Cardamom is an Asian shrub in the ginger family. It grows long, pointed leaves off a large stem, similar to tulips or iris. Its tropical flower makes way for plump seed pods that contain the pungent, oil-rich cardamom seeds. The pods are picked by hand when green, and dried in the sun. They’re sold green, which are not processed beyond natural drying, and white, which are treated with sulfur dioxide to mute the flavors.
Black cardamom has a completely different smoky, peppery quality because it’s dried over open, smoky flames. It can hold up well to, and is preferred for, heavier, spicier dishes than the green or white pods. That said, there’s no need to run to the store for black if all you’ve got is green.
Cardamom is popular in India, where it’s a common ingredient in curries and rice dishes. Scandinavian and Bavarian chefs know cardamom well and take advantage of its sweet overtones in fruits, breads, and pastries. It’s also a key ingredient in strong, cloyingly sweet Turkish coffee.
Ground cardamom is widely available, and white pods can be found in better markets. Green and black may take a little more time to track down (savoryspiceshop.com).
It’s always better to buy spices whole if possible. Once ground they lose their flavor rapidly, but whole, they will keep forever. (I still use a stash of whole cardamom pods I bought on my honeymoon in 1989.) To use whole cardamom, break open the pod, and remove the tiny seeds inside. It’s best to grind them in a small mortar, but use a coffee grinder if you have a lot to grind.