Coriander is one of the oldest of the spices used in Indian cooking. Its history can be traced back to the earliest written recipes.
It is not a seed, but the fruit of the coriander plant. When ripe, the fruit are yellowish-brown or tan in colour with longitudinal ridges. They are then dried, producing the seed-like appearance.
The coriander seed has a warm and subtle flavour with a slight citrus hint. It has an aromatic scent that is soothingly warm, nutty, slightly fruity, and complex.
Roasting or heating the seeds in a dry pan heightens the flavour, aroma, and pungency. Ground coriander seed loses flavour quickly in storage and is best prepared fresh.
Coriander seeds are available everywhere, but I strongly recommend buying them from a specialist spice merchant. Their flavour is so important to Indian cooking, and it would be a shame to use anything but the best you can get.