Dough, whether for pizza or for bread, baked on a stone surface such as the floor of a brick oven or one of those flat stoneware oven accessories called pizza stones, really does come out crisper and browner than if it were baked on a metal baking sheet or pan.
If the oven walls are also stone or brick, so much the better. Early bakers had to build their ovens out of available natural materials such as stone and bricks made of clay. Today we bake our bread in “improved,” technologically sophisticated ovens made of steel. And ironically, they don’t do nearly as good a job.
Brick and stone have two properties that make them work so well: high heat capacity and high emissivity.
Heat capacity is a technical term meaning, well, the capacity to hold heat. If a substance has a high heat capacity, it can absorb a lot of heat without its temperature going up very much. That resistance to having its temperature changed cuts both ways: during heating and during cooling. Once the substance has had its temperature raised, it doesn’t want to cool down any more than it wanted to heat up, so it retains its temperature for a relatively long time.
Stone and brick have higher heat capacities than metals. For the same thickness, an oven floor made of fire clay has twice the heat capacity of iron and two and a half times the heat capacity of copper. So once heated to the desired temperature (and that may take a long ti me), a clay floor holds its heat well, staying uniformly at that temperature and resisting temperature changes, such as when relatively cold dough is placed on it.
Note also that the larger the mass of a material, the higher its capacity to hold heat, just as a bigger pitcher can hold more water. That’s why massive brick ovens with thick floors and walls have always been valued for their baking prowess. On a smaller scale, that’s also why a heavy frying pan “holds its heat” (that is, stays at a constant temperature) better than a thin one.
Brick, clay, and stone have a second, even more powerful advantage over metallic oven materials: their vastly superior emissivities.
Infrared (loosely called “heat”) radiation in a hot oven is absorbed by the molecules of the materials it strikes, which then re-emit much of the radiation almost instantly. In some substances, notably metals, most of the absorbed radiation is dissipated before it can be reemitted. Only a fraction of the absorbed radiation (16 percent in the case of a stainless-steel oven wall) is returned promptly to its environment: the air in the oven. (In techie talk, the emissivity of a stainless-steel surface is 0.16.) The rest of its heat stays in the oven wall and is wasted, as far as the food is concerned, except that it can slowly and inefficiently work its way back into the air.
Even at the same temperature, then, stone emits more infrared radiation than metal does. And because infrared radiation doesn’t penetrate beyond the surfaces of materials, more infrared radiation striking the dough results in better browning and crisping of its surface.
So whether you’re reheating a delivered pizza, making one from scratch, or baking a free-form loaf of bread, place it on a preheated pizza stone. If the stone is unglazed and therefore porous, it will have the additional advantage of absorbing the steam emitted from the bottom surface of the dough, keeping it dry for even more effective crisping.
