HEAT TRANSFER
Heat is an exchange of thermal energy. Its molecules have absorbed energy, when a substance gets hot, which causes the molecules to vibrate rapidly, expand and bounce off one another. As the molecules move, they collide with nearby molecules, causing a exchange of thermal energy. The faster the molecules within a substance move, the higher its temperature. This is true no matter the substance is water, air, a sirloin steak or an aluminum pot.
Thermal energy may be exchanged to foods through convection, radiation or conduction. Heat then travels via foods by conduction. Only thermal is transferred cold is simply the absence of thermal, so cold cannot be transferred from one substance to another.
Convection
Convection refers to the exchange of thermal via a fluid, which may be gas or liquid.
…show more content…
Water is a better conductor of heat than air. This explains why a potato cooks much faster in boiling water than in an oven, and why you cannot place your hand in boiling water at a temperature of 212 F (100 C), but can place your hand, at least very briefly, into a 400 F (200 C) oven. Generally, metals are good conductors, and gases and liquids are poor conductors.
Conduction is a relatively slow method of heat transfer because there must be physical contact to transfer energy from one molecule to adjacent molecules. Consider what happens when a metal spoon is placed in a pot of simmering soup. At first the spoon handle remains cool. Gradually, however, heat travels up the handle, making it warmer and warmer, until it becomes too hot to touch.
Conduction is important in all cooking methods because it is responsible for the movement of heat from the surface of a food to its interior. As the molecules near the food’s exterior gather energy, they move more and more rapidly. As they move, they conduct heat to the molecules nearby, thus transferring heat through the food (from the exterior of the item to the