Oil
Cold-pressed oil from brown or yellow mustard seeds, golden to amber, with a sharp, pungent smell.
Caution: Because of its erucic acid content, some mustard oil is labelled for external use only, so for cooking use only oil that is explicitly sold as edible.
Mustard oil is pressed from the seeds of several mustard species and is the everyday cooking and pickling oil of Nepal, Bhutan, northern India and Bangladesh. Raw, it smells and tastes sharp, almost like horseradish or wasabi, and can sting the nose. Heated to just below smoking point it turns milder and nutty, yet keeps a distinct character that defines pickles, vegetables and fish dishes. It is sold in Indian or Pakistani grocery shops, well-stocked Asian shops and by mail order.
Substitute:
Rapeseed or canola oil comes from the same plant family and works as a base; a little mustard powder or freshly ground brown mustard seed brings back some of the heat. The characteristic pungent bite and full aroma, especially in pickles, cannot be matched this way.