Charcoal also gives the cook greater control over heat than open flames allow. To understand why, you need to know how a chimney works. Fire is the engine that drives air up a chimney. The flames and hot coals heat the surrounding air, causing it to expand and become more buoyant. The heated air floats to the top of the chimney like a stream of bubbles rising through water. Stoke the fire, and the hot air flows faster; choke the fire, and the flow of hot air slows. The flow of air is called the draft, and it’s directly related to the intensity of the heat from a fire.Just as the draft is controlled by the fire, the fire can also be controlled by the draft. To burn, fire needs oxygen; indeed, it consumes oxygen much more quickly than it does coal. The draft pulls oxygen into the fire: as hot, oxygen-poor air rushes up and away, cooler, oxygen-rich air flows in to replace it. Increase the draft, and you will thus make the fire burn faster and hotter; dampening the draft slows the fire and cools it.Watch a master griller stoke a fire, and you’ll see him rake coals around or perhaps adjust a vent under the grill. Rarely will you see him add more coals. Instead, he’s making the fire hotter by increasing the amount of draft. Slowing the draft, in contrast, starves the fire of oxygen; reduce the draft too much, and the fire will smolder.
If you can control the draft, you can exert masterful control over the heat of a charcoal grill-once you can get the hang of the lag in response