[Ming the Merciless]

http://www.amazingribs.com/BBQ_buyer...as_grills.html

charcoal makes more smoke than gas, although, when lit completely, when fed the proper amount of oxygen, good charcoal produces very little visible smoke. In fact, the best tasting smoke is called blue smoke and is barely visible. If you are using gas, the smoke from combustion is rarely visible, but there are still flavorful combustion gases given off.

A lot of the smoke happens as drippings from the food hit the hot surfaces below. Meat drippings are mostly water, fat, and protein, plus whatever you have added, such as marinade barbecue sauce. When they hit the heat source they vaporize and some of that vapor condenses on the meat. Most gas grills cover the flame jets with metal plates, lava rock, or ceramic rocks that absorb the heat and radiate it, but the food is not exposed directly to flame. Drippings may hit these radiant surfaces where they are vaporized, making smoke and steam, much like charcoal. Some new gas grills have "infrared" burners which are superheated surfaces that are very close to the meat and more vapors get back to the meat with these burners.

There is also a difference in the flavor imparted by the volatile by-products given off by the burning of the charcoal or the gas. When propane combusts it makes more steam than charcoal, and that may help keep meat moist giving gas an advantage for some meats. Some cooks think the steam can be a disadvantage for some meats, hampering chicken skin from getting crisp for example. Charcoal produces more tiny particulates that land on the surface of the meat. But, smoke is not likely to significantly change the flavor of food that is cooked quickly such as hot dogs, burgers, or skinny steaks.

chimney for starting barbecueThere is one other flavor difference of note. If you use self-igniting charcoal or charcoal fluid to start a charcoal fire, there can be an unpleasant petrochemical smell during ignition and it can get into the food. Yuk. For this reason you should use a charcoal chimney, a torch, or an electric charcoal starter.