Saffron is the dried stigma and part of the style of the saffron crocus. It has a pleasant spicy smell, and it contains a dye that colours food a distinctive deep golden colour. It is one of the most expensive of all spices, because of the labour-intensive way it is prepared. Saffron has been described as metallic honey with grassy or hay-like notes, while its taste has been noted also as hay-like and somewhat bitter. Saffron contributes a luminous yellow-orange colour to whatever you put it in.
Saffron is used in many Spanish recipes, including paella and fabada Asturiana, and in the most famous saffron-based Italian dish, the risotto alla milanese. Outside Europe, it is a vital ingredient of many South and Central Asian, and Arabian dishes.
Turmeric is sometimes used as a substitute; although it gives a similar colour, it has none of the real saffron taste.
Saffron should always be soaked in hot (not boiling) water before use, about three times as much water as saffron. If you have the time, it is best to soak the whole saffron strands for about 2 hours. Otherwise, soak for at least 20 minutes, then crush the strands of saffron with the back of a spoon, to release the flavours and colour in to the water. Add the saffron and soak water to the rest of the ingredients, as directed by the recipe.