Mustard seed is the small, round, whole seed of several plants in the cabbage family — chiefly yellow or white (Sinapis alba), brown (Brassica juncea) and black (Brassica nigra) — used as a spice in its intact form rather than as the ground, wetted condiment. Toasted whole in hot oil or ghee for an Indian tarka, cracked into a pickling brine, or scattered whole into a corned-beef or sauerkraut crock, the dry seed behaves quite differently from prepared mustard: it is almost odourless and only gently nutty until it is heated or bruised, and its heat is far more restrained because the intact seed keeps its pungency locked away. Popped in fat the seeds turn nutty, faintly bitter and mildly sharp; steeped whole in acid they add a soft, tangy background bite and a pleasant pop between the teeth.