earthen oven not only makes wonderful bread, it can also teach you things you'll never learn with a modern oven, bread machine, or book. Instead of turning switches, you will come to know earth, air, fire and water, and you will come to know the life they give to grain and yeast and bread, as well as the life they give to us. Books can explain why, but the best way to really understand is to do it yourself. "You got to go there to know there."
Earthen ovens are better for baking because they provide an even source of all three kinds of heat:
1. Radiant heat, from hot, massive walls
2. Conducted heat, from direct contact with a hot brick floor
3. Convected heat, from hot, moving (and steam-charged) air.
Earthen Building, or what is "cob," anyway?
Earth is the most common, and perhaps the most versatile building material on the planet. Mixed with sand and straw, a clay subsoil will become very hard and durable; indeed, it was the first, natural "concrete." In the Americas, this material is called "adobe," from an Arabic word, al-toba, meaning "the brick." Invading Moors brought the word to Spain from North Africa, where the ancient tradition of mud building continues today. In Britain, the continuing tradition of earthen building is called cob, from an old English word meaning "lump." The Brits skipped the step of forming bricks, and made their walls by packing wet blobs of mud on top of each other, letting them dry, and carving them smooth. Five-hundred-year-old cob houses are common in Devon, England, where they are recognized on historic registers, and command high prices when sold.
Protected by roof and foundation from direct rain and snow, earthen buildings hold up very well, even in damp, windy Devon. I built a mud studio in the temperate rainforest of the Oregon coast range, and it is warmer and drier than my wooden cabin—not to mention that it's impervious to fire, and the bugs that eat wood can’t stomach it.
Building a mud oven is like building a mud house, on a smaller scale. The dome shape is basic in nature, common to beehives, bird's nests, caves, cliff dwellings, igloos, huts, and the Houston Astrodome—strong, self-supporting, easy to build and heat.