In order for food to be cooked, heat must be transferred from a heat source (such as a gas flame or an electric element) to and through the food.
Heat is transferred in three ways:
Conduction - Heat conducted by fire, hot plate, griddle plate, pot/pan, or grill.
Convection - Heat conducted by hot air, dry and wet steam, water, and oil, as in a steamer or convection oven.
Radiation - Heat conducted by infrared heat or microwaves, as in a broiler, salamander, or microwave oven.
