Stop Settling for Bland Sweet Potatoes—This Simple Step Makes Them Taste Even Sweeter

Whether you like your sweet potatoes mashed and plush or roasted until their edges turn sticky and caramelized, you've probably noticed that even within the same preparation, they don't always taste equally sweet. Some batches come out rich and candy-like; others are flat and starchy. That swing isn't random, and it has nothing to do with adding sweeteners like honey or sugar to a recipe. It comes down to how you cook the sweet potatoes.

Below, I look at the simple but game-changing science behind sweet potatoes' natural sweetness—specifically, the temperature window where an enzyme inside the potato converts starches into the sugar maltose. Understanding that range, and how to keep sweet potatoes in it long enough, is the key to getting consistently sweeter, more flavorful results—whether you're serving them roasted or slow-roasting them first before using them in another preparation, like mashed potatoes or dip. Here, I break down how the process works, why it matters, and the most reliable home-cooking methods to maximize sweet potatoes' full potential.

Sweet Potatoes vs. Yams

Before we get into the science, it's worth noting that the "yams" in most US supermarkets are really just orange-fleshed sweet potatoes. True yams are a different root altogether—dry, starchy, and not nearly as sweet—and they're usually only found in African, Caribbean, or some Asian markets. In this article, I'm strictly talking about sweet potatoes.

The Science Behind Perfectly Roasted Sweet Potatoes

If you've ever wondered why some sweet potatoes taste deeply sweet while others come out bland and starchy, it depends on what happens to the potato's starch as it heats. Sweet potatoes contain a naturally occurring amylase enzyme that can convert starch into maltose, a sugar that contributes to their natural sweetness. But this conversion only happens if the potato spends enough time within a specific internal temperature range. As Harold McGee writes in his seminal food science book On Food and Cooking:

"Moist sweet potato varieties sweeten during cooking thanks to the action of an enzyme that attacks starch and breaks it down. The enzyme starts to make maltose when the tightly packed starch granules absorb moisture and expand, beginning at around 135°F, and it stops when the rising heat denatures it, at around 170°F."

Here's what that means in practice:

• As the sweet potato heats, its tightly packed starch granules begin to swell and absorb water.
• Once they reach about 135°F (57°C), the amylase enzyme becomes active and starts breaking those starch molecules into maltose.
• This reaction continues until the potato reaches about 170°F (77°C).
• Above that point, the enzyme denatures—its structure unravels—and the reaction stops entirely.

The key to getting a sweeter sweet potato is maximizing the time it spends in that 135°F to 170°F window. The longer the potato's interior stays there, the more starch gets converted into maltose and the sweeter it becomes. If the potato moves past this range too quickly—as it easily can in a hot oven—the enzyme barely has a chance to work, and the potato tastes more starchy than sweet.

This starch-to-maltose conversion also explains differences in browning. Maltose caramelizes more readily than raw starch, so sweet potatoes that spend more time in the enzymatic zone brown better and develop deeper flavor during roasting. Potatoes that skip through it quickly often look paler and taste flat.

It's worth noting that true yams don't do this, and although some winter squashes—such as butternut, kabocha, and Hubbard—have mild amylase activity that can create a little extra sweetness as they warm, the effect is subtle. Sweet potatoes are by far the most pronounced example.

How to Get Perfectly Roasted Whole Sweet Potatoes

For whole sweet potatoes with deeper sweetness and a creamy interior, this is the method to use.

• Choose the right variety. Use moist, orange-fleshed sweet potatoes like Garnet, Jewel, or Beauregard for the best sweetness and texture.
• Wrap tightly in foil. Seal unpeeled, whole potatoes in heavy-duty foil (add herbs, such as thyme and rosemary, if you like). The enclosed moisture keeps the potatoes heating gradually, giving the enzyme time to convert starch into maltose.
• Start in a cold oven set to 300°F (150°C). Start with the oven off. Place the foil-wrapped sweet potatoes on a rimmed baking sheet, transfer to the oven, then turn the oven on to 300°F. This slow warm-up maximizes the time the potatoes spend between 135°F and 170°F, where most of the sweetness develops. Roast until a skewer meets some resistance, about 1 hour and a half to an hour and 45 minutes.
• Unwrap and increase the heat. Remove the foil, discard (or compost) any herbs, and place the potatoes directly on the baking sheet. Increase the oven to 400°F (205°C) and roast for about 30 minutes, until deeply caramelized and completely tender.

Cool slightly, then use as you like. Let them cool until they're easy to handle. Peel and mash with butter and seasonings for mashed potatoes, or split and fill them with beans, cheese, sour cream, or whatever you like for stuffed baked potatoes.

How to Get Perfectly Roasted Sweet Potato Pieces

If you want roasted sweet potato pieces—with deeply browned sides and crisp edges—roasting them whole won't get you there. The method outlined below builds in the same sweetness-boosting step while still giving you the texture you want.

• Cut them into even pieces. Leave skins on or peel, then cut sweet potatoes into 1/2-inch slices or cubes so they heat evenly and brown at the same rate.
• Hold them in hot water first. Place the pieces in a saucepan, cover with water, and heat to 160°F (71°C). Turn off the heat, cover the pot, and let the sweet potatoes sit for about 1 hour. This keeps them in the 135°F to 170°F range where starch converts into maltose.
• Toss with oil/butter and seasonings. Drain well, then toss with olive oil or butter, salt, and whatever seasoning you like—black pepper, Aleppo pepper, smoked paprika, or a mixture. Coating the pieces evenly in fat helps them brown more deeply in the oven.
• Spread them out for roasting. Arrange in a single layer on baking sheets so they roast instead of steam.
• Roast at a hot temperature for color and texture. Roast at 400°F (200°C) until the bottoms brown, about 30 minutes. Flip and roast another 20 minutes, until tender and caramelized.
• Finish while warm. Toss with a little more olive oil or cold butter (cold butter emulsifies instead of turning greasy), fresh herbs, and a drizzle of honey or maple syrup for added sweetness, if desired.

Whether you enjoy sweet potatoes in savory dishes or in desserts like pie or cheesecake—or see them as living in both realms at once (looking at you, sweet potato casserole)—they're at their best when their natural sweetness has time to develop. As autumn and winter cooking settle in, give these roots slow, steady heat that pays off in deeper flavor.