Mustard is an annual herb cultivated as oil seed crop, as a vegetable or as fodder.
The leaves of the plant are used often in Indian cooking and are referred to elsewhere.
The seeds are used in recipes from the south and the eastern coastal regions. Bengali cooking in particular features mustard seeds – and the leaves, and the oil derived from the seeds.
There are four species of mustard which are known for their condiment value. They are white mustard (Brassica alba), yellow mustard (Brassica hirta), brown mustard (Brassica juncea) and black mustard (Brassica nigra).
Generally speaking, it is the black mustard seeds which are used most often in Indian cooking, with the brown coming a close second. The white and yellow seeds are usually only used when making pickles or chutneys. When cooking, the whole seeds are fried quickly in oil, to give a hot, nutty and spicy flavour once the seeds have popped. This process of frying whole spices in oil to release their flavour and aroma is called as tempering, or chaunk, and is discussed elsewhere in this book.
Black mustard seeds are generally available from supermarkets and Indian grocers. To make sure you get fresh, black, not brown, mustard seeds, you should buy these from a specialist spice merchant.