The black stuff on the grate isn't smoke. It's old grease and burnt-in residue that heats back up every time you grill, mixes with the meat, and leaves a stale aftertaste that shouldn't be there.
Your wife says it tastes burnt. You know you didn't burn it. Not this time. It's the grate. And you've known it the whole time.
Aaron Franklin, the world's most famous pitmaster, cleans his grate after every cook. Not for hygiene. Because a clean grate gives direct contact with the meat, a more even Maillard reaction, and a sear that actually delivers.
It's technique, not cleaning.