In appearance, yams are rather like sweet potatoes but they taste more like ordinary potatoes when cooked. They are the tubers of a tropical vine which originated in China but is now found throughout the Pacific, the West Indies and Africa. To cook: Yams can be baked, boiled or fried. They may be baked whole, in their skins, but should be peeled before boiling or frying. Yams quickly discolour when peeled, so drop into cold acidulated water (water with a little lemon juice or vinegar added) as soon as peeled. Add a little lemon juice to the water when boiling, too.