Turmeric is the culinary appellation for the root of the plant Curcuma longa. The root of Curcuma longa is used for several applications. A member of the ginger family, turmeric is primarily used as a spice in South Asia--it's what gives curry its yellow color. However, it is also used for its medicinal properties and as a dye. For best results, Thai Food & Travel recommends using the whole fresh root when preparing turmeric root as a food dish, dye, cosmetic or medicinal herb.
Boil the whole turmeric root in water until a fork can penetrate the root with just a little resistance (usually 5 to 10 minutes).
Place the boiled turmeric root in a cool, dry place to air dry. Depending on the humidity in your area this may take several days or a week or more.
Peel the turmeric root with a vegetable peeler.
Grind the turmeric to a fine powder with a fine grater.