Whole mustard seeds are important in South Asian cuisine where generous quantities are added to the oil or butter in which vegetables are to be fried or which will used to begin the process of making a curry. Since mirosinase, the enzyme that produces the bitingly hot, sinus-opening impact of mustard, is only activated by water, this technique produces a delicious, slightly piquant, nutty flavour rather than heat. Mustard seeds explode in hot oil - hold a lid above the pan to prevent them from flying all over the kitchen!