Black mustard

Black mustard is a tall annual herb, often growing to two metres or more, with bright yellow four-petalled flowers that form slender pods pressed close against the stem. The pods hold tiny round seeds, one to two millimetres across, dark reddish-brown to black.

Whole seeds are nearly odourless until crushed and mixed with water, when an enzyme reaction forms a hot, nose-clearing pungency from compounds called isothiocyanates, particularly allyl isothiocyanate.

The seeds are sold whole, ground and as part of prepared mustards, though today most black mustard sold is actually brown mustard or a mix.

Black mustard is probably native to the Mediterranean region and parts of southwestern Asia and has been cultivated since ancient times. It is now widespread as a weed and crop in temperate areas of Europe, Asia and North Africa and has been naturalised in the Americas.

Botanists have changed its name several times, and it may appear as Sinapis nigra or Rhamphospermum nigrum in older and newer literature.

The English word mustard comes from Old French moustarde, from Latin mustum, the grape must that was mixed with ground seeds to make a paste in Roman times.

Mustard seed is mentioned in ancient Greek, Roman and Indian sources, and Roman cooks mixed ground seed with unfermented grape juice, from which the word mustard derives. Roman armies are thought to have spread mustard cultivation across Europe, and by the Middle Ages, mustard making was a notable craft in France, notably Dijon, and in England, the Low Countries and Germany.

Black mustard was the main species used in European mustard until the 20th century. The plants shatter their pods easily, which makes machine harvesting hard, so growers moved to brown mustard types that hold their seed. In English mustard-making towns such as Norwich and Durham, black mustard formerly formed a big part of the blend.

In Indian cooking, mustard seeds, whether black or brown, are tempered in hot oil, and mustard oil is a regional staple in Bengal and northern India.

In the New Testament, the tiny mustard seed became a symbol of faith, and in medicine, mustard plasters of ground seed were a traditional remedy for chest complaints.

Seeds are tempered whole in hot oil to bring out a nutty flavour in Indian curries, dals, pickles and chutneys, or ground with water and vinegar for prepared mustards. They are pickled in jars with spices and added to marinades and brines.

Black mustard has been traditionally used in plasters and baths to warm the skin.

The seeds also yield mustard oil, widely used in cooking in parts of South Asia. Leaves and young shoots are eaten as greens in some regions.

Mustard seeds contain glucosinolates, which, when the seed is crushed and wet, form isothiocyanates that are being investigated for antimicrobial and cancer-preventive properties in laboratory studies. Human evidence for specific benefits from culinary amounts is limited.

The seeds provide small amounts of fibre, selenium and minerals. As a spice, they add flavour without much salt or fat, which can help in lowering reliance on other seasonings.