The walnut-sized corm of an aquatic plant native to Southeast Asia, water chestnuts have dark-brown skin and a crisp, white, mildly sweet flesh, eaten raw or cooked. Bought fresh or in tins, water chestnuts add texture to Asian cooking, especially in minced meat dishes, stir-fries, won tons or sweet dishes. They are usually cooked quickly to retain their crisp texture, for which they are prized. Tinned chestnuts keep in a jar covered with water for up to 1 week (change the water daily), or can be frozen.