In general, there are two types of karashi, or mustard – Japanese and western. Japanese mustard is made with the seeds of Brassica juncea var. cernua. Oil is extracted from the seeds and then the seeds are dried and ground into fine powder. In powdered form, mustard seed has none of its characteristic pungency. It is only after water is added and the combination with oxygen occurs that the pungency emerges. Karashi made from powder, however, quickly loses its punch, so it should not be mixed up until just before eating and should be covered or otherwise protected from too much air exposure. Western mustard, in contrast, is made from a different variety of mustard plant and offers a flavor that is less intense. Much of the karashi that comes in tubes is western mustard.
Text by Kitchen Nippon