by Linda R. (NC) » Fri Feb 02, 2007 7:13 pm
Here is something I found a while back that explains the difference between sweet potatoes and yams.
Sweet Potato
Definition: This large edible root belongs to the morning-glory family and is native to tropical areas of the Americas. There are many varieties of sweet potato but the two that are widely grown commercially are a pale sweet potato and the darker-skinned variety Americans erroneously call "yam" (the true yam is not related to the sweet potato).
The pale sweet potato has a thin, light yellow skin and a pale yellow flesh. Its flavor is not sweet and after being cooked, the pale sweet potato is dry and crumbly, much like a white baking potato. The darker variety has a thicker, dark orange skin and a vivid orange, sweet flesh that cooks to a much moister texture. Fresh sweet potatoes are available sporadically throughout the year, though not as readily during the summer months.
Canned and frozen sweet potatoes are available year-round and are sometimes labeled as yams. When buying fresh sweet potatoes choose those that are small- to medium-sized with smooth, unbruised skins. Sweet potatoes don't store well unless the environment is just right, which is dry, dark and around 55 degrees F. Under perfect conditions they can be stored for 3 to 4 weeks. Otherwise, store in a cool, dark place and use within a week of purchase. Do not refrigerate.
Sweet potatoes--particularly the pale variety--can be substituted for regular potatoes in most recipes. They can be prepared in a variety of ways including baking, boiling and sautéing. Sweet-potato chips can now be found on some restaurant menus. Sweet potatoes are high in vitamins A and C. See also potato.
Yams
Definition: This thick, tropical-vine tuber is popular in South and Central America, the West Indies and parts of Asia and Africa. Although sweet potatoes and yams are similar in many ways and therefore often confused with one another, they are from different plant species. In the southern United States, sweet potatoes are often called yams and to add to the confusion, canned sweet potatoes are frequently labeled yams. True yams, however, are not widely marketed and are seldom grown in the United States. Though they can be similar in size and shape to sweet potatoes, yams contain more natural sugar and have a higher moisture content. On the downside, they're not as rich in vitamins A and C as sweet potatoes.
There are over 150 species of yam grown throughout the world. They can range in size from that of a small potato to behemoths over 7-1/2 feet long and 120 pounds. Depending on the variety, a yam's flesh may be various shades of off-white, yellow, purple or pink, and the skin from off-white to dark brown. The texture of this vegetable can range from moist and tender to coarse, dry and mealy. Yams can be found in most Latin American markets, often in chunks, sold by weight. When buying yams, select unblemished specimens with tight, unwrinkled skins. Store in a place that's cool, dark and dry for up to 2 weeks. Do not refrigerate. Yams may be substituted for sweet potatoes in most recipes.