Every cooking method is a way of getting heat into food. There are only three ways heat moves, and most methods use all three.
Key idea
Conduction: heat passes by direct contact, from burner to pan to food, and from the outside of the food to its center. Convection: a moving fluid (air, water, oil, steam) carries heat; a convection oven's fan speeds it up. Radiation: heat travels as infrared light from a glowing source, as in a broiler, a grill or a salamander.
| Method | Main way heat arrives |
|---|---|
| Sautéing | Conduction from the pan |
| Deep-frying | Convection in hot oil |
| Roasting | Convection of hot air, plus radiation from the oven walls |
| Broiling | Radiation from above |
| Boiling and poaching | Convection in water |
| Steaming | Steam condensing on the food (it gives up a lot of heat as it turns back to water) |
Why it works
Inside food, heat moves only by conduction, which is slow. That's why thick food cooks slowly and why a very hot oven can burn the outside of a roast before the center is done. Thin pieces, or lower heat for big pieces, give the inside time to catch up.
Worked example: Which way?
A salamander browns the top of a crème brûlée.
- The heat comes from a glowing element above, through the air, as infrared light.
Answer: Radiation.
Common mistake
Turning a convection oven to the same temperature a recipe gives for a still oven. Many recipes and oven makers suggest about 25°F lower, or a shorter time, because moving air cooks faster.
Practice at home
- Put two identical potatoes in a 400°F oven: one whole, one cut in half. Check both with a skewer every 10 minutes. Which is done first, and why?
The science behind it
- Conduction, convection and radiation: the physics of heat transfer
- Rate of heat conduction: why thickness matters so much