YELLOW or WHITE MUSTARD: (Sinapis alba). ‘‘Sinapis‘ is the Greek name for mustard and the word from which the German word for mustard, ‘‘senf‘, is derived. (The species may also be offered as ‘‘Brassica alba‘ or ‘‘B. hirta’) This is the species whose seed is most commonly used in American prepared mustards. (The brassy yellow color or many prepared mustards comes from the addition of turmeric or other food coloring.) Although some yellow mustard seed is used in English mustards, it is forbidden in the classic Dijon mustards. The seeds, which are a warm beige and somewhat larger than those of black and brown mustards, are sometimes sprouted for use in salads. Plants usually grow 1 to 2 feet tall.
BLACK MUSTARD: (Brassica nigra). The seeds of black mustard are dark brown and about 1/16 inch in diameter. The black mustard plant can grow as tall as 10 feet, but 5 or 6 feet is more usual. This is the most pungent of the mustards and a prolific seed producer, but its height and the instability of its pods make it difficult to harvest with machinery. Thus, it is not widely cultivated commercially and is available mostly through specialty stores.
BROWN MUSTARD: (B. juncea). Brown mustard seeds are similar in size and color to those of black mustard, but significantly less pungent. The plant is only about half as tall as black mustard (about 4 feet) and much more easily cultivated, and it has largely replaced black mustard as a cultivated crop. Some 250,000 acres of prairie in Canada are planted to brown and yellow mustard. Numerous cultivars of this species have been bred for their lively, nutritious greens, which are especially highly regarded in Asia, but these are not the cultivars used for seed production.