Although they look alike and have taste similarities, sweet potatoes and yams are from different plant families. The former are from the morning glory family, while yams are part of the lily and grass family called Dioscorea. The misunderstanding started in the 1930s, when sweet potato farmers in the Southern United States, in order to differentiate the harder, white- or pale-fleshed sweet potatoes from the softer, orange varieties, called the latter yams, confusing everyone.
Grocery stores sometimes mislabel them. Sweet potatoes are what we generally find in markets. They have tapered ends, the skin colour varies from pale yellow to deep orange and their flesh usually matches the outside skin. The flesh of orange sweet potatoes tends to be sweeter and creamier than that of pale yellow or purple ones. The paler ones are starchier, more like a potato. The red ones with a red interior have more moisture, but a similar taste to the orange ones.
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Bruised sweet potatoes rot very quickly, so choose ones with unblemished skins as they do not store well, keeping only about a week at room temperature. If you have a cold cellar, this is an ideal storage spot; they will last a month or more. Avoid the temptation to refrigerate them, as they acquire an off flavour and often become hard in the centre. Once a sweet potato starts to go bad, it’s not simply a matter of cutting out the bad piece and using the remainder – the bad taste permeates the whole vegetable.
Peel sweet potatoes right before you cook them to avoid oxidization. They adapt wonderfully to different flavours and cuisines – try them with lemongrass, ginger, Thai curry pastes or Middle Eastern spicing.
True yams are grown in Africa, South America and the Caribbean. They are starchier and drier than sweet potatoes and slightly higher in calories. Their ends are rounded, instead of tapered and their skin is brown and bark-like. They can grow very large. Yams can be roasted, boiled and fried, and are excellent in vegetarian stews.
Both yams and sweet potatoes are nutritious, tasty and adaptable to diets, as they are lower in calories than potatoes and flexible in what you can do with them.
Sweet potato fries are a favourite, but home cooks don’t want to deep-fry them because it is a hassle and increases the calorie count. I have made a credible baked sweet potato fry that tasted like the real thing. The secret is dusting them with cornstarch before baking.
Slice 2 or 3 sweet potatoes into thin strips as evenly as possible. (I like ¼-inch strips, but it is personal preference.) Toss them in a bowl with 2 tbsp olive oil. Salt them then dust with 1 tbsp cornstarch. Place on a parchment-lined baking sheet in a single layer and bake for about 25 to 30 minutes at 425 F, or until browned and crispy, turning them once halfway through. They are crispier if you do not use parchment paper, but the cleanup is harder. Season again with any kind of herbs and spices you enjoy. Delicious and nutritious.
Need some advice about kitchen life and entertaining? Send your questions to lwaverman@globeandmail.com.
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Lucy Waverman