A key ingredient in bouillabaisse and paella, saffron has the reputation of being the most expensive spice by weight in the world. The stigma of a little purple perennial crocus flower, it must be gathered by hand during a harvest that lasts just a couple of weeks in the fall, and there are only three stigmas per blossom. It takes about 75,000 flowers to yield a pound of saffron. Fortunately, a pinch (about 20 threads) is usually all it takes to impart saffron's distinctive yellow color and vaguely metallic, dried alfalfa hay and bittersweet wildflower-honey flavor. Saffron is featured in Spanish and Indian cooking; it's often a major component of curry powders; Iran, Greece, Morocco, and Italy also harvest and use saffron, too.
There's no spice that mimicks saffron's flavor, but turmeric or annatto seeds will impart a similar golden-yellow color.
When buying saffron, keep two rules in mind. First, buy saffron in threads only. Powdered saffron can contain other products, and it's difficult to know whether you're buying the pure spice. Second, look for saffron that contains only short, deep red threads, which is sometimes called coupé . Lesser grades of saffron include threads with some yellow areas (which is the style part of the flower). This isn't a bad thing, but the yellow part doesn't have the same coloring and flavoring power as the red stigmas, so the saffron isn't as potent.
Liquid helps draw out the flavor and color from saffron, so crumble it directly into broths, sauces, or soups. If using in something less fluid, let it steep in a little hot water for a few minutes first and add the water and saffron to the dish. You can also infuse oil with saffron, but the flavor and color won't come though as well as they do in water.
Stored in a sealed container in a dark place, saffron should last a couple of years before the flavor starts to diminish.