How to select for best flavor:
Select firm, medium-sized yams that taper at both ends. Larger yams are good for baking or barbecuing, although they tend to be tougher and can even be stringy. Avoid shriveled or sprouting yams and yams that have cracks or mold.
Peak of the season:
One variety or another is available all year. The peak season for yams comes in November, right before Thanksgiving.
The nutritional value of a yam can vary widely based on its type, where it was grown and the weather. Generally yams are a good source of vitamins A and C, protein and iron. One cooked yam will have between 115-165 calories, almost no fat and 11 mgs. of sodium.
Most yams that you will see for sale are not yams at all but certain varieties of sweet potato. The true yam grows in the tropics, is not biologically related to the sweet potato, and is almost unknown in the United States.
In the U.S., the sweet potatoes sold as yams are moister and sweeter than what are sold as sweet potatoes. The pulp is dark-orange and the skin will be a deep brown or coppery color. Cold, steamed yam with salt is a great snack and very popular in Japan.