Heat Transfer in Cooking: Conduction, Convection, and Radiation Explained

Pick up a piece of cold cast iron. Your fingers tell you it’s cold through direct molecular contact. Now hover your hand over a hot pan without touching it. You feel warmth rising. Those are two completely different physical processes, and your kitchen uses all three of them, often at the same time.

The Three Modes of Heat Transfer

Conduction happens when two objects are in direct physical contact and heat flows from the hotter one to the cooler one. At the molecular level, fast-moving atoms in the hot pan collide with slower atoms in the food, transferring kinetic energy. Metals are great conductors. Food is not. Most food is mostly water, which conducts heat about 25 times worse than steel.

This matters because it explains something cooks discover fast: the outside of a thick steak can reach searing temperatures while the center is still cold. Heat has to conduct inward, molecule by molecule, through tissue that’s a poor conductor. That temperature gradient is the whole point of cooking technique.

Convection is heat transfer through a moving fluid, where “fluid” means any liquid or gas. When you put food in boiling water, hot water molecules carry energy to the food surface continuously. The same happens in an oven, but far less efficiently, because air has a much lower heat capacity than water. A 350°F oven and a 350°F pot of water feel nothing alike. The water will cook food dramatically faster because it transfers far more energy per second.

Radiation is what happens when energy travels as electromagnetic waves through empty space. Infrared radiation doesn’t need any matter to move through. Your broiler emits these waves, and the food surface absorbs them and converts that energy to heat. Radiation explains why the top of a lasagna can brown while the bottom stays pale, and why you can toast bread without the bread touching anything hot.

Why Most Cooking Uses All Three at Once

A cast iron pan on a gas burner looks simple but involves all three modes. The flame heats the pan by convection (hot combustion gases moving over metal) and radiation (the flame emits infrared). The pan then conducts heat into the food touching it. Meanwhile, the sides of the pan radiate heat toward the food too. Even the fat in the pan convects heat, flowing around the food surface and carrying thermal energy along with it.

A good analogy: think of heat as money, and cooking methods as different payment systems. Conduction is like handing cash directly, fast but only at the point of contact. Convection is like a bank transfer, it spreads to wherever the fluid goes. Radiation is like a wire transfer that moves at the speed of light and doesn’t need an intermediary at all.

Stovetop vs. Oven: A Practical Consequence

The stovetop is mostly conduction. The oven is mostly radiation and convection. That’s why they produce such different results.

Pan searing a steak on a hot cast iron surface transfers enormous amounts of heat at every point of contact. The Maillard reaction starts almost immediately, because you’re hitting 300°F+ at the interface within seconds. The Maillard reaction needs surface temperatures above about 280°F, and direct conduction from a 500°F pan gets there fast.

Put that same steak in a 400°F oven and the browning is slower. Air is a poor conductor. The steak is surrounded by hot air, but air molecules transfer heat lazily. The inside of the steak may reach your target temperature before the surface develops a proper crust.

That’s why the reverse-sear and the sear-then-oven sequence both work well. The oven handles the interior gently and evenly with low-intensity heat. The pan handles the surface with high-intensity direct contact.

Why Water-Based Convection Is So Efficient

Water’s heat capacity is roughly 4 times that of most oils and about 1000 times that of air. When you submerge food in water at 212°F, the rate of heat delivery to the food surface is dramatically higher than in a 212°F oven. That’s why boiling cooks food so much faster than air-roasting at the same temperature.

Steam is interesting because it adds a phase-change bonus. When steam condenses on cooler food, it releases its latent heat of vaporization, about 540 calories per gram. That energy transfer is far greater than what dry air delivers. This is why steam burns are so dangerous, and also why a steam injection in a bread oven dramatically speeds crust formation.

Sous vide pushes water convection to its logical extreme. The food sits in a precisely controlled water bath, where the high thermal mass of water keeps temperatures stable within a fraction of a degree. Because water convects heat so effectively, the food eventually reaches equilibrium with the bath. You can’t overcook past the bath temperature. Read more in sous vide science.

Deep Frying: The Conduction-Convection Hybrid

Hot oil works differently than hot water. Oil can reach temperatures well above 212°F without boiling, which unlocks the Maillard reaction and rapid surface browning that water can’t achieve. When food enters the oil, the surface moisture flashes to steam almost immediately. That steam creates an outward pressure that temporarily slows oil absorption and creates the characteristic fry bubble.

The oil conducts and convects heat to the food surface at very high temperature. You get the efficiency of liquid convection plus the high temperatures that only non-water liquids can sustain. That’s a combination no oven can match for crust development speed.

Radiation and Browning

Broiling puts food close to an intense infrared source. The surface absorbs radiation and heats almost instantly. This is why broiling is so effective for thin items: the surface browns before the interior overcooks.

Thicker items don’t work as well under a broiler because the radiation only penetrates the surface. The interior has to heat by conduction, which is slow. A thick pork chop under a broiler will have a charred surface and a cool center if you’re not careful.

Microwave radiation is different from infrared. Microwave ovens emit radiation at a frequency that water molecules absorb directly, vibrating them and generating heat throughout the food rather than just at the surface. That’s why microwaved food heats through quickly but doesn’t brown. There’s no high-temperature surface event.

The Practical Takeaway

Understanding which mode dominates lets you troubleshoot. Food not browning? You probably need more conduction (hotter pan, direct contact) or more radiation (broiler position, higher oven temp). Food browning on the outside but raw inside? Too much surface heat relative to interior conduction. The fix is lower, slower heat, or more time.

Every cooking method is just a different strategy for delivering energy. Once you see them clearly, you stop following recipes blindly and start understanding why each step works.