Turmeric is native to tropical South Asia - Plants are gathered annually for their rhizomes, and propagated from some of those rhizomes in the following season.
When not used fresh, the rhizomes are boiled for several hours and then dried in hot ovens, after which they are ground into a deep orange-yellow powder commonly used as a spice in curries.
Its active ingredient is curcumin and it has a distinctly earthy, slightly bitter, slightly hot peppery flavor and a mustardy smell. Curcumin can be used to test the alkalinity or acidity of foods. It turns yellow in an acidic food, and it turns red in an alkaline food. Ayurveda has recommended its use in food for its medicinal value.
Leaves of turmeric are used to wrap and cook food. This usually takes place in areas where turmeric is grown locally, since the leaves used are freshly picked. This imparts a distinct flavor. Turmeric is widely used as a spice in South Asia.
In Goa and Dakshina Kannada (Karnataka state, India), turmeric plant leaf is used to prepare special sweet dishes, patoleo, by layering rice flour and coconut-jaggery mixture on the leaf, and then closing and steaming it in a special copper steamer.