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I don't want petroleum residue on my meat. Gas grills are for wimps who turned their backs on an ancient rite men has shared with every ancestor.
Gas grills are not for me. The wood when burned gives the meat a special taste and aroma. The food is cooked on gas do not. Besides, BBQ is not just food, but also the process of communication. I can not imagine how you can eat the meat roasted over the gas.
Gas grills burn propane which is usually a hydrocarbon mix, but this is still the volatile end of hydrocarbons. That means it's a very pure mix of H and C atoms. I wouldn't worry about "petroleum residue."
I've cooked meat on gas grills and wood fire and took them inside, and people uniformly prefer the wood cooked fire product.
However, many vegetables don't do well with the smoke flavor. (A few do)
Gas grill for me is the same as barbecue cooked in electric barbecue. For me it's not food. Besides, I like to look at the embers. This is one of the weaknesses of man.