How Pizza is Baked: Understanding the Thermodynamics of Pizza Baking

This article focuses on the theoretical principles of how pizza is baked, specifically examining the methods by which heat is transferred during the baking process. While the information presented is primarily theoretical, it is both important and interesting, with practical applications that can enhance your pizza-making. We will explore the thermodynamics of baking pizza, the three methods of heat transfer, their effects on the baking process, and the significance of these factors

How Pizza Is Baked: Introduction

This article takes a primarily theoretical approach, aiming to help you understand the principles behind how pizza, or any other food, is baked or cooked.

Specifically, we will examine the thermodynamics of baking pizza, focusing on the ways heat transfers from various sources to the pizza during the baking process.

While this article is largely theoretical, it provides valuable insights into the practical aspects of baking pizza, providing you with knowledge that can lead to noticeable improvements in your pizza-making skills.

Moreover, the concepts discussed here are essential for understanding the article dedicated to baking pizza in a home oven: How to Bake Pizza in a Home Oven: Everything You Need to Know [A Practical Guide].

The Thermodynamics of Pizza Baking

There are three primary methods of heat transfer, each playing a distinct role in the pizza baking process:

1. Conduction
2. Radiation
3. Convection

Additionally, another important factor in pizza baking is emissivity, which will be discussed later in the article.

Conduction

Conduction is a form of heat transfer where heat moves between objects through direct contact. This process is called conductivity.

During conduction, heat flows from an object with a higher temperature to one with a lower temperature. In simple terms, when two objects touch, heat will transfer from the hotter one to the colder one, until thermal equilibrium is reached.

In pizza baking, conduction is primarily responsible for cooking the bottom of the pizza. The surface on which the pizza sits (such as a baking stone or pan) transfers heat directly to the bottom of the dough, causing it to bake.

Generally, the bottom of the pizza cooks almost exclusively by conduction.

Different materials have varying levels of conductivity, which directly affect the way the pizza’s bottom bakes. To learn more about different baking surfaces and their thermal properties, see the following article: Pizza Steel vs. Stone: The Ultimate Guide to Baking Surfaces [Properties, Differences, Uses & More].

Conduction can also impact the top of the pizza in certain situations. Heat from the baking surface may travel “through” the dough and reach the top, including the sauce and cheese, depending on the dough’s composition.

For example, a very airy dough will limit heat transfer from the bottom to the top. The CO2 produced by yeast creates an “insulating layer” that prevents heat from passing through, concentrating heat at the bottom and not reaching the top. On the other hand, a denser dough allows heat to transfer more efficiently to the top, which can affect the browning of both the top and the bottom.

Based on this principle, the thicker the dough, the more difficult it is for heat to move from the bottom to the top, and vice versa. As a result, thinner pizzas may have a harder time achieving a crispy bottom, as heat passes through the dough without remaining concentrated at the bottom.

Radiation

Radiation, or infrared radiation (IR), is a form of heat transfer that uses electromagnetic waves emitted from a heat source. In this process, heat is “radiated” directly from the source to the surface or object that absorbs it, without the need for an intermediary like liquids, gases, or solid materials.

Under standard baking conditions, radiation is the primary factor responsible for baking the top of the pizza. The heat emitted from the heat source – whether from the heating elements, oven walls, or live fire – has the most significant impact on the baking of the dough, sauce, and toppings (or any part of the pizza exposed to the radiation).

Radiation in baking comes from several sources:

• Electric heating elements
• Oven walls
• Flames
• Coals

In a standard home oven, radiation comes from the top and bottom heating elements, as well as from the oven walls, which absorb heat and emit it back into the oven cavity. When using conventional baking mode (top and bottom heat), radiant energy plays a key role in cooking the food.

In wood-fired ovens, radiation comes from the live fire and, in the case of brick ovens, from the brick walls that absorb and release heat back into the oven.

A critical concept to understand in relation to radiant energy is the inverse square law. This law states that the intensity of radiation decreases quadratically with distance from the source.

For example, if we move 3 meters or inches away from the radiation source, the intensity of the radiation decreases by a factor of 9 (3²); if we move 5 meters away, the intensity decreases by a factor of 25 (5²), and so on. In simpler terms: as we get closer to the radiation source, the amount of heat transferred increases significantly.

This principle is particularly important in baking. For instance, if the pizza is placed 20 cm (8 inches) from the radiation source (whether from live fire or heating elements), it will receive much more heat than if it were placed 30 cm (12 inches) away, and significantly less heat than if it were placed just 10 cm (4 inches) away.

In simple terms, the distance from the heat source significantly impacts how much heat the pizza receives, ultimately affecting the baking process.

Convection

Convection is a form of heat transfer that occurs through the movement of “fluids” – liquids or gases – up and down. In baking, convection refers to the movement of hot air inside the oven cavity. In simpler terms, convection is the process of baking or cooking food using hot air.

Convection results from density differences caused by temperature variations within the fluid (gas or liquid). As the fluid heats up, it becomes less dense and rises, while the colder, denser fluid “sinks” to replace it. This creates a continuous cycle of heat and cold, with the hotter fluid consistently rising to the top.

A classic example of convection is heating water in a pot. The water at the bottom gradually heats up, becoming less dense and rising to the top, where it is replaced by cooler, denser water. This movement continues until temperature equilibrium is reached, resulting in a uniform temperature throughout the pot.

In a standard home oven, as well as in professional deck or wood-fired ovens, natural convection occurs: hot air rises and cold air sinks. However, natural convection is relatively slow, and its impact on baking is much less significant than radiation, often being negligible.

The convection (or “fan-forced”) mode in the oven utilizes “forced” convection. The fan circulates air constantly, creating a continuous flow of hot air in the oven cavity. This way, the heat that bakes the food is due to ‘artificial’ convection, meaning the food is baked primarily by convection (hot air), rather than by radiation from the top and bottom heating elements (which typically do not operate when using convection mode).

Theoretically, using convection helps achieve more even baking, as the hot air circulates evenly around the food. However, the convection function does have its disadvantages, which you can read about in the following article: How to Bake Pizza in a Home Oven: Everything You Need to Know [A Practical Guide] (section ‘Using Convection Mode to Bake Pizza’).

Emissivity

Another factor that plays a role in baking the bottom of the pizza is emissivity.

Emissivity measures a material’s ability to absorb and emit radiation (heat). Its value ranges from 0 to 1:

• A value of 0 means the material neither absorbs nor emits radiation, such as a mirror or reflective surface that completely reflects light or heat.
• A value of 1 means the material absorbs all the radiation it encounters and emits it back to the environment with maximum efficiency.

The more emissive a material is, the more efficiently it converts absorbed energy into thermal radiation, releasing it back into the environment. In simple terms, a more emissive material will emit more radiation (heat) to the surroundings, all other things being equal.

Dark, matte materials are typically more emissive, while shiny or reflective materials have lower emissivity.

For example, aluminum foil, being highly reflective, has an emissivity of 0.03, making it almost a perfect reflector. In contrast, dark metals or pizza stones have an emissivity close to 1.

As we will see later, the emissivity of the baking surface can significantly influence the baking of the pizza’s bottom.

Summary of Heat Transfer Methods: Conduction, Radiation, and Convection

Below is a summary table of the three methods of heat transfer in the context of baking pizza:

The Importance of Balancing Top and Bottom Heat in Pizza Baking

Baking a pizza is primarily about balancing the heat between the top of the pizza – the dough, sauce, cheese, and toppings – and the bottom.

Without this balance, you may end up with a pizza that:

• Too much heat on top: The top is done (crust is browned, cheese is melted, and toppings are cooked), but the bottom is underbaked, remaining white or not browned enough.
• Too much heat on the bottom: The bottom is perfectly browned, but the top is underdone – either the dough is undercooked or the cheese and toppings aren’t sufficiently cooked.

In these cases, continuing to bake the pizza will only worsen the imbalance. If there’s too much heat on top, the pizza may overcook on the top (burning or drying out the dough, cheese, or toppings) before the bottom is fully baked. On the other hand, too much heat on the bottom may leave the top underdone, leading to an overbrowned or even burnt bottom.

Achieving the perfect balance between top and bottom heat is one of the greatest challenges in pizza baking and truly an art form. It requires experience, often through trial and error, to figure out what works best for your specific oven and baking conditions.

Each oven operates differently, and achieving the optimal balance of top and bottom heat depends on several factors:

• Position of the pizza in the oven: The closer the pizza is to the top heating element, the more heat the top of the pizza will receive.
• Baking modes: For example, finishing the bake with the broiler mode can give the top of the pizza a burst of intense heat, resulting in quicker browning.
• Baking surface: A more conductive surface, like a pizza steel, can bake the bottom of the pizza much faster compared to less conductive surfaces.
• Baking in a wood-fired oven: Factors such as the pizza’s position relative to the fire, the temperature of the stone, and the intensity of the flame play a crucial role in achieving the desired results.
• Ovens with separate control of the upper and lower heating elements: Finding the ideal temperature for each heating element.
• Dough formula: Various factors, such as adding sugar or malt powder, and using flours with different enzymatic activity, can influence how quickly the crust browns.

Bottom Heat and Baking the Pizza Bottom

As mentioned, the bottom of the pizza is baked almost entirely through conduction, utilizing heat transferred from direct contact between the baking surface and the pizza base.

The conductivity of the baking surface plays a crucial role in determining how well the bottom of the pizza bakes. Surfaces with higher thermal conductivity transfer heat more efficiently to the pizza base, leading to faster baking and browning.

Earlier, I mentioned emissivity; now, let’s see why this concept is essential when it comes to baking the bottom of the pizza.

The Role of Surface Contact and Emissivity in Baking the Pizza Bottom

During baking, the bottom of the pizza does not come into 100% contact with the baking surface. This occurs because steam forms at the bottom of the pizza, causing the base to “bubble” and temporarily “lift” parts of it above the surface.

The parts of the pizza base that are “lifted off” the surface can no longer be baked via conduction, as they lack direct contact with the baking surface. Instead, these elevated portions are baked through thermal radiation emitted by the surface.

Depending on the composition of the dough and the weight of the toppings (how much the cheese, sauce, and toppings “weigh” the dough down and prevent it from being lifted by the steam), there may be situations where a significant area of the pizza does not come into direct contact with the surface. In such cases, most of the baking of the bottom of the pizza occurs through radiation rather than conduction.

How the surface bakes the areas that do not make direct contact with it depends on the emissivity of the surface. The more emissive the surface, the more radiation it can emit to the bottom of the pizza, effectively baking the elevated parts.

For example, shiny surfaces with low emissivity, like stainless steel (about 0.35 emissivity), may not emit sufficient heat or do so efficiently enough to bake the bottom of the pizza properly. The picture below demonstrates an experiment I conducted of baking a pizza on a stainless steel surface.

Because of this, it’s generally best to avoid shiny or light-colored surfaces for pizza baking, whether it’s a baking surface (like stainless steel) or a pan (such as bare aluminum). Dark, black or opaque surfaces, such as steel, hard-anodized aluminum, or a pizza stone, typically have high emissivity, making them far more effective for evenly baking the pizza base.

Top Heat and Baking the Top of the Pizza

As mentioned, under normal baking conditions and without using convection mode, the top of the pizza is primarily baked through radiation.

In general, the closer the pizza is placed to the radiation source – whether it’s a live fire or heating elements – the more heat its top will receive, accelerating the baking process.

This principle allows for control over the amount of heat directed at the top of the pizza, which in turn gives control over the overall baking process. For instance, toward the end of baking, the pizza can be moved closer to the heat source to accelerate or finish browning. Alternatively, moving the pizza further from the heat source can allow the bottom to bake longer without overexposing the top.