Mustard seed comes from one of a number of members of the brassica family of plants (you know cabbage, sprouts, broccoli - that mob); the seeds come in three colours - white (which are actually yellow but called white), brown and black; they are three different but related plants. The seeds are amongst the smallest of seeds references to them in religious writings use this to signify humility.
In Europe it is primarily the yellow one, sometimes mixed with black seeds that we use to make table mustard, Dijon mustard is made from hulled black mustard. It is the brown and black varieties that are used in Indian food and although they are different - the black is more pungent than the brown for example - they are used fairly interchangeably.
The seeds themselves have very little aroma, the aroma is awoken by frying in hot oil which cracks the seeds and releases it. The taste is very sharp and hot..
it was known to the Chinese many thousands of years ago and was a common condiment to the ancient Greeks. Although believed to be native to the southern Mediterranean, the plant has been known to the Indian kitchen for at least 2,500 years.
Incidental bit of trivia - the plant was originally called senvy and was mixed into a paste with unfermented wine - called must - hence mustard
The seeds are used whole, ground and importantly to make mustard oil.
When the seeds are used whole they are dropped into hot oil, this makes them pop and release their sharp aroma and strong nutty flavour. This is done with many dishes such as aloo bhaji. They are also fried like this with other spices to use as a garnish for a dish. The whole seeds are also used in pickling - for example in lime pickle.
They are an important ingredient in curry powder where they are ground with other spices. The ground seeds can also be used to make a paste with water; in Bengal mustard seeds are ground like this together with chillies and ginger to make a pungent paste. In Andhra they use mustard paste on all sorts of vegetables (ava kooralu) and even raw mango (avakaya).
The ground seed is sometimes called mustard flour and is the basis for table mustard. Interestingly this flour is almost completely tasteless, it is only when water is added that enzymes get to work to produce the pungent smell and taste.
Mustard oil is usually made from the brown mustard seed and is very common in Indian cooking and produces the tastiest curries.
Nutritionally mustard seeds have lots of minerals and especially trace minerals such as selenium, zinc, manganese and magnesium. They are also a source of omega-3 fatty acids, protein, and fibre.
The medicinal properties of mustard are also renowned. It was believed by the Greeks to be a gift to mankind from their god of healing (Asclepious, bet you knew that really). It has been (and still is) used for making poultices for healing wounds, and for ailments ranging from stomach disorders to toothaches and even snake and scorpion bites.
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