On the Record

Physics of pizza

On the Record with Andreas Glatz

Andreas Glatz
Andreas Glatz

DeKALB – Andreas Glatz, professor at Northern Illinois University and scientist at Argonne National Laboratory, met colleague and friend Andrey Varlamov in Rome.

While eating together at a pizzeria, the two physics professors discussed why pizza made in a brick oven at a pizzeria tastes so much better than the pizza made in a metal oven at home.

Glatz usually focuses on dynamical processes in quantum and nano-materials, in particular superconductors and thermo-electric materials. Varlamov focuses on superconductivity, nanophysics and thermo-electric phenomena and is principal investigator of the Institute of Superconductivity, Innovative Materials, and Devices in Italy.

Using their background in physics, Glatz and Varlamov, assisted by food anthropologist Sergio Grasso, wrote a scientific article regarding the physics of baking pizza. The article has been accepted for publication in Physics Education.

Glatz met MidWeek reporter Katrina Milton to discuss his findings about the fundamental thermodynamic principles required to make good pizza.

Milton: How did you first decide to write about the physics of pizza?

Glatz: I’ve worked with Dr. Andrey Varlamov at Argonne National Laboratory for more than 10 years. We both worked on superconductors, have several published articles and a recent review paper together. We are colleagues and friends. During a recent visit to Italy, we were out eating pizza, and started talking. He is also very interested in the physics of the kitchen. After talking, we learned there has been no work published in the English language about the physics of baking pizza, of the science behind what happens when you bake pizza in an oven.

Milton: Tell me a little about the history of pizza.

Glatz: There’s debate on the where the word “pizza” comes from, but it’s often thought that it comes from the Byzantine Greek word “pita.” Pizza was around before Christ. The word “pizza” first appeared around 997 A.D., but that was not pizza as we know it. Pizza as we know it was created not too long ago in the 1800s. In 1889, Raffaele Esposito made a dish to honor the Italian queen with the red, white and green colors of the Italian flag: tomato, mozzarella cheese and basil on dough. That pizza is known as “Pizza Margherita” in Italy today. That was the first pizza as we know it, and it became famous.

Milton: How did you begin your research on the physics of pizza?

Glatz: When we asked the pizzaioli in Rome about how they cook their pizza, we were told that the optimum way to make pizza is for two minutes at 330 degrees Celsius [626 degrees Fahrenheit]. We wanted to know why this temperature, why this time. That’s when we began to think of the thermodynamic processes happening in the oven. We wondered what temperature is needed so that the dough is fully cooked but does not burn.

Milton: Can you explain the science behind the baking of pizza?

Glatz: The heating of pizza can be explained through thermodynamics and physics. If a raw pizza is at room temperature, it is at about 20 degrees Celsius. If that pizza is placed into a 330-degree Celsius brick oven, the temperature at the bottom of the pizza will be about 208 degrees Celsius. Heat will be conducted from the warmer body to the cooler one. The hot oven will be heating the cooler pizza. In addition to this thermal conduction, the pizza is also heated from its top by thermal radiation from the oven walls.

Milton: How is a brick oven different from a metal oven?

Glatz: The main difference for the thermal conduction is the different material of the oven – brick vs. metal. In addition, the brick oven is vaulted, so all surfaces inside the oven are the same temperature and therefore the bricks radiate heat evenly throughout. The different oven materials lead to very different temperatures at the bottom of the pizza, which can be calculated using the thermal diffusion equation. If the metal oven would also be heated at 330 degrees Celsius, the temperature at the bottom of the pizza will be about 300 degrees Celsius, compared to the 208 degrees Celsius in a brick oven. The pizza would burn in a metal oven. We also run into the difficulty of an oven at home not being able to reach 330 degrees Celsius.

Milton: Does the lower heat of metal ovens have a negative effect on pizza?

Glatz: If we heat our ovens at home to a much lower temperature, such that the bottom of the pizza reaches the same 208 degrees Celsius and does not burn, its thermal radiation is quite different. Pizza in a brick oven is continuously heated by an infrared radiation with an intensity of 7.5 kW/m2 per 1 cm2 of pizza. The heating process takes much longer with home ovens. Metal ovens at home are not as hot or powerful, they have an intensity of 3.6 kW/m2 per 1 cm2 of pizza, which is less than half the intensity of a brick oven. Taking into account that the pizza also radiates heat away – the same amount in both ovens – make this ratio even worse. To fix the lower intensity, you can cook the pizza for a longer period of time, but then the dough will overcook and the toppings have too much liquid left. So, you get a not well-balanced product.

Milton: Why is the high temperature important?

Glatz: Physics and the pizzaiolos’ experience tells us that having a constant and even temperature is needed to evaporate sufficient water from the toppings in the same time as the dough needs for cooking. That cannot be achieved at home with a metal oven. We’ve discovered that the temperature of a wood-burning brick stove is ideal for pizza-making. You cannot achieve that temperature at home or the same results with a metal oven without negative consequences.

Milton: What would you recommend for the best at-home pizza?

Glatz: One of the goals in working on this study and writing this article was to help people at home with their pizza-making. We learned that temperature and oven material are very important. If you cannot build a wood-burning brick stove at home in your kitchen or your backyard, visit a restaurant. To help you make a better pizza at home in your metal oven, you can buy a ceramic disc to imitate bricks or a rotating tray, so your pizza is evenly radiated by heat.

Milton: Do pizza toppings change the baking temperature and time needed?

Glatz: Yes, toppings make a difference. In Italy, eggplant is a popular pizza topping, here many people eat pineapple on their pizza. Those toppings have more water in them than more traditional ingredients, so they need to cook longer. Pizzaiolos in Italy lift up the pizza with a wooden peel when the dough is finished baking so the pizza toppings can cook a little longer. Lifting up the pizza allows the toppings to cook without burning the dough.

Milton: Will you research the physics behind other food items?

Glatz: Maybe we will work on other projects. I’m interested in physics behind brewing coffee, in particular in espresso machines. When coffee beans are ground, not all grains are the same size which influences the brewing process. Also, temperature and humidity change the brewing time and pressure for a shot of espresso. There is a lot of interesting physics involved in the brewing process, ranging from granular physics to electrostatic interactions between the coffee grains. Only the optimal grain size will give you the perfect shot.

For more information or to read the article, visit www.arxiv.org/abs/1806.08790.

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