Conduction
This is the exchange of thermal energy through direct contact between a heating element and the food. Different materials result in different heating times and temperatures. Please refer to the article Equipment and Gear: Common Materials of Cookware for a complete breakdown of materials that directly affect conduction.
Pan-frying or saut�ing are common forms of conduction. The pan heats up and, through direct contact with the food, cooks the food. Fat or oil used in the frying provides uniform contact with heat, lubrication to prevent sticking, and some flavor of its own. Oddly enough, cooking in oil is considered a dry technique because the oil acts more like a cooking material than anything else. The moisture in the food will still be contained because it will not mix with the oil surrounding it.
Convection
Whereas in conduction heat is transferred through direct contact, in convection, heat is transferred by the movement of molecules in either gas or liquid. The fast moving molecules of the convection medium collide with the slower molecules in the food and heat them up. Baking and roasting are common forms of convection cooking. The heating elements within the oven heat the air and that comes in contact with the food. Boiling and steaming are also forms of convection with water or steam acting as the convection fluid. In deep-frying, the oil envelops the food, like a fluid pan that completely encases the food and heats the surface evenly.
Convection relies much on the density of the fluid. Liquid convection, either through boiling, steaming, or deep frying, is a much more effective transfer of heat than gas convection. This is why boiling a potato is much faster than baking. The denser the fluid, the more often the molecules collide with the food and the fast the food heats up. Therefore in convection methods involving air such as baking, the temperatures must be much higher than in liquid convection. This is why you can stick your hand into a 500�F oven without burning yourself but you cannot stick your hand into a pot of boiling water at only 212�F.
Radiation
While conduction and convection are heating methods through molecule to molecule contact, radiation is the transfer of heat through waves of pure energy. Most of the heating energy comes from the infrared radiation below visible light. When you hold your hand near glowing coals or a stovetop burner, the heat you feel is infrared. Technically, everything emits thermal radiation including you and me, and so every cooking method has an element of radiation.
Grilling and broiling, the former with heat below the food, and the latter with heat above, are two methods of radiation cooking. Of course there is convection from the air in between the heat source and the food and conduction from the grate, but the heat is primarily radiated.
Microwaves are below infrared waves on the spectrum and so carry much less energy. Infrared waves have enough energy to heat up almost all types of molecules, but microwaves tend to only heat up polar molecules such as water, sugar, and fats. Foods containing water are heated by these microwaves which penetrate about an inch into the food's surface. The interior of the food is still heating by conduction of the heat from the surface into the interior.
Answers
February 22, 2010
Conduction
This is the exchange of thermal energy through direct contact between a heating element and the food. Different materials result in different heating times and temperatures. Please refer to the article Equipment and Gear: Common Materials of Cookware for a complete breakdown of materials that directly affect conduction.
Pan-frying or saut�ing are common forms of conduction. The pan heats up and, through direct contact with the food, cooks the food. Fat or oil used in the frying provides uniform contact with heat, lubrication to prevent sticking, and some flavor of its own. Oddly enough, cooking in oil is considered a dry technique because the oil acts more like a cooking material than anything else. The moisture in the food will still be contained because it will not mix with the oil surrounding it.
Convection
Whereas in conduction heat is transferred through direct contact, in convection, heat is transferred by the movement of molecules in either gas or liquid. The fast moving molecules of the convection medium collide with the slower molecules in the food and heat them up. Baking and roasting are common forms of convection cooking. The heating elements within the oven heat the air and that comes in contact with the food. Boiling and steaming are also forms of convection with water or steam acting as the convection fluid. In deep-frying, the oil envelops the food, like a fluid pan that completely encases the food and heats the surface evenly.
Convection relies much on the density of the fluid. Liquid convection, either through boiling, steaming, or deep frying, is a much more effective transfer of heat than gas convection. This is why boiling a potato is much faster than baking. The denser the fluid, the more often the molecules collide with the food and the fast the food heats up. Therefore in convection methods involving air such as baking, the temperatures must be much higher than in liquid convection. This is why you can stick your hand into a 500�F oven without burning yourself but you cannot stick your hand into a pot of boiling water at only 212�F.
Radiation
While conduction and convection are heating methods through molecule to molecule contact, radiation is the transfer of heat through waves of pure energy. Most of the heating energy comes from the infrared radiation below visible light. When you hold your hand near glowing coals or a stovetop burner, the heat you feel is infrared. Technically, everything emits thermal radiation including you and me, and so every cooking method has an element of radiation.
Grilling and broiling, the former with heat below the food, and the latter with heat above, are two methods of radiation cooking. Of course there is convection from the air in between the heat source and the food and conduction from the grate, but the heat is primarily radiated.
Microwaves are below infrared waves on the spectrum and so carry much less energy. Infrared waves have enough energy to heat up almost all types of molecules, but microwaves tend to only heat up polar molecules such as water, sugar, and fats. Foods containing water are heated by these microwaves which penetrate about an inch into the food's surface. The interior of the food is still heating by conduction of the heat from the surface into the interior.
March 24, 2012
We recently purchased a conduction stove and no matter what we try the food sticks to the surface of the pan. Are there any tips on how to avoid this?