What’s the Actual Difference Between Yams and Sweet Potatoes?

Knobbly and brown, with little, wispy, hair-like roots shooting off at random, yams aren’t the stateliest of foods. But if you get past their slightly odd appearance, you may very well fall in love. That is, if you even cross paths with a real yam. Chances are, unless you’re doing most of your grocery shopping at African, Caribbean, or Asian markets, or grew up eating and cooking these tubers, what you imagine when I say “yam” is actually just an orange sweet potato.

As I dug into just a little bit in my field guide to sweet potatoes—way too many puns here, I know—the practice of calling sweet potatoes yams started in the early 20th-century, when Southern farmers introduced softer-fleshed orange sweet potatoes to the American market. Farmers called orange tubers yams to differentiate them from the white-fleshed sweet potatoes people were already familiar with. The name stuck, and all these years later a good portion of us still couldn’t point out a real yam in a lineup. And that’s a shame, because their flavor and texture are completely unique, and they take well to all sorts of cooking methods and seasonings. A true yam is much starchier than a sweet potato, with a milder sweetness that becomes only slightly more pronounced when the root is cooked.

The History of the Sweet Potato-Yam Confusion

Calling sweet potatoes yams in America wasn’t just a money-making ploy. For the first enslaved West Africans forcibly brought to America, sweet potatoes offered as close to a taste of home as they were going to get. Though sweeter and more watery when cooked, these orange sweet potatoes resembled the yams of Africa both in texture and appearance. “Slavers transporting captives from [West Africa] on the Middle Passage provisioned themselves with yams sufficient for the voyages,” wrote culinary historian Jessica B. Harris in an op-ed on the cultural significance of the yam. “But once ashore in more temperate America, the slaves found that the African tuber was unavailable, and thus substituted it with the sweet potato—leading to centuries of botanical and gastronomic confusion.”

Really, yams aren’t remotely similar to sweet potatoes. They belong to the Dioscoreaceae family of flowering plants, and grow in temperate and tropical climates, including in Africa, Asia, and the Caribbean. A yam is the extremely starchy tuber at the base of winding, bright-green herbaceous vines. While sweet potatoes generally don’t grow much longer or thicker than a baby’s forearm, yams can grow to be more than six feet long, and on rare occasions weigh in at over 150 pounds. That’s a very, very big tuber, and needless to say, not the sort of produce you’ll find squeezed into a grocery bin. There are more than 800 varieties of yams, and a majority of those are cultivated in Africa, with Nigerian farmers producing more than half of the world’s supply.

Some of the most common yam varieties you’ll come across include the popular white and yellow yams native to Africa, which resemble large potatoes in shape. In Asian markets you’ll find Chinese and Japanese yams, which have lighter-brown skin, and are cylindrical. Because yams are grown and eaten in different parts of the world, methods for cooking vary enormously from one kitchen to the next.

How to Buy and Cook Yams

Yams are very resilient, and they travel well. This means that, for the most part, you don’t have to worry about accidentally picking up a yam at the store that’s already spoiled—unlike the cursed-but-seemingly-fine avocado that is always rotten in the middle, no matter how beautiful its exterior is. If a yam’s skin is intact, and the root doesn’t have any soft or mushy spots, consider it good to go.

In Jamaica, you’ll find yams slowly roasting, skin still on, over an open fire. When they’re done, the interior can be easily pierced with a knife, but the skin isn’t burnt—an impressive feat. The meaty flesh of the yam, slightly smoky from the fire, is served alongside flavorful chunks of jerk pork, chicken, and other meats.

In Nigeria, where so many of the world’s yams are grown and the tuber is central to everyday life, they’re cooked into porridges, and cubed and stewed slowly with tomatoes, peanuts, greens, and spices. They’re also boiled then pounded into a version of fufu, one of West Africa’s most iconic dishes. The doughy, starchy mixture is perfect for absorbing sauce, and is eaten alongside more or less everything.

The yams eaten in the Caribbean and throughout Africa are larger and more bulbous than Chinese yams, which are also known as nagaimo in Japan. In China, the yams are sliced into rounds and boiled in soup until tender, stir-fried with fresh vegetables, blended into savory steamed cakes, and more. You can find wild Chinese yams pre-sliced and sun-dried in Chinese grocery stores. The dried yams, pictured above, are known as huai shan, and cooks reconstitute them in rich broths, simmering along with chicken, pork, goji berries, and dried jujubes.

Chinese and Chinese-American cooks like Lisa Lin, a food blogger and expert on Chinese cooking, also utilize a yam called yamaimo or East Asian mountain yam. This variety has a sticky, slightly slippery texture, and is often sliced finely and eaten raw. “One way to prepare the yams is to boil them in a soup,” says Lin. “My mom (the kitchen matriarch) says that the best ones for boiling are smaller ones or the ones that look very twisted and crooked—usually found in farmers’ markets. They don’t break down and turn to mush when they’re boiled.”

In Japan, among other applications, the starchy nagaimo and yamaimo yams are grated into the batter of okonomiyaki—chewy, savory pancakes showered in toppings and a mixture of a sweet and savory sauce and mayonnaise. The starchiness of the grated yams helps bind the pancake batter together, without adding too much moisture.

I’ve only touched on the very tip of the yam-shaped iceberg. There are hundreds of varieties of yams out there, used in more culturally diverse preparations than I could count. The knobbly root takes well to frying, braising, sautéing, boiling, roasting, and more. You just have to decide where to start.

October 2019