Pizza Hack: Is Copper Better Than the Baking Steel?

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If a steel makes a better baking surface than stone, would copper be even better? [Photographs: J. Kenji Lopez-Alt]

I've been singing the praises of the Baking Steel—a solid steel slab designed for baking pizzas—ever since it came out a couple years ago. It totally revolutionized the way I and many other folks make pizza at home, producing pizzas with better hole structure and a crisper bottom crust than anything you could get off of a traditional pizza stone. It's also virtually indestructible, meaning you'll never have to replace a cracked stone again.

The reason it works so well? It all has to do with the thermal properties of steel. The goal when baking a pizza is to get heat energy transferred into that stretched raw dough very, very quickly. This is what causes the rapid expansion of interior bubbles giving you a bubbly, soft crumb (that's "oven spring" for you baking nerds), and it's what creates the coveted leopard-spots of crisp char on the underbelly.

Steel has significantly higher thermal conductivity than stone (it transfers heat from one place to another faster), as well as a higher volumetric heat capacity (a quarter inch slab of steel will hold much more heat energy than a quarter inch slab of stone), which is what makes it such a great baking surface.

But a couple months back I got a message from longtime Serious Eater Ratbuddy with an intriguing idea. We all know that copper is the king of cookware with even better conductivity than steel, right? So what if we were to bake pizzas on a slab of solid copper?

Well, Ratbuddy didn't just come up with the idea, he actually went ahead and got a couple of 1/4-inch food-grade copper slabs manufactured. I managed to get my hands on one of them for some testing.

Conductivity vs. Capacity

Before we get to the testing, let's take a look at the numbers. Here's a table with the volumetric heat capacity and conductivity of stone, steel, and copper.

Material Volumetric Heat Capacity (j/cm3) Thermal Conductivity (W/m.K)
Stone 0.48 1.5
Steel 3.94 54.0
Copper 3.49 401.0

If we look at the first column, it's pretty clear that both metals are leaps and bounds beyond the stone, with steel coming out slightly on top. Over on the thermal conductivity side, stone is again at the lowest rung. Steel is significantly better, but copper outstrips both by a mile, with nearly eight times the conductivity of steel.

The question is, which of these factors is more important? Will the higher conductivity of copper beat out the higher heat capacity of steel?

Only one way to find out.

The Test

For this testing, I baked a half dozen pizzas on each surface using my Basic New York-Style Pizza Dough recipe.* In both cases, I preheated the oven to 550°F for 30 minutes, then baked the pizzas a few inches from the broiler element with the broiler switched on. Here are the results.

*I also took the opportunity to do some testing for an upcoming kale pizza recipe. Stay tuned for that!

The Steel

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As usual, my Baking Steel produced enviable results with plenty of big, poofy bubbles in the crust. This is the kind of internal structure I always aim for in my pizza.

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The underbelly was also quite nice, with a super-crisp, thin layer of crunchiness laced with streaks of dark brown sections and a sprinkling of near-black charred spots.

The Copper

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That glistening copper sure looks pretty gorgeous in there, doesn't it? I popped on pie after pie to compare the results.

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Uh oh. Surprisingly, the copper slab actually produced pizzas with slightly less oven spring than the steel did. Take a look at the hole structure in that crust edge and compare it to the one produced by the steel above. See what I mean?

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Similarly, the underbelly was not quite as deeply charred as the one cooked on the steel.

Conclusion

As it turns out, conductivity is not the overriding factor when selecting the ideal material for baking on. Heat capacity seems to actually have a much greater effect on the outcome. There's also another factor that I didn't measure or account for: radiation. Dark steel may simply be emitting more heat energy in the form of radiation than the bright, shiny copper, which means that even the bits of pizza dough that aren't in direct contact with the material would be getting a good influx of energy.

In retrospect, this is not actually all that surprising. In fact, pan manufacturers have know this for years. It's the reason why copper cookware is almost always lined with steel. If you take a look at the Copper Core pans from All-Clad, for example, they're made by sandwiching a sheet of copper in between two sheets of steel, giving the pan both great thermal heat capacity, and great conductivity.

Conductivity is especially important in a stovetop setting where energy is coming from a burner—a pretty uneven source of heat. In an oven, however, the air is heated much more evenly, so conductivity is not quite as essential.

So are we barking up the completely wrong culinary tree here? I wouldn't rule it out quite yet. If we were to make a dual-ply baking surface with a copper base topped with a layer of steel, perhaps we'd finally have the king of pizza baking surfaces.

Given the price of copper it'd probably still cost a few hundred bucks a pop, but a guy can dream, right?

For now, my recommendation still stands: the Baking Steel is the best pizza baking surface on the market right now. And for those of you asking about the reversible Baking Steel griddle, it's slated to hit the market in early 2015. Stay tuned!