Surprising Facts About the Humble Sweet Potato and Yam

Thanksgiving dinner image from the Rochester YMCA

Happy Thanksgiving, everyone! As we take the day to count our blessings, I’m sure we will all be gobbling up plenty of turkey, green bean casserole, mashed potatoes, and more. There is one traditional Thanksgiving treat, though, that I think is far too under-appreciated: the humble sweet potato. Or yam, if you prefer. It’s certainly one of my favorite Thanksgiving dishes, and not just because it goes so well with brown sugar and marshmallows.┬áIt’s also because the sweet potato, out of all the foods on your table today, has by far the most fascinating history.

For one thing, sweet potatoes and yams are not the same thing. While American cooks treat them roughly the same way and we use the two terms interchangeably, in fact the sweet potato and the yam are two very different plants with two very different origins. Both are tubers that are grown in the ground, just like potatoes, but they belong to completely different plant families. Yams are actually a group of similar plants native to Africa and Asia, while sweet potatoes are native to Central and South America and are a part of the same plant family as Morning Glory flowers.

Here's a Sweet Potato plant's flower...

Here’s a Sweet Potato plant’s flower…

...and a Morning Glory. See the similarities?

…and a Morning Glory. See the similarities?

Sweet potatoes tend to have smooth skins, moist textures, and naturally sweet tastes. Yams tend to have rough skins, dry textures, and starchy flavors. Another key difference is that yams will make you sick if you eat them raw – they have to be cooked to break down some slightly toxic chemicals in the raw root.

So why the confusion? Slavery is the culprit. African slaves who were brought to the New World thought some sweet potato varieties sort of resembled the yams they were used to back home, and the name stuck. Today, in order to reduce confusion, the U.S. government requires that if sweet potatoes are labelled as “Yams”, they must also be labelled as “Sweet Potatoes”. Actually, now that I think about it, wouldn’t that just make things more confusing?

In any case, sweet potatoes have been cultivated in the Americas since at least 3,000 BC, and possibly earlier. There are records of its cultivation by Native American farmers from Louisiana to Peru. Most interestingly, however, archaeologists have discovered that sweet potatoes were cultivated in Polynesia as early as 1000 AD – long before Christopher Columbus’s voyage! How did they get there?

Gee, I wonder.

Gee, I wonder.

Well, Polynesians were a well-known maritime civilization. After all, they had to sail from island to island to colonize the Pacific. They certainly had the technology to reach the Americas. Not only that, but it would have been theoretically possible for South Americans to reach Polynesia as well. In 1947, Norwegian adventurer Thor Heyerdahl and five partners built a boat using materials and technologies that would have been widely available in ancient Peru, named the boat the Kon-Tiki, and set sail for Polynesia. It took them 101 days, but they made it, showing that such a voyage would have been theoretically possible. This feat has been replicated numerous times since then. Perhaps the sweet potato’s journey across the Pacific is proof that Columbus’s voyage wasn’t so unique after all.

"I could have told you that." -Leif Ericson

“I could have told you that.” -Leif Ericson

Whatever the truth is, we do know that sweet potatoes were an essential part of Colonial Americans’ diets, and as recently as the Civil War most large farms and plantations had dedicated areas to store the plants under a pile of straw to keep them warm during the winter. It was also during the Civil War, when shortages of coffee were frequent, that dried, ground sweet potatoes were brewed for that morning jolt instead.

If you think that’s strange, consider that in many parts of Asia and Latin America, they have found all manner of ways to serve sweet potatoes besides brown sugar and marshmallows. In southern China, Sweet Potato Soup is a common dessert; in the Philippines, it is sometimes served with fish sauce; and in South America, it is mixed with chocolate, jellied, and served as Dulce de Batata. The Japanese have even made sweet potato wines!

Pictured: Sweet potatoes.

Pictured: Sweet potatoes.

This Thanksgiving, when you sit down with your family to enjoy each others’ company, give a little more respect to that pot of sweet potatoes or yams. It may not be the main course, but it certainly has far more to it than meets the tongue.