- Creamy, moist, deeply flavorful flesh
- Fastest possible method
- No burnt sugar on the bottom
Though they share a name, white potatoes and sweet potatoes couldn’t be more different. The most familiar sweet potato varieties in American supermarkets, which have rusty orange or red-purple skin and deep orange flesh, come from a different botanical family than white potatoes such as russets and contain far less starch and more sugar. As a result, they cook very differently—a fact that is never more apparent than when preparing a simple baked potato.
Not long ago, we discovered that baking a russet potato in a 450-degree oven for about 45 minutes produced an ideally fluffy interior (see our complete findings at work in our Best Baked Potatoes recipe). But when I followed the same approach using a sweet potato, the interior was dense and watery. Meanwhile, I tried a handful of baked sweet potato recipes and came upon one from chef Michael Solomonov of Philadelphia’s Zahav restaurant that revealed how truly extraordinary a baked sweet potato can be. After the spuds had spent about 3 hours in a 275-degree oven, their interiors were not just tender but downright plush, and their flavor was concentrated to the point of tasting caramelized, with hints of molasses. These were unlike any sweet potatoes I’d ever eaten.
But tying up my oven for 3 hours when I wanted to bake sweet potatoes wasn’t an option. My aim was to expedite the process (about an hour seemed reasonable) without compromising the exceptional flavor and texture the potatoes got from the longer method.
Sweet potatoes look, taste, and cook differently from white potatoes because they’re from different botanical families. Sweet potatoes are members of the Convolvulaceae family, which includes plants with fleshy storage roots, such as morning glories, while white-fleshed potatoes belong to the Solanaceae (or nightshade) family. Their nutrient makeups—including their starch and sugar contents—also differ.
The difference in starch content between russet potatoes and orange-fleshed sweet potatoes (the kind that I’ll refer to throughout this story) is actually twofold: First, russets contain roughly 21 percent starch versus 15 percent in sweet potatoes. That 6-percent gap is significant because starch absorbs free moisture in the potato as it cooks, so a russet ends up with a drier texture after baking. Second, the starch granules in russets are almost twice as big as those in sweet potatoes; when they swell with water, they eventually force the cells to separate into distinct clumps that result in a texture we perceive as dry. Sweet potatoes have fewer and finer starch granules, so they absorb less water and thus bake up soft and creamy instead of dry.
My question was, when does a baked sweet potato reach the stage when it turns soft and creamy throughout? Per the Zahav approach, I baked three 8-ounce sweet potatoes in a 275-degree oven (I set them on a wire rack in an aluminum foil–lined rimmed baking sheet, knowing that they tend to ooze sugar during baking) and pulled one out every hour to check its temperature and consistency. As expected, the longer a potato cooked, the higher its temperature rose and the more uniformly soft it became. The potato pulled at 1 hour reached about 180 degrees, the 2-hour potato reached about 190 degrees, and the 3-hour potato reached about 200 degrees. Only the potato that cooked for the full 3 hours boasted the creamy, soft consistency and caramelized sweetness I wanted.
Could this mean that all I had to do was figure out the fastest way to get the potatoes to 200 degrees? No, because baking them in a 450-degree oven until they hit 200 degrees, which took about 45 minutes, would bring me back to my original problem: a barely tender, watery core.
Clearly, there was a benefit to baking the potatoes longer, so I put another set of potatoes in a 275-degree oven to take a closer look. This time I weighed the potatoes before and after baking to track moisture loss, which I assumed would correspond to flavor concentration, and inserted probes into each potato so that I could monitor its progress. As I recorded temperatures every 10 minutes, I noticed that the potatoes reached 200 degrees shortly after the 2-hour mark, meaning they spent almost the entire last hour at that temperature. They also lost an average of about 30 percent of their starting weight—about twice as much as the potatoes baked quickly in the 450-degree oven, I later discovered—and boasted a creamy consistency with complex flavor. But why?
Our science editor explained that when a sweet potato approaches 200 degrees, the pectin that gives its cell walls structure begins to break down so that the flesh softens and allows free moisture to escape. At the same time, starch granules within the cell walls take up free water and gelatinize, which makes the potato appear smooth and creamy. But it turns out that at 200 degrees and up to about 212 degrees, the pectin breakdown becomes more rapid, leading to greater softening. It also leads to moisture loss, which causes the spud’s sugars to both concentrate and caramelize, leading to more-complex flavor. And the longer the potatoes hover in that 200-plus zone, the creamier and more flavorful they become.
Producing baked sweet potatoes with creamy, deeply flavorful interiors isn’t just about cooking the spuds to a particular temperature (200 degrees or so). At that point, they’re barely tender, chunky, and still full of water that dilutes their flavor. You have to hold them at that temperature for an hour, which allows time for cell walls to break down, starches to gelatinize, and moisture to evaporate so that flavor concentrates.
Now that I understood why the potatoes needed that extra hour at 200-plus degrees, I wondered if I could shortcut the front end of cooking by getting the potatoes to 200 degrees as quickly as possible and then let them linger in the oven. I baked the next batches in ovens set to 400, 425, and 450 degrees, weighing the potatoes before and after and probing them as I had before. Baked at 450, the potatoes reached 200 degrees in about 35 minutes. But after another hour in the oven, they had nearly burned on the outside. When baked any lower, they still took almost 2 hours to turn creamy and deeply flavorful—too long for a simple side.
There was one approach I hadn’t yet tried: microwaving the potatoes until they hit 200 degrees and then finishing them in the oven. I was skeptical, since when we developed the baked russet recipe, we found that microwaving the spuds turned the flesh gummy. That’s because their large and abundant starch granules are relatively fragile, and heating them rapidly in the microwave made them burst and release starch, which created a texture that we perceive as gluey.
But since sweet potatoes contain fewer and finer starch granules, I gave it a shot. I microwaved them until they had reached approximately 200 degrees at their cores, which took less than 10 minutes. Then I transferred them to a 425-degree oven—the hottest temperature I could use without burning them—to bake for a full hour. This hybrid cooking method did the trick: Their texture was creamy, almost fudgy; their flavor, complex and sweet; and their skin nicely tanned but not burnt. Best of all, barely more than an hour had passed, and they tasted just as good as the 3-hour version.
In fact, my sweet potatoes were so moist and creamy that they didn’t need any butter or toppings, though I couldn’t resist putting together a couple of simple ones to dress them up (yes, they’re company-worthy). The first was an Indian-spiced yogurt; the second, a garlicky sour cream laced with chives.
To produce potatoes with silky, deeply sweet flesh, we needed to bake them for about an hour after they reached 200 degrees. The question was, how fast could we get this done?
Creamy, moist, deeply flavorful flesh
Microwaving the potatoes to 200 degrees and then baking them for another hour causes their cell walls to break down and their starches to gelatinize, yielding a smooth, plush texture. Much of their moisture also evaporates during that time, so their flavor concentrates.
Fastest possible method
Parcooking the potatoes in the microwave speeds the initial cooking stage so they can spend a full hour in the oven, where evaporation and flavor concentration take place.
No burnt sugar on the bottom
Baking the potatoes on a wire rack set in a foil-lined baking sheet helps air circulate around them; the sheet also catches any sugary syrup that inevitably oozes from the potatoes as they cook.