You could be fooled into mistaking fields of white mustard and black mustard plants in full flower, but not by the end products of their seeds. Interestingly, white mustard is more closely related to rocket than it is to black mustard.
A field of white mustard in Crete
White mustard flowers
White mustard seeds
Probably the Mediterranean.
White mustard probably originates from the Mediterranean region, but various cultivars are grown in Northern, Central and Eastern Europe where it was introduced during the Middle Ages under Charlemagne's herbal decree, the Capitulare de Villis. Related species include Chinese mustard s. cernua from China and rocket eruca sativa from Southern and Eastern Europe.
Seeds. Although called "white mustard", the seeds are actually yellow to light brown in colour.
Brassicaceae (cabbage family).
The dried seeds do not have any fragrance but exhibit a pungent taste after being chewed for a while.
For the etymology of mustard, see Mustard, Black. Species name sinapis is Latin for mustard, from the Greek sinapis. Species name alba is from Old English albe, from the Latin alba (feminine of albus "white").
White mustard seeds are mostly used for the preparation of mustard pastes, for which purpose they are superior to black mustard because their pungent principle p-hydroxy-benzyl-isothiocyanate is non-volatile and stable to hydrolysis in an acidic environment. Mustard is usually made of crushed or ground mustard seeds with vinegar (to stabilise the pungency) and wine (the selection of which is crucial to the mustard's taste). Frequently sugar or honey, fresh herbs and dried spices are added to modify the taste, the most common being tarragon. Some brands of mustard contain turmeric to give the product a bright yellow colour.
Mustard paste is a common condiment for boiled or broiled meat in Central and Northern Europe and the US and is often used for sauces. As mustard seeds contain emulgators, mustard improves both the flavour and the stability of emulgated sauces (e.g. sauce Hollandaise).
The mustards produced in Britain, France and Germany have a distinct style. British mustard is mostly produced by the Colman method, which has been the dominant mustard technique for about 200 years. Black mustard is finely ground and sieved together with small amounts of white mustard and wheat flour to improve the texture. The mixture is traditionally sold dry and mixed with water shortly before use, developing the flavour within ten minutes (a similar process is used in Japan with wasabi).
In France, there are two different traditional types of mustard pastes. The pale Dijon mustard is made from decorticated seeds of black mustard, finely ground, mixed with sour grape juice (verjus) and salt. It is pungent, sour and quite salty and fits very well to braised or roast meats. Dijon is the kind of mustard called for by the numerous sauce recipes prepared in France.
The milder Bordeaux type mustard is made of white mustard seeds without their seed coats removed and is darker than the Dijon type. It contains vinegar, sugar and various herbs and spices typically including tarragon. There are also less traditional mustard varieties in France that owe their particular flavour to additional ingredients such as champagne or fiery Basque chillies.
Germany offers two main types of traditional mustard pastes. Düsseldorf (the mustard capital of Germany) produces a pungent mustard löwensenf "lion's mustard", similar to Dijon, which is made from pure black mustard seeds. The sweet Bavarian mustard is prepared from coarsely ground white mustard seeds, honey and various herbs and is the mustard to eat with weißwurst, typical Bavarian veal sausages. A large number of mild, smooth mustards are also produced from ground white mustard seeds, often flavoured with tarragon.