The guys from Tested.com came to Seattle, so I shared with them one of the projects that’s been on my mind lately: making perfect pizzas at home. In a previous post, I discussed my approach to making great pizza dough. But, dough is only one half of the equation. Without a good oven, the best dough in the world still won’t produce quality pizza.
Now, let me first say that there are people who devote their entire lives to pizza ovens – to building them, to studying them, and to understanding how they work. I am not one of those people, and, although I still have a blank space in my yard that I one day hope to fill with an actual pizza oven, my goal here was to produce the best pizzas possible using my CharBroil infrared grill as a starting point. But if you want to send me a pizza oven, I’ll test the shit out of it.
There are two keys to hacking a grill into an effective pizza oven: getting it really goddamned hot, and holding the heat. Getting a grill hot is not so much of a challenge – add enough charcoal and let it burn for long enough, and you’ll have quite an inferno. Add more airflow or additional oxygen, and your fire will burn hotter and faster. But, retaining that high heat when you open the lid or add cold food… well, that requires mass.
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:
- 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.
- 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.
- 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.
To hack your grill into a worthy pizza oven, here’s what you’ll need:
- A grill, preferably one that runs on natural gas, or propane, but has a place to load in charcoal
- Two 1/4” 304 stainless steel plates [either purchased in pre-cut size, or custom cutto fit 2/3 of your grill area]
- 4 5-inch stainless steel pipe nipples, or any other 5” length of stainless to act as a stand for the top plate
- BBQ grill fan, or an electric bellows, or a hair dryer and about 18” of metal tubing to fit
- An aluminum pizza peel
To assemble your pizza oven:
- Place one of the stainless plates in a corner of your grill. The plate should cover 1/3 to 1/2 of the grill area.
- Place two of the stainless steel pipe segments on the two far corners of the plate. Place the other two pipe segments on opposite edges of the plate, about 1/3 of the way back. These pipe segments will hold up the top plate. By pushing them back from the front corners, you allow yourself a little more room to negotiate the pizza with the peel.
- Place the top plate on top of the pipe segments. It should sit firmly – you sure don’t want it crashing down on you during cooking.
- Install your BBQ grill fan or bellows on the opposite side of the grill, above the open grilling area not covered by the steel.
- If your grill has a charcoal tray or basin on the open side, fill it with charcoal. If not, place the charcoal in a roasting pan or metal dish on that side of the grill. Ignite the charcoal, turn on all of the burners and close the lid. Allow the grill 45-60 minutes to preheat thoroughly.
- A few minutes before cooking, start your grill fan or bellows. This will boost the internal temperature of the grill and even out hot and cold spots. A cooking temperature between 800°F and 900°F is ideal.
- Just before cooking, turn the burners below your steel plate down to 75% power. This will help prevent the bottom crust from burning before the top crust is fully cooked. However, I’ve found that the first pizza of the day is usually somewhat sacrificial 🙂
- Slide your pizza onto the bottom steel plate and cook, turning once, for 2-3 minutes or until the cheese is melted and the top crust is golden brown. Keep the grill lid closed as much as possible during cooking to maintain the high temperature.
- Enjoy extraordinary pizza made at home!
I hope you enjoy the pleasure of homemade pizza as much as I have. I’ve probably made 50 or so pizzas this summer, and there is nothing quite as satisfying than pulling a perfect pizza out of the grill and serving it to friends. If you don’t (or can’t) have a grill, this technique works pretty well in a home oven, too. Place one steel plate on the bottom floor of your oven to act as a heat battery. Set the other on the top rack. Preheat your oven for an hour on its highest temperature setting. You’ll need to add a minute or two to the baking time, but the results will be worth it!
You make a good point about the thermal diffusivity of steel! But steel lacks porosity… For some reason I’ve always thought the porosity of ceramic baking stones played a role by absorbing moisture from the dough, thereby allowing for crisper crusts. But perhaps the significantly higher temperature in your setup more than counteracts for this? (i.e. by letting the steam escape side ways) Or could it be that this works well for smaller pizzas, but perhaps not so well for bigger ones? (steam has to traverl further to escape)
Anyway – this little grain of doubt should of course be checked immediately. Can someone please measure the adsorption isotherms for ceramic baking stones ASAP??!!! How much steam can be adsorbed/transported away in a ceramic bakingstone?