The dried seed do not have any fragrance, but exhibit a pungent taste after some time of chewing. Roasted seeds (more gray in colour) have a rich, nutty odour.
Black mustard contains about 1% sinigrin (allylglucosinolate), a thioglycoside-like compound (a so-called glucosinolate) of ally isothiocyanate with glucose. By action of the enzyme myrosinase, allyl isothiocyanate, a pungent, lachrymatory and volatile compound, is liberated (0.7% of the dried seed). Besides allyl isothiocyanate, in Romanian Brown Mustard another related compound is found, namely crotonyl isothiocyanate (2-butenylisothiocyanate).
Isothiocyanates are also the main ingredients of white mustard, horseradish, wasabi, rocket and cress, all of which belong to the same plant family. The more distantly related capers similarly owe their pungency to an isothiocyanate.
Note that isothiocyanates are aggressive substances that have the function of a chemical weapon against herbivorous animals. They are dangerous also to plants; therefore, the isothiocyanates are stored in the plant organism as glucosinolates (formerly called thioglycosides) which are harmless. The free isothiocynates are quickly formed by enzymatic reaction whenever the plant tissue gets damaged. Although the chemical details are much different, the basic functionality of this defence system is similar to that found in cyanide-producing plants like almond.
Black mustard fruits
Ripening black mustard pods
Black mustard flowers
Like all seeds, mustard seeds contain also significant amounts of fatty oil (30%), which is used extensively for cooking in India (beware: the term mustard oil is both used for this fatty oil and the pure isothiocyanates). Besides glycerides of linoleic and linolenic acid, mustard oil contains glycerides of erucic acid, which is considered harmful to human health; furthermore, traces of free isothiocyanates may be found in mustard oil. Therefore, despite its high fraction of unsaturated fatty acids (iodine index is 105), mustard oil cannot be recommended without qualification for cooking purposes (see also below).
Black mustard is probably endemic in the Southern Mediterranean region, but has been cultivated since thousands of years; therefore, numerous cultivars are found.
Botanically different, though of equal use in the kitchen, are the Sarepta mustard or Romanian Brown Mustard (Br. juncea) from Eastern Europe and the Indian Brown Mustard (Br. integrifolia or Br. juncea, a fertile hybrid from Br. nigra and Br. campestris) from India and Central Asia. Of all three species, the latter is probably most commonly sold in the West.
Although the pungency of black mustard is slightly stronger than that of brown mustard, black mustard is hardly planted in Europe anymore, and brown mustard is the dominating quality on the European market. The reason is that brown mustard, unlike black mustard, can be harvested by machines which make production much cheaper in countries where working force is expensive.
The German Senf is a loan from Latin sinapi, as well as the Old English senep (preparation of mustard paste was introduced to central and Northern Europe by the Romans). The Latin term is probably from Greek (sinapi [σίναπι], also napy [νᾶπυ]); loans in other European tongues include Italian senape, Swedish senap and Yiddish zeneft [זענעפֿט]. The ultimate origin of sinapi is not known; possibly, it is Egypt, but another theory links it to Sanskrit sarshapa [सर्षप], identifying the latter as a non-Indo-European loan of Central Asian provenience. In that case, Malay sawi might be akin.
Sinapi is also the word used in the New Testament for “mustard”; it appears in the famous Parable of the Mustard Seed found in all synoptic gospels. Yet, Matthew and Luke compare mustard with a bird-housing tree (dendron [δένδρον], see also juniper for more linguistic notes) which is hardly tenable, as mustard is an annual herb whose tender branches cannot support birds. Mark gets the facts better when he calles the mustard plant “the largest of all garden plants” (lachanon [λάχανον]) and places the birds in the shadow of the branches on the ground below the plant. See also pomegranate about plants in the Bible.
Mustard (and similar words in Romance languages, and the German Mostrich for mustard paste) is derived from Latin (vinum) mustum, “must”. Although mustard paste is today predominantly prepared with vinegar and wine, the Romans (who made mustard seeds popular in Central and Western Europe) used must (young wine).
Lastly, the genus name Brassica is Latin for “cabbage”, which belongs to the same genus. The origin of that word is dark.
It is theorized that black mustard is the seed mentioned by Jesus in Matthew 13:31-32.