There are times when it's important to memorize the distinction between two similar-seeming items: A home cook who uses baking soda instead of baking powder won't produce an award-winning cake, and the dry-aged steak lover who buys a wet-aged steak will end up wondering why the meat tastes so funky. Even though cooks use yams and sweet potatoes interchangeably, you're unlikely to find a true blue yam at a grocery store, farmers' market, or restaurant in this country. Here's what makes these two so distinct.
Sweet Potatoes vs. Yams
With exceptionally rare exceptions, every orange-fleshed tuber you see or taste in the U.S. – even those sold as candied yams – is a sweet potato. Yams and sweet potatoes aren't even botanical kin. Yams are dry, starchy root vegetables, closer in flavor to yucca than the sweet potatoes you bake with marshmallows or roast for a kale salad. They originated in Asia and Africa, which is how the confusion began.
When Southern farms started cultivating soft sweet potatoes, as opposed to firm sweet potatoes, for commercial sale, enslaved laborers assigned the new crop an African nickname. In parts of Africa, yams are known as "nyami." The mix-up was compounded in the 1900s when sweet potato sellers started promoting red-skinned sweet potatoes as yams. Because yams are typically only sold in specialty stores that serve African communities (Africa produces 95 percent of the world's yams), you don't have to worry about whether yams are an appropriate substitute for sweet potatoes. Nor are you likely to find many English language recipes for true yams.
Taste the Difference
Sweet potatoes, native to the Americas, are another story. There is tremendous diversity in the sweet potato sector, and growers are constantly adding more heirloom varieties to the mix. You can find sugary sweet potatoes with snow-white flesh, and purple-fleshed sweet potatoes that taste like nuts. With hundreds of sweet potatoes to explore, finding the variety you like best is part of the fun. Still, there are a few varieties you're most likely to come across at the grocery store. The sweet potato that most Americans would classify as standard is a Covington, Beauregard, Garnet, or Jewel: It's orange on the inside, mildly sweet and moist.
Sweet Potato Nutrition
In certain nutritional categories, a sweet potato is possibly the best thing you could eat. Its beta-carotene content is off the charts. Plus, a single medium sweet potato provides 90 percent of the vitamin A you need all day, and 35 percent of your Vitamin C allowance. Although it only contains 100 calories when baked, a sweet potato is rich in fiber, manganese, and antioxidants. Even its carbohydrates are complex, which means a sweet potato doesn't produce the energy bursts and dips associated with white bread and potato chips. You should probably be eating a sweet potato right now. Sweet potatoes are actually fairly similar to white potatoes in terms of calories and carbs. But sweet potatoes have a slight edge on fiber and really shine on vitamins A and C. They also tend to be more expensive than white potatoes.
Buying Sweet Potatoes
"Fresh" is typically a selling point when it comes to produce, but that's not the case with "freshly dug" sweet potatoes: You want potatoes that have been cured in a warm, humid place for a few weeks -- they taste better, because starches convert to sugars during that time. To find these, look for sweet potatoes that feel heavy for their size. Avoid bruises and soft spots; dirt on the potato is fine. And don't automatically buy the biggest sweet potato in the basket, since very big sweet potatoes are often stringy.
Storing Sweet Potatoes
Once the potato is in your own possession, store it in a dry, cool environment (such as your basement). Do not put a sweet potato in the refrigerator; that can change the way they taste. Correctly stored, a sweet potato ought to last one or two weeks.
Preparing Sweet Potatoes
Anything you do with regular potatoes, you can do with sweet potatoes.
- Boiling sweet potatoes: Bring a large pot of salted water to a boil. Add peeled, cubed potatoes and cook until tender, 20 to 30 minutes. Try turning them into mashed sweet potatoes.
- Baking sweet potatoes: To bake them in the microwave, pierce with a fork and cook for 5-8 minutes, rotating once). To bake in the oven, Preheat oven to 400°F. Pierce sweet potato with a fork about 6-8 times and place on a foil-lined baking sheet. Bake until tender, about 45-60 minutes. Try baking up some sweet potato fries.
- Roasting sweet potatoes: Preheat oven to 425 degrees F (220 degrees C). Drizzle olive oil over chopped, peeled sweet potatoes; pour into a shallow roasting pan. Roast, turning frequently, until soft and golden brown, 30-35 minutes. Try this recipe: Oven-Roasted Sweet Potatoes.
- Eat them raw: Sweet potatoes can even be eaten raw: Try grating them over a salad for a colorful garnish.
And just like white potatoes, sweet potatoes are edible inside and out; it's fine to eat the skin. The only prep that's required for all sweet potato recipes is a good scrub.
As Chef John's recipe proves, sweet potato casserole doesn't have to be cloying.