Brown mustard

Brown mustard is a fast-growing annual herb up to a metre or more tall, with large, lobed lower leaves and bright yellow flowers. It sets slender pods that hold small round seeds, about one to two millimetres across, in reddish-brown or dark brown, sometimes yellowish in some varieties.

Whole seeds are mild until they are crushed and moistened, when they develop a sharp, pungent heat that is more intense than that of white mustard, though milder than black mustard.

They are sold whole, cracked, ground as mustard flour, as oil and as a base of prepared mustards. The leaves of other varieties are eaten as mustard greens.

Brassica juncea arose through a natural hybridisation of two other Brassica species, Brassica rapa (turnip type) and Brassica nigra (black mustard). It is thought to have emerged in Central Asia, with Southwest Asia and India also proposed as centres of origin.

It spread widely and diverged into many cultivated forms, such as oil-seed types in India and China, leaf mustards in East Asia and spice types in Europe.

The word juncea means rush-like, referring to the slender stems. Brown mustard seed is sometimes called rai in Hindi and is often confused with black mustard in the spice market.

Brown mustard has been cultivated for thousands of years in Asia, and archaeological finds in the Indus Valley suggest that mustard-type seeds were used there. In India, it is a major oilseed crop, and mustard oil has been the traditional cooking fat of Bengal, Punjab and Kashmir.

In Europe, brown mustard gradually replaced the shattering-prone black mustard in the 20th century, as machine-harvestable varieties were developed, and it is now the seed used in Dijon-style mustards and many other prepared mustards. Canada and Russia are leading producers of the condiment seed today.

Leaf mustards of the same species are important vegetables in Chinese, Japanese and Southern American cooking, including the fermented pickle zha cai and Southern mustard greens.

The plant has also been studied for phytoremediation, since it can accumulate heavy metals in the soil, and is used as a biofumigant cover crop.

Seeds are tempered in hot oil to release a nutty, bitter-sharp flavour in Indian dals, vegetable dishes and pickles, or ground with vinegar, wine, water or verjuice to make Dijon-style and other brown mustards. They are used whole in pickling brines and sausages.

Mustard oil is used for cooking and massage in northern and eastern India. Leaves are eaten as greens and the stems are pickled in East Asia.

Mustard powder is used in dry rubs and sauces, and plasters made from it have been a traditional home remedy.

Brown mustard seeds contain glucosinolates, such as sinigrin, which form pungent isothiocyanates upon crushing, and these compounds are studied in the laboratory for antimicrobial and cancer-related effects. Seeds also provide small amounts of selenium, magnesium and fibre.

Culinary amounts are not shown to treat disease. Mustard oil in India has been studied for effects on cardiovascular health, with mixed evidence, partly due to its erucic acid content.