In 2022, I worked in the research and development lab at Audrey Restaurant in Nashville. Our owner-chef, Sean Brock, and his culinary team were deeply committed to supporting local farmers. When one of our farmers asked if we could find a use for 900 pounds of sweet potatoes he couldn’t sell, he cut us a deal, and we agreed to take them off his hands. That ended up being about 2,700 sweet potatoes! Many of those tubers made it into the prep kitchen for dinner service, but the remainder wound up in our lab to be experimented with and preserved in various forms, including misos, garums, amazakes and even sweet potato “chewies” made in the style of Japanese umeboshi. Needless to say, I learned a lot about sweet potatoes that fall.
First off, sweet potatoes are not potatoes. Potatoes are in the nightshade family, and sweet potatoes are in the morning glory family. Sweet potatoes are sometimes called “yams,” but they are totally unrelated. Sweet potatoes are starchy tubers and aren’t very sweet when tasted raw. Their sweetness comes from sweet potatoes’ ability to transform starch into sugars as they cook. This transformation is possible because sweet potatoes contain an enzyme called amylase, which converts flavorless starch molecules into maltose, a simple sugar with about one-third the sweetness of pure table sugar.
Starch is a polysaccharide, meaning it’s a big chain made of many smaller sugar molecules. Unless the starch is broken down into smaller sugar molecules, it won’t taste sweet. Our tongue simply doesn’t recognize it. When cooking sweet potatoes, the goal is to create conditions that allow the amylase enzyme to break down as many starch molecules as possible into sweet-tasting maltose.
In his book On Food and Cooking, Harold McGee wrote: “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 around 135 F, and it stops when the rising heat denatures it, at around 170 F.” So the longer a sweet potato spends in that zone between 135 and 170 degrees, the sweeter it becomes.
The lowest baking temperature for most home ovens is about 170 degrees, so a sweet potato started at room temperature in a cold oven spends only a short time in the enzyme-activation zone before it reaches 170 and the amylase denatures. This limited enzymatic activity might explain why sweetening roasted sweet potatoes with marshmallows became a popular practice. However, spending one hour between 135 and 170 degrees before roasting provides optimal time for maximum starch-to-sugar conversion. This is easy to do with a sous-vide immersion circulator, but it’s not a common appliance in most American households. The more commonly owned Instant Pot works just as well. If neither appliance is available, you can submerge sweet potatoes in a saucepan of water, heat to 160 degrees, remove from heat, cover, and steep for about 1 hour to maintain the ideal 135-170 range needed to convert starch into maltose.
Using controlled heat to maximize a sweet potato’s inherent sweetness addresses only one aspect of flavor. By glazing the partially cooked sweet potato in a mixture of miso and fat, you create a savory coating that enhances caramelization while introducing rich umami and salinity to balance out the natural sugars.
Miso provides glutamates – the amino acids driving the savory “fifth taste” known as umami. Combined with sweet potato sugars, these glutamates create a single, cohesive flavor rather than distinct tastes. Fat serves as the essential missing link. Although miso is water-soluble, its flavor blooms in fat – whether using melted unsalted butter, heavy cream, tahini, or extra-virgin olive oil. Fat coats the tongue, slowing the release of sugar and salt and turning a potentially jarring contrast into a long, satisfying finish.
Miso-sesame glazed sweet potato rounds
A one-hour warm bath maximizes enzymatic starch conversion into sugar without breaking down pectin too fast. The result is a silky interior that holds its shape for high-heat roasting.
Serves 4.
Ingredients:
2 pounds sweet potatoes, sliced into uniform 1/2-inch rounds
3 tablespoons unsalted butter, melted
2 tablespoons white miso paste (shiro miso)
2 tablespoons pure maple syrup
1 tablespoon unseasoned rice vinegar
1 tablespoon toasted sesame oil
1 tablespoon toasted white or black sesame seeds
Flaky sea salt, such as Maldon
Preparation:
Place the sliced sweet potato rounds into the Instant Pot’s inner pot, adding sufficient water to submerge them completely. Lock the lid, select the sous vide setting, and cook at 150 degrees for one hour. Alternatively, submerge the sweet potato pieces in a saucepan filled with water and bring it to 160 degrees. Remove from the heat, cover the pot, and let it steep for about one hour. This keeps the temperature within the optimal 135-170 F window needed to convert starch into maltose.
While the potatoes are in the water bath, combine melted butter, white miso paste, rice vinegar, and toasted sesame oil in a medium bowl. Whisk until smooth.
Preheat the oven to 425 and line a large-rimmed baking sheet with parchment paper. Gently remove the sweet potato rounds and pat them thoroughly dry with paper towels. Add the rounds to the glaze and gently toss to coat all sides evenly.
Arrange the rounds on the baking sheet, leaving space between each piece. Pour any leftover glaze from the bowl over the tops. Roast for 20 minutes, flip and continue roasting until the glaze bubbles, darkens and forms a sticky, caramelized crust around the edges.
Transfer the hot sweet potato rounds to a warm platter. Sprinkle with toasted sesame seeds and a pinch of flaky salt.
This article appears in October 1-7, 2026.
