New info from the Kushi site (hope you dont mind me posting this pete  

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Curry aroma:  Pete Sheldon, undisclosed location, UKPeter Sheldon has asked a question about curry aroma.
It?s not strictly about the book, but as we?re still waiting for it to published, we thought we?d post some thoughts about his question as a one-off.
He says whenever he goes past a takeaway or a restaurant, there is sometimes a very strong smell - spicy and very strong.  The smell seems to get into all the curries ? but doesn?t appear to be of anything in particular.  It?s not the curry base sauce, garlic or ginger paste - or spicy dishes cooking in the tandoor.  What is it? 
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It?s an interesting question, and one which will continue to provoke much discussion as we reckon it doesn?t have a definitive answer ? but a rather mundane one.  As far as we can work out, it really is nothing more complicated that a combination, (over a very long time) of various curry dishes cooked and served in the restaurant.  Simple as that.  This aroma seems to permeate everything, and because it?s pungent, appears to linger for a long time.  This is especially evident if you go into an Indian or Balti restaurant which has, say, been closed for a couple of weeks holiday.  Even though no food has been cooked there for a while, the aroma which has permeated everything inside (including furniture, walls etc.) is still very much there.  All it takes is more heat and cooking to really bring it back to life.  Conversely, it can take some time for that aroma to fully ?make its presence felt? in a brand new restaurant where such food has never been cooked before.
Trying to recreate this characteristic smell at home proves almost impossible, unless you?re cooking a wide variety and huge quantity of dishes on a more or less daily basis.  (Note from co-author Andy:  I?ve visited Mr. Haydor?s house on many occasions, and even though many curries are cooked there, the volume is nowhere near what you?d find made in a curry house ? and therefore it doesn?t smell like his restaurant!). 
Another more ?scientific? theory (from an aromatherapy expert, who?s asked not to be identified) is that when you cook the dishes at home, the resultant smell may be very similar to that of a restaurant.  But, because you?ve been cooking all the individual ingredients together, your mind ?knows ? what the smell is a combination of, and concentrates on that rather than the resulting mix.  When people arrive for your Balti dinner parties, many will comment that your house smells exactly like a restaurant, as they get the same instant ?hit? of aroma that you get when you walk into a curry house ? whereas your senses are filled with all the constituent stages of cooking.  It?s only a thought, and if we come across any other theories about how you can instantly create this at home, we?ll post it here.  We?d like to thank Pete for his comments, and hope that?s been of some help.