Two types of sweet potatoes are available in varying amounts the year round.
Moist sweet potatoes, sometimes called yams, are the most common type. They have orange colored flesh and are very sweet. The true yam is the root of a tropical vine which is not grown commercially in the U.S.
Dry sweet potatoes have a pale colored flesh, low in moisture.
Most sweet potatoes are grown in the Southern tier and some Eastern States, in an area from Texas to New Jersey. California is also a heavy producer.
When buying look for well-shaped, firm sweet potatoes with smooth, bright, uniformly colored skins, free from signs of decay. Because they are ore perishable than Irish potatoes, extra care should be used in selecting them.
Avoid sweet potatoes with worm holes, cuts, grub injury and any other defects which penetrate the skin; this causes waste and can readily lead to decay. Even if you cut away the decayed portion, the remainder of the potato flesh which looks normal may have a bad taste. Decay is the worst problem with sweet potatoes and is of three types: wet, soft decay, dry firm decay which begins at the end of the potato, making it discolored and shriveled; and dry rot in the form of sunken, discolored areas on the sides of the potato. Sweet potatoes should not be stored in the refrigerator.