Steel: The Ultimate Grill Hack

I was reading Scott Heimendinger of Seattle Food Geek fame and ran across this superb article.  I have not hacked my home grill, but after reading this article I am giving it a second thought.   The following excerpts caught my attention.

Physics Interlude!

Mass, like a pizza stone, or the thick floor of a pizza oven, or in this case, 25-lb steel plates, act like a heat battery, storing up heat energy.  I was first turned on to the idea of using steel instead of ceramic brick by Modernist Cuisine, who recommend the technique not only for grills but for household ovens as well.  So, why are steel plates better than a pizza stone?  A few reasons:

  1. Steel is much denser than ceramic materials.  A typical pizza stone has a a density of 0.0625 lbs. per cubic inch.  The steel plates I’m using have a density of 0.329 lbs. per cubic inch – about 5 times as dense.  That means that for the same volume of material, I can store much more energy in steel than brick.
  2. Steel has a much lower specific heat than brick.  This means that it takes less energy to heat a steel block than a brick of equal mass.  So, the steel will heat up faster in the oven.
  3. Steel has a much higher thermal conductivity than brick.  Thermal conductivity measures how quickly heat moves through a material, or between materials via conduction. This means that the heat can move from the steel plate to the pizza crust faster than it could if I were using a ceramic material.

All of these factors are summed up in one convenient measure, known as thermal diffusivity.  And, it turns out that the thermal diffusivity of 304 steel (the grade I’m using) is about ten times greater than the thermal diffusivity of brick.  [I don’t have precise numbers for the ceramic composition of pizza stones specifically, but it will be similar in magnitude.  Some types of steel, like high-carbon steel, have more than 20 times the thermal diffusivity of brick.]

Do ceramic pizza stones produce good-looking, great tasting pizzas?  Yes, absolutely.  But according to physics, they necessarily do so more slowly than steel.  One of my pizza criteria is a crunchy crust that will support its own weight when held from one end.  I’ve found great success in achieving this texture with a steel cooking surface.  The other advantage to steel, of course, is that it will last nearly forever.  I don’t have to worry about dropping and shattering it, I can use it as a griddle and scrape it clean, and if I need to build an impromptu blast shield, I’m all set.

Thermal diffusivity tells us how fast the heat flows through materials.  Materials such as copper and steel conduct heat faster than materials such as wood and brick.  In our case, the Baking Steel is made from carbon steel (TD 11.72) which has more than 20 times the thermal diffusivity of brick(TD .52).   When we were designing our Baking Steel, the technical terms were not discussed, in fact I'm just learning about these characteristics.  Here is what we do know, steel gets hot, very hot, conducts evenly and is not going to break.  Preheat your Baking Steel in the oven for 45 minutes and slap some dough down with a peel and watch it cook beautifully.    With the Baking Steel inside, you will now have a great tool to help make superior pizza.  Whether or not you want to hack your grill, I think Scott is on to something.  Just be careful.

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