Any of several species of plant grown for its acrid seeds and leaves which are called mustard greens. There are two major types of mustard seed: white (or yellow) and brown (Asian), A third species, the black mustard seed, has been replaced for most purposes by the brown species because the latter can be grown and harvested more economically. Black mustard is a round hard seed, varying in color from dark brown to black, smaller and much more pungent than the white. White mustard seeds (round hard beige or straw colored seeds) are much larger than the brown variety, but a lot less pungent. Its light outer skin is removed before sale. With its milder flavour and good preservative qualities, it is most commonly used in ballpark mustard and in pickling. White and brown seeds are blended to make English mustard. Brown mustard seeds are similar in size to the black variety and vary in color from light to dark brown and are more pungent than the white, less than the black. Brown mustard seeds are used for pickling and as a seasoning and are the main ingredient in European and Chinese mustards. Powdered mustard is simply finely ground mustard seed. Originally mustard was called Sinapis. Some claim that during Roman times the word Sinapis started to be replaced by words such as Mustum, Mustarum, and Mustardum as new wine, or "Must" was mixed with mustard seeds to make a paste. More recent theories come from France. In one, the Duke of Burgundy gave the town of Dijon a coat of arms in 1382 with the motto MOULT ME TARDE. As the story goes, the motto was adopted by the town’s mustard-makers, who eventually shortened it into Moul-tarde (to burn much). Another story has it that the motto was given the citizens of Dijon by King Charles VI. In this version, the motto "MOULT ME TARDE" meant "Off to Battle."
Seeds can be stored up to a year in a dry, dark place; and powdered mustard for about six months.