When you set a pot on the stove or slide a tray into the oven, you’re engaging in a complex and often inefficient dance of energy transfer. Heat is at the heart of cooking, but how it moves—and how much of it reaches your food—is more complicated than it seems. The science of heat in cooking reveals surprising inefficiencies, hidden variables, and even a bit of math that can change the way you think about your kitchen.
There are three main ways heat moves: conduction, convection, and radiation.
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Conduction: Heat by Contact
Conduction is the transfer of energy through direct contact. It’s how a frying pan sears a steak or a burner heats the bottom of a pot. The heat travels from particle to particle, working its way from the outer layers toward the center of the food. But not all materials conduct heat equally. That’s why oven mitts protect your hands—they’re made of materials with low thermal conductivity. Metals, on the other hand, are excellent conductors. However, conductivity is just one part of the equation.
To really understand how cookware conducts heat, you also need to think about specific heat capacity (how much energy a material can store) and density (how heavy it is). The combination of these three properties—conductivity, heat capacity, and density—determines a material’s thermal diffusivity, or how quickly it transmits heat.
That’s why aluminum pans heat quickly (low density, high specific heat capacity), while cast iron pans heat slowly but retain and distribute heat evenly (high density, low specific heat capacity). Copper cookware strikes a balance and is prized for its high diffusivity.
Cooks often obsess over whether their pans are copper, aluminum, or stainless steel—but the thickness of the cookware also matters. A pan that’s too thin may heat quickly, but it can also transmit the burner’s hot and cold spots directly to the food. A thicker base gives the heat time to spread sideways as well as upward, smoothing out those inconsistencies.
The theoretically perfect pan responds quickly to changes in burner temperature but retains enough heat to cook steadily. It’s a tricky balance, and not one manufacturers always make easy to understand. We go into further detail about how to pick an affordable but workable pan in this blog.
While cookware performance matters, food itself is what slows things down. The cells and water content in food create a structure that resists the flow of heat. That’s why it takes time for heat to reach the center of a thick steak or a loaf of bread. Geometry plays a big role here: not just how big something is, but how thick it is relative to its other dimensions.
Here’s where it gets interesting: if you double the thickness of a food item, it doesn’t just take twice as long to cook—it takes four times as long. That’s because conduction follows a square law relationship. Triple the thickness, and you’ll need nine times the cooking time.
This rule works best for flat items like steaks or fillets. Once you get into cube-shaped foods or cylinders like sausages, the math gets murky and simulations are needed. When in doubt, go slow and use a thermometer.
EXAMPLE: Sautéing and Conduction
Sautéing is a great example of conduction, considering a great sauté depends on fast, even heat conduction. The goal is to cook food quickly—getting heat from the pan to the surface of each piece and then into the center before anything burns. Because heat moves more slowly inside food than across its surface, small, uniformly cut pieces are essential. They not only cook faster but also brown more evenly, which is critical for flavor and texture.
Oil plays a key role in this process. Even in a nonstick pan, food touches the surface in only a few spots, with air gaps insulating the rest. A generous layer of oil fills those gaps and conducts heat far more effectively than air. It also coats the food as you toss it, helping every side get exposed to the pan’s heat. If you don’t use enough oil, the food may stick or cook unevenly—some parts burning while others stay raw.
As food cooks, it releases water. If the pan is overcrowded or the burner too weak, those juices pool, cooling the pan and halting browning. Instead, leave space in the pan, use strong heat, and listen closely. The initial loud sizzle signals good heat conduction and rapid evaporation. As the food dries out, the sizzle softens and rich aromas emerge—your cue to pay attention. A quick toss keeps everything moving through the hot oil, ensuring each piece cooks evenly and absorbs the full benefit of conduction.
Convection: Heat by Transfer
Convection is the transfer of heat through a fluid—in cooking, this means either air or liquid. For example, when food is boiled or simmered in water, convection currents form as hotter water rises and cooler water sinks, circulating heat throughout the pot. The same principle applies in ovens: hot air moves around the food, transferring heat to its surface. Convection can be further enhanced by fans in convection ovens, which create a more even and often faster cooking environment. Convection is particularly effective for increasing the speed of cooking compared to relying on conduction alone.
EXAMPLE: Boiling and Baking
Boiling is an excellent example of convection cooking—where heat is transferred through the movement of a fluid, in this case, water. As water reaches a rolling boil (100 °C / 212 °F at sea level), it churns vigorously, creating a turbulent bath that moves hot liquid around the food. This motion accelerates heat transfer, cooking items like vegetables or eggs quickly and evenly. The energetic bubbling also bursts tiny air pockets in plant tissues, enhancing color and texture—as seen when green beans shift from dull to vivid green. Though often maligned for overcooking, boiling, when used properly, is fast, efficient, and ideal for blanching vegetables and cooking pasta and potatoes.
Baking is a quintessential example of convection cooking through air, where hot air currents inside the oven transfer heat to the food. As a loaf of bread bakes, the oven’s preheated air circulates around the dough, carrying thermal energy to its surface. The surface of the loaf heats up first, undergoing a rapid temperature rise during the settling period. At this stage, the air’s warmth causes moisture at the surface of the dough to evaporate, drying it out while also increasing the humidity inside the oven.
Convection doesn’t stop at the surface. As evaporation continues, internal moisture migrates outward to replenish what’s lost, propelled by diffusion and capillary action. Meanwhile, the hot, dry air steadily penetrates the loaf, gradually cooking its interior and triggering the expansion of gases that give bread its rise. By the time the loaf reaches the falling-rate period, a crisp crust has formed, created by the continued exposure to dry, moving air and the slowing of internal moisture movement. In this way, baking harnesses the power of convection through air—not just to heat food, but to transform its texture, structure, and flavor.
Heat by Electromagnetic Waves
Radiation, by contrast, transfers energy without the need for direct contact or a circulating fluid. It occurs when electromagnetic waves carry energy from a heat source to the food. Every heat source radiates light—but that light isn’t always the visible kind. The wavelengths of light used to cook food are mostly in the microwave and infrared range, longer than the longest wavelengths of visible red light. Broilers, toasters, and even glowing charcoal primarily cook food through radiation, which is also called radiant heat. Both visible and infrared radiation radiates from the heating elements or glowing coals.
Unlike convection or conduction, radiation heats the surface of the food directly, often resulting in faster browning or charring. This kind of energy transfer can be very intense, making it ideal for creating crisp crusts or seared exteriors. Dark food with a dull surface will absorb more of the heat rays hitting it than a light-colored or shiny food—just like how a black shirt gets hotter in the summer sun than a white shirt. And as food darkens, it absorbs more radiant energy, which speeds up the cooking process.
Microwave ovens also use electromagnetic waves called microwaves, which are a type of invisible light that heats food differently than radiation.
EXAMPLE: Broilers and Microwaves
Broiling is a powerful cooking method that relies specifically on infrared radiation to cook food from above. Unlike convection or conduction, which transfer heat through air or direct contact, broiling bathes food in invisible light waves that excite molecules on the surface, rapidly browning and crisping it. This makes broiling ideal for finishing dishes or searing delicate surfaces like fish, gratins, or toast.
To broil effectively, you must locate your oven’s “sweet zone,” the optimal spot where heat is most even and intense—too close and food may burn unevenly, too far and heat may reflect unpredictably. Shiny surfaces reflect radiation and cook slowly at first, while darker ones absorb more energy and can suddenly overcook, so constant attention is essential.
Like grills and broilers, microwave ovens deposit energy and thus heat into food by radiative transfer, but the radiative heating of a microwave works very differently than these other methods do. The microwaves are tuned to a particular frequency that excites vibrations in water molecules—generating heat through friction. Water molecules can receive this kind of transmission because they are polar. Fats and oils are not polar molecules, but they can also be vibrated in other ways using microwaves, so they also become a source of heat generation. Microwave ovens do not heat air, dishes, or the walls of the oven. They heat only water and oil. Dry substances will not heat up at all in a microwave oven.
Microwave ovens are often considered to be second-class tools that aren’t appropriate for “real” cooking. Yet that notion ignores the fact that microwave ovens do an excellent job at many kitchen tasks, such as making beef jerky and frying herbs for garnishes. One issue to keep in mind with microwave ovens is that their wattage—and thus the amount of heat delivered to food—differs from model to model, so some experimentation is required to fine-tune recipes and techniques to the oven you are using.
Understanding how heat works—where it goes, how it’s lost, and how long it takes to travel—can make you a better cook. It’s not just about cranking up the burner. It’s about choosing the right tools, managing heat loss, and knowing how your food will respond.
FURTHER READING
- Modernist Cuisine at Home
- The Household Stove—Modernist Cuisine at Home, p. 36
- Conventional Ovens—Modernist Cuisine at Home, p. 34
- Stoves—Modernist Cuisine at Home, p. 24
- Grills—Modernist Cuisine at Home, p. 44
- Heat in Motion—Modernist Cuisine Vol. 1:277
- When color indicates temperature—and when it doesn’t—Modernist Cuisine Vol. 1:291
- What Makes a Hot Wok Glow?—Modernist Cuisine Vol. 1:287
- Heating Different Materials—Modernist Cuisine Vol. 1:280
- Cooking with Microwaves—Modernist Cuisine at Home, p. 40 / Modernist Cuisine Vol. 1:182
- Cooking with Moist Air—Modernist Cuisine Vol. 2:154–181
- Microwave Myths—Modernist Cuisine Vol. 2:190