Grilling
Part I - Understanding Heat, Grilling, and Barbecue

Food is cooked by heat, obviously. The heat is transferred to the food by one of three ways: conduction, convection, or radiation.

(1) Conduction is the direct transfer of heat by contact with the food, as when an egg cooks because it is in direct contact with a hot frypan or meat browns when in contact with a hot sauté pan.

(2) Convection is the transfer of heat through a medium to the food. The medium may be air, steam, or liquid, such as water or oil. Roasting a chicken in an oven, steaming vegetables in a wok, poaching salmon in water, and deep frying potatoes in peanut oil are all examples of cooking by convection. The convection can be (a) natural or (b) mechanical. Roasting in an oven is natural convection; the hot air naturally rises in the oven, around the chicken, and out the vent. Moving the air in the oven with a fan to accelerate the roasting process is mechanical convection.

(3) Radiation is the heating of food by radiation, that is to say, wave energy. Radiation or wave energy is not heat, but becomes heat when it contacts food. At contact, it increases the motion of the molecules in the food, which is heat. In technical terms, the wave energy becomes kinetic energy in the food.

This might help: light waves from the sun travel in outer space through a vacuum and produce no heat in it. However, if a human was floating through outer space (Space Odyssey 2001) and was hit by light waves, the human would get hot. Why? The light waves would become heat in the human by agitating the molecules in his or her body.
There are two typical kinds of radiation waves used to create heat in food: (a) infrared and (b) microwave. Infrared waves are produced by fire, such as a gas burner, and hot electric elements. When food is close to the heat source, the infrared waves become heat in the food, as when broiling under a red-hot electric element. Microwaves work differently; they increase the motion of water molecules in food, which become heat in the food.  The newest form of radiation to cook food is light waves used in GE's Advantium oven. The oven supposedly cooks food four times faster than a conventional oven, and also produces crisp exteriors, unlike microwave ovens.

It is worth noting that induction, used in induction ranges, is not a transfer of heat. Induction is the emission of magnetic waves that become heat in a pan by creating an electrical current in the pan's metal. That heat is then transferred to the food by conduction, as when an egg fries, or convection, as when water simmers poaching an egg.

Broiling and grilling both use radiation to cook food. The food is constantly exposed to radiation until the cooking is complete. This is because the food is kept close to the heat source, unlike roasting, and the heat is continuous, again unlike roasting during which the oven comes on and off at intervals. Broiling is when the radiant heat comes onto the food from above. Grilling is when the radiant heat contacts the food from below. In both broiling and grilling, air around the food also heats the food, a form of convection cooking, but that is not the primary way the food gets cooked. Radiation hitting only one side of the food is the primary way the food cooks.

A question worth tackling at this time is the difference between grilling and a barbecue. Generally, grilling has a more general meaning: the food is cooked by radiant heat from below. The heat can be from burning wood, coals, an electric element, or gas flames. Barbecue is when the heat source is wood or coals.

"Grilling" obviously comes from the equipment that supports the food: a grill. No mystery there. Barbecue, however, is a more mysterious word. It seems that it entered our language from the Caribbean. It is New World Indian in origin. A barbecue was a raised, wooden framework used for either sleeping on or curing meats. It was called a "barbracot" by the Indians of Guiana and a "barbacoa" by the Indians of Haiti. The Spanish got the word from the Haitians and passed it along to the English. The first known use of the word in English is from 1697; it refers to a sleeping platform. Within thirty years, the word was used to refer to a cooking event: an open-air social gathering which featured the grilling of meat. The reference to a sleeping platform soon became archaic. Today, "barbecue" can refer to (a) the meat being cooked over a fire, (b) the method of cooking over burning wood or coals, (c) the out-door party or picnic, (d) the cooking of meat using a sweet and spicy sauce, a "barbecue" sauce, and (e) a restaurant that uses the method of cooking over an open fire or coals using a barbecue sauce as flavoring.

So there it is: from Indian sleeping platform to outdoor cooking event over a fire using a sweet and spicy sauce for flavoring. No wonder the word "barbecue" is a bit of a mystery.