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The Pizza Lab: We Test The New and Improved KettlePizza Grill Insert

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[Photographs: J. Kenji Lopez-Alt]

If you're a pizza geek, no doubt you've seen the KettlePizza insert. It's an after-market device that you add to your weber grill which increases its volume, and provides an opening for inserting and removing pizzas from a stone you place on the grill grate. The food blogs all seem to love the thing. Food Republic has called it a "grilling gamechanger". The Daily What says that it's "life altering". Laughing Squid says it'll turn your kettle grill "into an outdoor oven", while Urban Daddy says it'll "turn an everyday backyard grill into a sublime pizza-making machine".

Sounds like a dream come true, right?

Except for one thing: none of those folks have actually tested the darn thing. Well we did, back in 2010, when it first came out (see the full results here), and were not extremely impressed with the results. We ended up having to use several times more coal than was recommended to get results that were only mildly better than what you can get out of a home oven, and not nearly as good as what you can get by cooking directly on the grill or using the skillet-broiler method in a regular old oven.

Since that early look, the inventor, Al Contarino has jumped into the conversation to let us know that he's come up with a new and improved model that should address many of the problems we had with the old one.

We've also heard from Serious Eats shill commenter Elijahdavid912 that he was able to bake 60-90 second pies on his, calling it "The Answer To All Our Prayers". Those numbers are nowhere near what we managed, even with 3 1/2 times the recommended amount of charcoal being used.

We were all too happy to give the new model another whirl. Here's how it went down.

The Basic Science

Before we jump in, just a quick refresher course on some of the basic science of heat transfer in grilled pizzas:

Frequent Slice readers may know this already, but for those who don't, a Neapolitan pizza cooks via two modes of heat transfer: The bottom of the pizza is cooked by conduction, the direct transfer of energy from the stone to the crust. The top of the pizza is cooked via convection, the transfer of energy via hot air.

Conduction is a much more efficient method of heat transfer, which is why in a professional oven, to cook a pizza properly, the base of the oven need only be around 750°F or so, while the air above must be significantly hotter—in the 1,000°F to 1,200°F range.

The problem with trying to cook a pizza on a stone in a regular kettle grill is that, as many people have pointed out, the stone gets really hot, and it's hard to get the air temp above the pizza hot enough to match it. The bottom of the pizza burns before the top takes on any color. You might think that raising the lid higher and adding an opening would have the opposite of the desired effect, lowering the temperature inside the oven and making the top cook even less efficiently, but this is not the case. The important thing to remember is that moving air cooks a lot more efficiently than still air (think: convection mode in an oven vs. standard mode. The only difference is a fan circulating the air).
So really, the goal when cooking a pizza on the grill should be to get as much hot air circulating over the top surface of the pizza as fast as possible. The main advantage that I see to using the Kettle Pizza insert is that when you get the fire and positioning of the stone right, it creates good convection currents. With the coals banked in the back, hot air rises off the coals toward the domed lid, then gets pulled back down and out the oven door opening. This moving air cooks the top of the pizza a lot faster than the relatively still air inside a completely sealed kettle.

That's the theory. But does it hold up?

The New Model

There are a couple changes that have been made. First, it's now made of a heavier gauge steel and completely unpainted (the old version had a coat of black paint that would burn off at high temperatures). It's also got a cute little "HOT" sign cut into its front, as well as a slightly modified shape to decrease the volume inside the oven.

Al also pointed out that for best results, we should use charcoal briquettes as our base fire and add a few big chunks of hardwood oak to pump up the temperature right before we start cooking the pies.

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It also comes with its own line of accessories now, depending on the model you get. Ours came with a nifty metal peel with a built-in beer bottle opener (how thoughtful!), as well as an American-made round stone for the grill and an aluminum pan, so you have your choice of baking method.

I fired up a full, overflowing chimney of coals, spread'em out in a C-shape (as recommended) in the back of the grill, then put the stone and cover on to preheat. About 15 minutes later, the stone temp was at around 450°F, while the top of the dome was at around 500°F. The air temp inside according to the probe thermometer built into the device was pushing 700°F.

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For the dough, I used my basic Neapolitan Pizza Dough—the kind of pizza dough typically used in the super-hot ovens the PizzaKettle is meant to emulate. Just before stretching and topping the dough, I added a few planks of oak to the fire, quickly replacing the lid to trap the heat.

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By the time I finished stretching and topping the dough, there was a raging inferno going on back there. It buried the needle of the probe thermometer. I'd guess the air temp was around 1,000°F or so, which seems like it should work for Neapolitan pizza.

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The pie went in, and I waited... and waited... and waited... After the first 90 seconds (the amount of time it typically takes to cook a Neapolitan pie start-to-finish), it had shown some decent oven spring and a bit of char on the bottom surface touching the stone, but there was essentially no browning at all on the top surface.

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On the PizzaKettle website, it's suggested that you can "dome" the pies to get more browning on the top; That is, put them on the peel and lift them towards the top of the oven where the air is hotter and the convection currents are faster.

I did this, holding up the pie for several minutes before I finally started to see a hint of browning in the crust.

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The first pie took a total of nearly 7 minutes to cook through, and even then, it was still a bit anemic looking on the top surface.

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Take a look at the cross-section to check out the internal structure:

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Again, decent, but not spectacularly poofy, without the thin-crisp exterior and moist-airy interior you look for in a great pie.

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The undercarriage, on the other hand, looks pretty good to me. Nicely charred and spotty.

As I got ready for round two, I noticed that the temperature had already dropped significantly. Adding a few more chunks of hardwood boosted it again, and I threw in my second pie.

This time, it took even longer to bake, and no amount of doming seemed to help cook the top. I pulled the pie when the bottom was threatening to burn—at around 10 minutes.

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The top of the pie was still completely pale and the crumb was quite dry after that extended baking time.

Why Doesn't It Work?

Unfortunately, the device doesn't produce pizzas as good as what you can get in a real wood-fired stone oven, or even a regular home oven made using the skillet-broiler method. The question is, with the air temp reading off the charts, why doesn't it work? My guess is it all comes down to a lack of radiant heat.

As I mentioned above, pizza cooks via several different modes of heat transfer. Convection is important for the top of the crust, conduction is important for the undercarriage, but radiant heat—that's heat energy transferred directly via electro-magnetic radiation—is also essential for proper browning and charring on the top surface.

With a stone pizza oven, it's not just the air temperature that matters. The amount of energy stored in the stone walls of the oven and re-emitted as infrared radiation is also important. That's why a stone oven needs to be preheated for several hours before you can start baking in it—that energy takes a while to build up. With a kettle grill, you have no material to store the energy. Rather than being collected in thick stone walls, it's conducted straight through. That's all energy that should be going into your pies, but instead is being lost to the air outside.

The Verdict

Our recommendation from our first round of testing still stands: If you want to bake outdoors and get results marginally better than in a regular oven (that is, a regular oven using regular baking methods on a pizza stone), then you might enjoy this product. It's fun, it's pretty, it's well-crafted, and it gets a certain job done.

If, on the other hand, great Neapolitan-style pizza is what you're after—pizza that cooks in a matter of minutes with a charred crust and soft, airy interior—then we recommend using either the skillet-broiler method, or just cooking directly on the grill grates. Both methods will give you superior end results.

Did we miss something here? Have you had a different experience with the KettlePizza? We'd love to hear about it. We've still got the guy set up on our grill, so if you have any suggestions as to how to improve our results, we're more than happy to give it another whirl!

About the author: J. Kenji Lopez-Alt is the Chief Creative Officer of Serious Eats where he likes to explore the science of home cooking in his weekly column The Food Lab. You can follow him at @thefoodlab on Twitter, or at The Food Lab on Facebook.

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