Pizza Ovens: Radiant Thermal Powerhouses

Traditional Neapolitan-style pizza has a blistered, slightly charred, crisp crust with a moist and chewy crumb and simple toppings. The secret to this flatbread’s characteristic texture is in the cooking method. Wood-fired brick ovens have an atmosphere of intense heat for rapid cooking, with a stone surface that promotes a crisp crust. Knowing how to properly track and manage the oven’s temperature is critical to a successful pizza cook.

What is Radiant Heat?

Radiated thermal energy is transferred due to the emission of electromagnetic waves. Think of the sun’s intense heat on a summer day, or warming your hands near a fireplace—that’s radiant heat.

Simply put, the heat from the fire inside the oven heats the bricks of the oven’s dome and floor, and once those materials have absorbed all the heat they can, it begins radiating that heat inside the oven.

Radiant methods of heat transfer impart energy in the form of electromagnetic energy, typically microwaves or infrared radiation. The warmth you feel when sunlight hits your skin is radiant heat. —Cooking for Geeks, Jeff Potter

Radiant Heat Dominates A Brick Oven

The intense heat absorbed into the pizza oven bricks from the fire is radiated back down from the dome, and that is what actually cooks the pizza—not the hot air in the oven or the heat directly from the fire itself. Because the radiated electromagnetic waves are coming from so many different angles of the dome walls and floor of the oven, hot spots can exist on the oven’s cooking surface.

➤ How high are these high temperatures?

By trying various temperatures, I’ve found 600°F (315°C) to be the lower limit for getting a crispy, flavorful crust. At 700°F (370°C), the crust becomes noticeably better. And at 950°F (510°C) it takes 45 seconds to cook a pizza. —Cooking For Geeks, Jeff Potter

Let’s took a look inside a pizza oven to observe how the heat energy transfers. The unique physical properties of brick and concrete are what make pizza ovens the thermal powerhouses that they are. These properties include:

Thermal Mass:

Thermal mass is the ability to absorb, store, and release heat energy. The brick, stone, and concrete these ovens are made of have great thermal mass which stores thermal energy to keep the heat in the oven consistent.

Efficient Emissivity:

All objects radiate thermal energy, but do so at different levels of efficiency. Brick and concrete are able to radiate thermal energy with nearly 100% efficiency. Strong emitters are also strong absorbers.

Emissivity is a measure of the efficiency in which a surface emits thermal energy. An emissivity value of 1 is a perfect emitter, with a value of 0 being a perfect thermal mirror (reflector). Think of the difference between cast iron skillets and aluminum ones. The cast iron retains and emits heat very efficiently, while the aluminum one deflects its heat quickly. (Read more about the thermal properties of cast iron in our post Grill-Worthy Burgers Indoors.) 

During the heat-up phase, the heat radiating from the fire in the center of the pizza oven is absorbed by the dome and floor of the oven. The high thermal mass of the brick oven absorbs the heat energy like a sponge. Completely saturating the brick can take several hours depending on how thick the dome is and how dense the bricks are. But once the bricks are heated, they are able to store and release that heat over a long period of time. (Our pizza oven was still at 500°F [260°C] two days later, long after the fire had gone out.)

Infrared Thermometers for Surface Temperatures

With all this talk of high temperatures, what is the best way to measure the heat? The pizza comes into direct contact with the oven floor, and its surface temperature needs to be accurately measured. Infrared (IR) thermometers (On Sale Now!) only measure surface temperatures, not internal temperatures.

➤ Emissivity and Accuracy: The accuracy of an IR thermometer’s reading depends on the emissivity of the surface being measured. We’ve already alluded to the fact that brick and concrete have an emissivity value of almost 1 (nearly 100% emissive efficiency). This means infrared thermometers take highly accurate readings of this material.

➤ Readings from a Distance:

The Hi Temp Industrial IR w/Circle Laser, or IR IND, is perfect for taking readings of high heat environments like a pizza oven. The radiated heat of the oven is so intense that you can’t hold you hand near the oven for very long without getting burned.

➤ Optic Range:

The IR IND features a 30:1 distance to target ratio. That means you could stand 30 feet away from your target and still only be measuring a surface about one foot in diameter or, more likely, standing 5 feet away and measuring a surface about 2 inches in diameter. This narrow optic focus make the IR IND ideal for measuring hot spots on a pizza oven floor from a distance—far enough away to stay cool.

➤ Locate Hot Spots:

The IR IND also features a full circle laser that clearly defines the surface area you are measuring, so you can easily see temperature gradients across the entire oven floor to identify hot spots.

When to Spot-Check Temperatures

➤ Carbon Burn-Off:

While the oven is heating it reaches a landmark stage of carbon burn-off. At this stage the soot collected on the dome from the fire clears away. When you see this visual cue, it’s time to check some temperatures.

Using an infrared thermometer like the IR IND, check the temperature of the top and middle of the dome, and the oven floor. Temperatures in the range of 700-900°F (370-482°C) are ideal, and will vary depending on your particular oven.

➤ Temperature Equilibration:

As the bricks reach their maximum heat energy absorption, the difference between the temperature readings from the top of the dome to the oven floor will become smaller as the entire oven equilibrates to one temperature.

This is the point where the bricks really begin to emit heat energy, and the oven becomes a powerhouse of radiant heat. Radiated energy is the dominant form of heat transfer at such powerfully high temperatures, perfect for generating that unique blend of crispiness and chewy crumb you find in the best pizzas.

Look for a narrow range of temperature gradients across the entire oven to signal when it is time to move your fire to the side, clean your oven floor and start making pizzas.

Monitoring Your Oven During the Cook

The total amount of energy radiated by a hot object is proportional to the fourth power of the absolute temperature, so that a coal or metal rod at 2,000°F (1,093°C) is radiating more than 40 times as much energy as the equivalent area of oven wall at 500°F (260°C). —On Food and Cooking, Harold McGee

➤ Fire Maintenance:

Throughout the cook the fire must be managed to maintain the optimal temperature range in the oven. At such high temperatures, a small increase or decrease in the fire’s strength can cause exponentially changes the radiated heat inside the oven.

There are actually mathematical formulas that predict the radiant temperature of pizza ovens and other high heat cooking environments. All of them involve exponents, meaning that small increases in energy inputs (in this case, the fire) can have big impacts on the radiant heat of the oven.

Spot-check surface temperatures frequently and manage your fire to keep the radiant temperature range of the oven stones between 800-950°F (426-510°C).

The Cook

Once the oven is ready to go it’s time to cook. Thin pizzas made from doughs with high hydration (70-75% [try Basic Neapolitan Pizza Dough from Serious Eats]) will cook best—and in only 90-120 seconds!

1. Shape and stretch 8 oz (227 g) of dough
2. Place on flour-dusted pizza peel
3. Add sauce and toppings (use San Marzano tomatoes, fresh mozzarella, and fresh basil for a traditional margherita style pizza)
4. Load pizza onto the oven floor
5. Rotate to allow for even cooking
6. Remove from the oven when the pizza has the level of browning and char that you prefer
7. Slice, and enjoy!

Unlike convection ovens or stove-tops that cook through conduction, pizza ovens and other high heat cooking environments cook through radiant heat. A pizza oven’s efficient heat is due to the particular thermal mass and emissivity of the oven materials. The dome shape helps reflect the radiant heat towards the oven floor.

Pizza in your home oven

Of course, statistically speaking, you don’t have a wood-fired brick oven. You just have your home oven. What can you do to make the best pizza possible for you? For one thing, you can try grilling your pizza. But that still doesn’t help everyone. Perhaps the best option is to use a pizza stone and crank the heat on your oven. Most ovens only go up to about 525°F (274°C), not as hot as the brick oven, but you can still get some good browning and bubbles on your pizza at that temp.

To mimic the brick oven as closely as possible, preheat it well in advance of your baking. You need time for the pizza stone to come completely up to temperature. When you think it’s time to bake, point your IR thermometer (careful with the emissivity setting!) at the pizza stone. The heavy thermal mass of the stone will take longer to heat than the air in your oven, so it won’t do to have the oven alert you when it is “preheated.” An IR thermometer pointed directly at the stone, however, will tell you when it’s time to cook.

Conclusion

Controlling the temperature inside such a high heat environment is tricky and can take practice to master. But infrared thermometers (On Sale Now!) make the job much easier. IR guns like the IR IND are perfect for taking accurate readings of your oven. They can help you know when your oven is ready and when to add or subtract wood from your fire to maintain the proper temperature zones that lead to pizza perfection.

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Products Used:

Resources:

Cooking for Geeks, Jeff Potter

The Pizza Lab: Bringing Neapolitan Pizza Home, Serious Eats

On Food and Cooking, Harold McGee