The terms "yam" and "sweet potato" are used almost interchangeably, but yams and potatoes are actually different, unrelated plants. And sweet potatoes are not even related to white, or Irish, potatoes.
In the United States, we usually buy a sweet potato when we think we are buying a yam. Even canned "yams" are actually sweet potatoes, and the U.S. Department of Agriculture stipulates that the words "sweet potato" accompany the word "yam" on food labels. Yams are rarely grown in the United States. If you want to find a true yam, a Latin American food market is your best bet.
Yams and sweet potatoes look alike, both are tuberous roots, and the ones sold in most markets are the size of large white potatoes. Hundreds of species of yams grow around the world, and most tend to be fibrous and starchy. In contrast, sweet potatoes are typically sweet and moist. Sweet potatoes have more vitamin A and vitamin C than yams do, which is a nutritional plus. Sweet potatoes are also good sources beta carotene, which the body converts to vitamin A, as well as vitamin B6, folic acid, dietary fiber, potassium and manganese.
Nutritionists recommend sweet potatoes over white potatoes because the vitamin and mineral content of the sweet potato is higher. Sweet potatoes also have a lower glycemic load than white potatoes. This means that the sweet potato has less effect on blood sugar and blood insulin levels than white potatoes do, and nutritionists consider this a healthy characteristic of these root vegetables.
We'll confine our discussion to sweet potatoes from this point, since the "yam" that Americans most often purchase in the market is nearly always a deep orange, moist sweet potato.
Sweet potatoes are versatile. To eat them plain, try baking, broiling, microwaving, grilling or boiling them. Some grocery stores sell frozen sweet-potato fries, and these are available at some restaurants too. Bags of veggie chips usually contain some sweet potato chips. In general, you can cook with sweet potatoes in the same way that you cook with white potatoes. Try adding them to soups, stews and casseroles. Sweet potatoes make a less-sweet alternative to pumpkin pie filling.
What to Look for
Sweet potatoes or "yams" can have dark or light skins. The dark-skinned variety has a deep orange skin that is quite thick. Its flesh is usually deep orange, sweet and succulent. Light-skinned varieties have more of a yellowish skin and a dryer, yellow flesh. Look for sweet potatoes that are heavy and solid. Avoid ones with wrinkled skins or obvious blemishes, as well as those with sprouts or mold.
Common Pitfalls
Don't refrigerate sweet potatoes. Over-cooling can make them difficult to cook through. Storage in a cool spot away from direct sunlight is sufficient.
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