Yams - Sweet Potato
Ninety percent of what you see in the stores marked "yams" is actually a variety of sweet potato. The true yam is a tuber that can get as large as 100 pounds and grows primarily in the tropical zones of Africa. The potato with the sweet orange-red flesh that grows in the American South was dubbed a yam by African slaves, and the name stuck.
American sweet potatoes are members of the morning glory family. The rich orange-fleshed variety is harvested beginning in August; the fresh ones that show up on the market then have not been cured. The bulk of the crop is held in a heated, humidity-controlled environment for about a week. This "cures" the potato and converts much of its starch to dextrin and sugar. A cured sweet potato is actually much sweeter than an uncured one and is what usually shows up on the Thanksgiving table.
There are two other varieties of sweet potato that are much less frequently seen these days than the one that masquerades as a yam. The red sweet potato has a yellow flesh that's a bit sweeter than the white sweet potato, which has a white, more fibrous flesh. The red sweet potato has a dark, reddish skin and is in season about the same time as the yam type - starting in September. It keeps better than the white sweet potato, which has a very short season - usually the last couple of weeks in August.
Avoid buying sweet potatoes in June and July, by then most of them have been stored for nearly a year. Uncured sweet potatoes start showing up on the market in late August; cured sweet potatoes arrive around the end of October. By Thanksgiving almost all that are on the market have been cured. The less common white and red sweet potatoes have a much shorter season at the end of the summer.
Look for bright-colored, un-bruised skin with no soft spots. Look at the ends of the potatoes, which should be firm. Most sweet potatoes have some fibrous roots on them; these are not a problem.
Recipes with Yams - Sweet Potato
Catherine's Sweet Potato Pie
Other recipes from Produce Pete.