Jerry is right it is mustard oil, the stuff was labelled "for external use only" in the early 90's, thatrs why bir's taste different today.
I think indian cooks still use it only on the sly because they dont want to be closed down for using an ingredient labelled unfit......
Spices of india sell it.
Most indian supermarkets/foodstores stock and sell it, most people in Bangladesh still cook with it.
A recipe told to me by my mate John who cooks and has cooked the best bir balti i have ever tasted....
Take a couple of onions and frey the f**k out of them, until they turn into a brown sludge, then add your spices and mustard oil and fry that together for 5 mins, add this mixture to your stock.
He also says that all this s**t about not browning your onions is b*****s, his words.
I can already imagine the kind of replies this will recieve lol.
And no Im not asking John to post here, he's computer illiterate and wouldn't waste his time, you'll just have to take it as said as i do and put up with it.