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The spice is generally made from ground seeds of the plant, with the seed coats removed. The small (1 mm) seeds are hard and vary in color from dark brown to black. They are flavorful, although they have almost no aroma. The seeds are commonly used in Indian cuisine, for example in curry, where it is known as rai. The seeds are usually thrown into hot oil or ghee, after which they pop, releasing a characteristic nutty flavor. The seeds have a significant amount of fatty oil. This oil is used often as cooking oil in India.
Ground seeds of the plant mixed with honey are widely used in eastern Europe as cough suppressant. In Eastern Canada, the use of mouche de moutarde to treat respiratory infections was popular before the advent of modern medicine. It consisted in mixing ground mustard seeds with flour and water, and creating a cataplasm with the paste. This cataplasm was put on the chest or the back and left until the person felt a stinging sensation.
The plant itself can grow from two to eight feet tall, with racemes of small yellow flowers. These flowers are usually up to 1/3" across, with four petals each. The leaves are covered in small hairs; they can wilt on hot days, but recover at night.
Since the 1950s, black mustard has become less popular as compared to India mustard because some cultivars of India mustard have seeds that can be mechanically harvested in a more efficient manner.
Similar plants 
B. nigra also resembles Hirschfeldia incana, or hoary mustard, (formerly Brassica geniculata), which is a perennial plant.
See also 
- Zemede Asfaw, "Conservation and use of traditional vegetables in Ethiopia", Proceedings of the IPGRI International Workshop on Genetic Resources of Traditional Vegetables in Africa (Nairobi, 29–31 August 1995)
- Post, George Edward (1900). "Mustard". In James Hastings. A Dictionary of the Bible.
|Wikimedia Commons has media related to: Brassica nigra|
- Entry in Gernot Katzer's spice pages, with pictures and detailed information
- Entry in Illinois Wildflowers