In cooking, skin refers to the outer covering of poultry, fish, or produce, used either as an edible, often crisped component of a dish or removed and discarded before cooking. Poultry and fish skin render well: slow, dry heat melts the fat beneath the skin and crisps the surface, as in roast duck or pan-seared salmon. Fruit and vegetable skins, such as citrus zest, grape skins, or potato skins, are used raw or cooked for their flavor, color, or texture, and are sometimes left on for nutritional reasons. Because skin carries most of an ingredient's fat, dishes built around it, like crispy duck skin or fried chicken skin, tend toward rich and savory, while fruit and vegetable skins lean bright or slightly bitter.