The Inscrutable Sweet Potato
By Dani Lind | Photos By Jim Klousia 0
To vegetable nerds like me, the history, folklore, nutrition and culinary potential of produce fascinate like nothing else. Everyone eats; we have always eaten—hence, agricultural development goes hand in hand with human development. Vegetables are so vibrant and nourishing and interesting, each one with a unique story.
This is the alluring tale of the Sweet Potato, a humble vegetable at first glance, but dig a bit deeper and you’ll find it has more character than the average tuber.
I (Y)am a Sweet Potato
The difference between a sweet potato and a yam is a mystery to most Americans. The sweet potato (Ipomoea batatas) is neither a yam (Dioscoreae genus, native to Africa) nor a potato (Solanum tuberosum, native to Peru). A member of the morning glory family native to tropical Central and South America, the sweet potato grows tuberous roots below a mass of flowering vines. It is one of the oldest vegetables known to man—traces of 10,000-year-old wild sweet potatoes have been found in Peruvian caves, and they've been cultivated by native South Americans for at least 5,000 years. Today, there are over 400 varieties of sweet potato grown around the world, varying in color from white to yellow, orange, red and purple. African yams, on the other hand, are bigger, heavier, starchier, generally white-fleshed and grow above ground.
The confusion between the two started in the U.S. in the middle of the last century. The common varieties of American sweet potatoes at that time were white-fleshed, so when a new variety of orange-fleshed sweet potato was introduced, the name "yam" was commercially applied in order to distinguish it from the others (even though yams are usually white-fleshed). The misnomer has continued to this day. Orange varieties have become ubiquitous and are still called yams, even though they are sweet potatoes, botanically.
Christopher Columbus first brought sweet potatoes back to Europe from the Americas in 1492, and from there they quickly spread to Africa, India, Southeast Asia and the Philippines. Yet when Europeans first made it to Polynesia in 1595, sweet potatoes genetically originating from Peru had already been a staple food there for hundreds of years—1,000- year-old carbonized remains have been found in the Cook Islands. Enter the greatest puzzle surrounding the sweet potato. How the heck did it get there?
Ancient Polynesians, originating from somewhere in Southeast Asia, had been blithely colonizing the Pacific islands between Hawaii, Easter Island, and New Zealand by boat for 2,500 years, bringing crops with them.When Europeans first encountered Polynesians, the only crop they cultivated not of Asian origin was the sweet potato. Scientists agree that those sweet potatoes must have come from Peru, but no one can agree on how they got there.
Seed pods, transplants or rooted slips could not have made the 5,000-mile trip over open water from Peru to Polynesia without the intervention of humans. Did these veteran sea-navigators float to South America and back, returning only with a load of sweet potatoes as evidence? Or did Peruvians make the long journey west, even though they customarily stuck close to shore? Neither is likely, as no records of human contact exist between the two cultures back that far. In theory, a raft loaded with roots could have accidentally drifted out to open sea un-manned and made its way to the Islands; but the native Peruvian word for sweet potato, kumal, and the Polynesian one, kumala, certainly imply human contact. Thus has this unassuming vegetable sparked heated debate for archeologists, anthropologists and botanists worldwide.
Returning the story to North America, as Europeans colonized the Southeast they cultivated sweet potatoes in earnest. Easy to grow and store in warm climates and full of important nutrients, the sweet potato became an extremely important source of nourishment in the Southeast during the Revolutionary and Civil Wars, and especially during times of famine. Confederates even used dried and roasted sweet potatoes as a coffee substitute in a pinch. Despite being an integral part of Southern food culture, the sweet potato’s popularity has declined over the last half-century from over 30 pounds per person per year in 1920 to less than four pounds today, perhaps due to its association as a hard-times food.
Reaping the Benefits
Now is the time to enjoy locally grown sweet potatoes. You can find them at farmers markets and local produce stores from September through November (the rest of the year they tend to come from California). It's a bit tricky to grow sweet potatoes here in the northern Midwest, but with care it is possible to grow them successfully. They take 90 to 150 days to mature and do not tolerate frost or cool nights. Northern growers plant shorter season varieties late in the season (well into June), cover with floating row cover during their infancy, and often employ black plastic mulch to emulate the warm climates where they thrive. Proper curing after harvest requires steady warmth and humidity for a couple of weeks to develop sweetness and harden the skin for storage; although, even stored properly they keep well for only a few months.
Sweet potatoes are high in complex carbohydrates, fiber, beta carotene (which our bodies turn into vitamin A), vitamins C and B6, and have significant amounts of potassium and iron. They can help diabetics with insulin resistance and blood sugar level stabilization. Their antioxidant content is three times more concentrated in the skin than the flesh, so buy organic and eat the skins.
They should be stored in a dark, cool place (55 to 65 degrees) loose or in paper bags—never in plastic or the fridge. Sweet or savory, they can be baked, roasted, steamed, boiled, simmered or fried. They can even be grilled whole over hot coals, a popular street food in China, Korea and Japan.
Obviously, the sweet potato is a nutritional powerhouse teeming with culinary possibilities. The mystery I really want to solve is why most people limit it to marshmallow casserole at Thanksgiving! If your sweet potato repertoire is limited, get to the farmers market and try out one of these ideas:
- Bake or grill whole at 350 degrees for 35 to 45 minutes, choosing similarly sized roots for uniform cooking. Dip in a sauce of tamari, mirin, sugar, rice vinegar, ginger and scallions. Or split open and douse with butter and chives.
- Bake extra to add to breads, biscuits, pies and cakes, or freeze for later use.
- Simmer peeled and cubed sweet potatoes in soup, chili, or Thai, Indian or Indonesian coconut curries.
- Combine with other cubed or sliced root vegetables, toss with olive oil and roast with garlic and fresh herbs.
- Cut into fries, toss with oil, salt and chipotle powder and roast on a cookie sheet for oven fries.
- Boil with potatoes and serve mashed.
Go beyond marshmallow casserole with one of these incredible sweet potato recipes, which accompanied this article in the Fall 2010 issue:
Curried Sweet Potato Bisque
Savory Sweet Potato Pancakes