There are two main types of sweet potato: dry-fleshed and moist-fleshed, though you rarely see these terms used in a market.
The starchier, dry-fleshed types have a tan skin and light-colored flesh ranging from almost white to a light yellow. Their texture is much more akin to baking potatoes.
The moist-fleshed sweet potatoes have a dark, red-brown skin with orange to deep-orange flesh. This type dominates the market, perhaps because they are sweeter. There is rarely any distinction in the market among sweet potatoes, except for the following:
Batata sweet potatoes: This dry-fleshed sweet potato is rounder than American sweet potato types and has a mottled red-purple skin. The batata’s name is taken from the species name for all sweet potatoes: Ipomoea batatas. It is a favorite in Puerto Rican and other Latin American cuisines.
Boniato (Cuban sweet potatoes): A boniato is a white sweet potato similar to a batata. Boniatos can be found in Hispanic markets, especially in Cuban neighborhoods.
Jersey sweet potatoes: There are a number of varieties of dry-fleshed sweet potato that include Jersey in their varietal name (for example, Big Stem Jersey and Little Stem Jersey) and some markets will identify any dry-fleshed sweet potato as a Jersey or Jersey sweet.
Kumara sweet potatoes: Another tropical sweet potato, kumara is what the sweet potato is called in New Zealand. The traditional variety of sweet potato grown there is called the Owairaka Red, which is a direct descendant of an American sweet potato introduced to New Zealand in the 1850s by an American whaling ship. The kumara has red skin and white flesh.
White sweet potatoes: This is a generic term used to identify what are loosely called tropical sweet potatoes. Their flesh is lighter in color than orange-fleshed sweet potatoes. Although it all started with a North American plant, the sweet potato has been adapted to many tropical regions around the world. Depending on where the sweet potato comes from it may be called batata, kumara, camote, or boniato, to name a few.
Yams: Moist-fleshed sweet potatoes are often called “yams,” but this is a misnomer. Yams are a completely different starchy tuber. Nonetheless, common usage has made the term “yam” acceptable when referring to sweet potatoes. Although the USDA requires that the label “yam” always be accompanied by the term “sweet potato,” this is frequently disregarded in stores.
How to choose the best sweet potatoes
Select sweet potatoes that are heavy for their size, and, if you plan to cook them whole, buy similar-sized potatoes of the same variety. This will keep the cooking time uniform. Also, don’t mix dry- and moist-fleshed types of sweet potatoes.
Choose potatoes that are smooth, hard, and free of bruises or decay. Decay may appear as shriveled or sunken areas or black spots. Even if cut away, a decayed spot may have already imparted an unpleasant flavor to the entire potato.
How to store sweet potatoes
Despite their rugged appearance, sweet potatoes have a thin skin that is easily damaged, and they are subject to rapid spoilage. To help preserve sweet potatoes, growers cure them by storing them at a high temperature and humidity for about 10 days before sending them to market. This process also enhances the vegetable’s natural sweetness.
After purchase, sweet potatoes should be kept in a cool (55°F to 60°F), dry place, such as a cellar, pantry, or garage. Never store sweet potatoes in the refrigerator, where they may develop a hard core and an “off” taste. In fact, when sweet potatoes are stored at low temperatures, their natural sugars turn to starch, which does nothing to enhance their flavor.
Sweet potatoes will keep for a month or longer if stored at 55°F. If kept at normal room temperature, sweet potatoes should be used within a week.