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01. Conduction

Heat makes molecules move faster. The faster they move, the more likely it is that they will bump into an adjacent molecule and transfer heat from one molecule to the other. This straightforward interchange of energy is called conduction. It is the basic way that heat moves from the fire to the surface of the grill grate, through the grill grate, and, finally, into a piece of food.

Although conduction is at play in all areas of the grilling process, the way heat moves through a metal grate is different than how it moves through a slab of meat, for instance. Metals are particularly good heat conductors because, even though most of their molecules are tightly bound, they contain electrons that jump easily from one atom to another. This mobility of electrons moves heat quickly through metal grilling equipment. But meat and other grilled ingredients don’t heat through as efficiently.

Before a steak even touches the grill, the grill grate should be thoroughly heated, which ensures that the surface of the meat gets a blast of energy at the onset of cooking. That’s why most grilled steak recipes direct you to preheat the grill. For direct grilling, a hot grill grate is necessary to force heat deeply into the meat as quickly as possible; once the heat moves from the highly conductive metal grate into a less conductive steak, the heat transference slows down dramatically. The surface of grilling meat continues to receive the bulk of the available heat energy throughout the cooking process, passing it along very gradually, which allows us to produce a thick crust on the surface of a steak while keeping the interior moist and rare.

The amount of heat coming from the fire itself has little effect on how fast that heat transfers through the meat; a hotter fire simply makes the surface crustier. So the more well-done you like your meat, the lower the temperature must be to ensure that the center cooks through without scorching the surface. Likewise, large, thick roasts need to be grilled away from direct heat to give heat traveling through the meat enough time to reach deep into the center.

02. Convection

While conduction moves heat to food through the metal grill grate (and throughout the food itself), convection moves heat around food. As the fire heats air inside a closed grill, the molecules in the air move faster. Moving molecules take up more space than still ones, which makes the hot molecules rise. Air currents develop, circulating hot air toward the top of the grill, which forces cooler air down toward the fire, where it is heated, causing it to rise, and so on. Convection is not a primary method of heat transference in grilling (especially with no grill lid), but it does account for some of the cooking that takes place in indirect grilling, in which food does not come into direct contact with a hot grill grate or a radiating flame.

03. Radiant Heat

Radiation is harder to understand than conduction or convection, because this type of heat never touches the food, yet it is the principal form of heat transference in grilling. The best way to grasp the process of radiant heat is to think of the sun. The sun’s heat radiates through space to the earth, warming the planet. Along the way, it doesn’t heat up the void of outer space, as it would if convection were taking place, and there are no metal wires traveling from the sun to the earth, conducting the heat to us. In radiation, energy is passed from one atom to another in the form of pure energy, until it comes in contact with a convecting fluid (like our atmosphere, in the case of solar energy) or a conducting solid (like a hamburger, in the case of grilling), where its energy manifests itself as heat.

Radiant heat is invisible (a good reason why it’s hard to visualize). It is one of many forms of radiant energy that are used extensively in everyday life: Radio waves, TV waves, microwaves, visible light, and X-rays are all forms of radiant energy with different strengths. Their relative strengths, called frequencies, are measured on the electromagnetic