One thing I have noticed is that many of the TAs in Birmingham (some 10 miles apart) serve identical onion salad. Sliced white onion, tomato, cucumber, and a little bit of dried mint. It always struck me as a bit odd. It stays fresh for ages, a hint of sweetness, and never bitter. Always perfect; a little too perfect. Turns out (a chef told me recently) they buy it ready-made, in large bags, and just get one out of the fridge each night. The chef said TA's are all about speed. It also goes in a lot of different curry dishes and is part of the taste, apparently. But the BIR aroma? I don't know. My money's on the oil, and an 8 kW burner.
Rob