Heat in cooking

Heat in Cooking Heat naturally moves from hot surfaces to cooler surfaces. The movement of heat is commonly referred to as heat transfer. There are three methods of heat transfer: conduction, convection, and radiation. Cooking of food usually uses a combination of these methods.  

Conduction

  Conduction transfers the heat using direct contact; food is heated directly in a metal pan, in a liquid, or surrounded by air. Dropping an egg into a pan of boiling water is a good example. The heat from the water is transferred to the egg. As the outside of the egg becomes warm, the heat moves into the center of the egg, continuing inward until the entire egg is heated to the desired temperature. The efficiency of the heat transfer depends on the conductivity of materials in contact with the food. Copper is one of the best conductors of heat. Heat transfers quickly from the heat source into the food through the copper cookware. In contrast, water, stainless steel, and the food itself, are poor conductors of heat.

Convection

Convection heat transfer occurs faster than conduction. Convection occurs by the movement of air, liquid, or steam around the food. For example, as a pan of soup heats up on the stove, heat moves from the bottom of the pan. This movement of hot and cool liquids or gases combines. Stirring the pan redistributes the heat from the bottom of the pan throughout the other ingredients. Convection is the reason frozen foods thaw more quickly when placed under cold running water. Convection can also occur mechanically by means of a fan that circulates the air in an oven. A convection oven can reduce the cooking time by 25 percent over standard ovens. It also increases browning of the food because of the concentrated heat on the surface of the food.

Radiation

Radiation heat transfer occurs when microwave (light waves) or infrared energy (heat waves) are spread into the food. As the microwaves penetrate the food, they bump into molecules of water and fat, causing them to vibrate rapidly. This vibration creates friction, which creates heat that cooks the food. The larger the piece of food, the more unevenly the microwaves penetrate, so microwave cooking has some limitations.