Why It Works
- Cooking the sweet potatoes in the oven from start to finish simplifies the recipe compared to many others.
- Starting in a cold oven gives the sweet potatoes more cooking time at a lower temperature, helping to more effectively break down their natural starches into simple sugars.
- A higher proportion of water in the syrup ensures that the sugar dissolves properly, and prevents the syrup from breaking into a greasy pool later.
- Cider vinegar and powdered ginger add subtle tartness and a warm heat that keep the dish's sweetness in balance.
Oversweetened sweet potatoes get a lot of flak. If you don't believe me, go take a look at the comments on my article about marshmallow-topped sweet potato casserole. A glutton for punishment, I will wade into this controversial zone again, this time with the classic Southern dish of candied yams, which are not yams at all but sweet potatoes...in an intensely sweet sugar sauce.
I don't have much of a sweet tooth, but even I don't fully understand the hate toward these dishes. Yes, as stand-alone creations, they're super sweet. But they're not meant to be eaten on their own. Particularly popular as part of the Thanksgiving table, these are foods that are intended to be served in small doses alongside a variety of other foods that are savory, tart, and rich. Just as I wouldn't want to drink a glass of maple syrup, but still love it on pancakes, extra-sweet sweet potato dishes can work when they're a small part of a larger, more complex, and balanced whole.
Candied yams are, on their face, very simple: sweet potatoes cooked with a spiced and buttery syrup. The funny thing is that despite this overall simplicity—after all, the only components are the sweet potatoes and the syrup—my testing led me to deviate from almost every other version of this recipe I've seen. I'm convinced the changes I made result in a superior version of candied yams, ones that are silky and tender, flavorful, and coated in a shiny shellac of syrup. They're also more balanced in flavor, thanks to some cider vinegar that I sneak into the sauce for a pinpoint of tartness, which helps to pull all that sweetness into focus.
These incredibly sweet sweet potato dishes don't have to be cloying; they just need to be made more thoughtfully.
Do You Need to Par-Cook Sweet Potatoes for Candied Yams?
Let's start with the most basic fact about this dish: Although they're commonly described as "yams," which are native to Africa and Asia, the tuber in question here is actually the sweet potato, native to the Americas. We could be more accurate and call these "candied sweet potatoes," and many people do, but "yams" still appears to be the more frequent term used (at least according to Google search data).
Most recipes begin with par-cooking the sweet potatoes before combining them with the syrup and finishing them in the oven, so that's where I began my testing. I baked the sweet potatoes whole, and I simmered them both whole (with and without their skins) and precut.
Baking didn't work well, since gauging the doneness of the sweet potatoes was difficult, and the potential to accidentally cook them until they're over-soft is high.
The simmered sweet potatoes showed marked differences straight out of the water: The skin-on whole sweet potatoes had the most flavor, while the pre-peeled, presliced ones had the least, as they lost it to the water. But, once the sweet potatoes were combined with the sugar syrup and baked, the differences disappeared.
I also played with both low- and high-temp par-cooking approaches, since we know that holding sweet potatoes at relatively low heat—between 135 and 170°F (57 and 77°C)—allows enzymes to more fully break down their starches into simple sugars. Once again, whatever was gained by using that method was overshadowed once the syrup was added.
Eventually, I began to question the par-cooking step as a whole. Why, exactly, was everyone doing it? I ran a couple test batches in which I cooked the sweet potatoes from start to finish in the oven, first covered with foil until tender, then uncovered to finish. They came out better than any of the ones I made using the par-cooking approach so common to other recipes. That's great news, because it's a much easier recipe when you don't have a two-step cooking process for the sweet potatoes.
Making a Proper Sugar Syrup
The other part of this sweet-on-sweet equation is the syrup. I started where most classic recipes do, melting sugar with a few tablespoons of water plus butter, then pouring that mixture over the potatoes. For the sugar component, I tested both granulated white sugar and light brown sugar, and there's not much of a contest. The molasses in light brown sugar adds a depth of flavor and hint of bitterness that plain white sugar can't hope to match. Given the sweetness of this dish, any layers we can add beyond merely more sweetness are welcome.
Early on, though, I started running into trouble. My sugar syrup always looked good in the saucepan, but once combined with the potatoes and baked in the oven, it always ended up breaking into a thin and greasy soup, with the sugar forming a thick layer of caramel stuck to the bottom of the baking dish. From what I could tell by looking at online photos of other renditions of the dish, this was a problem a lot of people were having. For some reason, they seemed to think this was an acceptable outcome. It's not. If we wanted greasy baked sweet potatoes in caramel glue, that's what we'd call the dish. But these are supposed to be candied yams, and that, to me, suggests tender pieces of potato in a glossy lacquer of rich and buttery candied syrup.
I suspected that I needed to increase the amount of water in my sugar syrup, but I also knew that I work with pastry wizard Stella Parks, who's far more knowledgeable about candy syrups than I am. She could help get me to a good answer a lot faster than I could merely through trial and error. So I asked her—what gives, and do you think more water will fix this?
Stella came back with some information: The problem with the amount of water I had been using, and the amount of water in most candied-yam recipes, was that it was insufficient to completely dissolve the sugar. The syrup was never properly forming in the first place, even though all appearances in the saucepan said otherwise. Because there wasn't enough water, and therefore there wasn't a true syrup, the sauce was on the verge of falling apart the first chance it got, which was exactly what was happening in the oven.
The solution is to start with significantly more water, about three times as much, to fully dissolve the sugar. After that, cook the syrup beyond 212°F, to about 220°F (104°C) or so, to drive off the excess water and create a true syrup—one that won't separate from the fat with longer cooking.
Sure enough, with that simple adjustment, the syrup came together, and stayed together, beautifully.
With that resolved, it was time for my final move: adjusting the flavor of the syrup to keep the sweetness in check. In my marshmallow-topped sweet potato casserole recipe, I did that by adding sour cream and fresh ginger to the mashed-potato mixture, ingredients that add tang and pungency to balance out all the sugar. Here, I use a similar approach, but slightly different ingredients. On top of a classic blend of warm cinnamon and allspice, I add a large pinch of ground ginger for a hint of spiciness, and I spike the syrup with cider vinegar. The vinegar pairs really well with the other flavors in the dish, while adding a subtle sweet-and-sour effect that keeps the syrup from straying into sickly-sweet territory.
- 2 1/2 pounds (1.1kg) sweet potatoes, peeled and sliced crosswise into 1/2-inch-thick rounds
- 1 cup light brown sugar (about 7 ounces, lightly packed; 200g)
- 1/4 cup unsalted butter (2 ounces; 60g)
- 1/2 cup (120ml) water
- 1 tablespoon (12g) Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
- 1 tablespoon (15ml) apple cider vinegar
- 1/8 teaspoon ground cinnamon
- 1/8 teaspoon ground allspice
- 1/8 teaspoon ground ginger
In a 9- by 13-inch baking dish, arrange sweet potato rounds in an even layer, overlapping where necessary to fit them all. Set aside.
In a small saucepan, combine brown sugar, butter, water, and salt and bring to a boil, stirring often, until syrup registers 220°F (104°C) on an instant-read thermometer. Stir in cider vinegar, cinnamon, allspice, and ginger, then pour syrup all over sweet potatoes, spooning it over them as necessary to wet them completely.
Cover baking dish with aluminum foil and place in a cold oven. Turn on oven to 250°F (120°C) and allow it to come up to temperature. Cook, stopping to flip and baste sweet potatoes with syrup every 20 minutes, until tender throughout, about 1 hour 15 minutes. (Exact cooking time will depend on your oven, baking dish, and the size of your sweet potatoes, so check frequently.)
Remove foil and continue to cook, flipping and basting sweet potatoes occasionally, until they are very soft and glazed in a rich brown syrup, about 30 minutes longer. Let cool slightly, then serve.