Why It Works
- Cutting the sweet potatoes into 1/4-inch sticks keeps the outside crispy and the interior tender when cooking.
- Making a slurry for the fries from cornstarch, white rice flour, sugar, salt, and neutral oil helps with browning, crisping, and caramelization.
- Shaking the fry basket and spraying with oil every five minutes further ensures crisp, well-browned fries.
Search for « sweet potato fries » on the r/unpopularopinion subreddit and you will be presented with a long list of posts going back years in which people proclaim their total admiration or utter disgust for the food. If there’s one takeaway from this, it’s that these are clearly not unpopular opinions—sweet potato fries are the definition of divisive. While some of the haters out there will never accept a sweet potato in place of the classic, many more object to a real problem that plagues many a sweet potato fry, which is that they’re too often not as crispy as a fry should be. When you bite into something expecting it to mirror a French fry, but you’re left with a floppy, mushy, and soggy stick, there’s not much that will keep you coming back for more.
But what if you could make a sweet potato fry that’s truly crispy on the outside and fluffy within? Even better, what if you could do it in an air fryer without the mess and inconvenience of a spattering pot of oil? After many rounds of testing, our test kitchen colleague Marianne Williams discovered the secret to air-fryer sweet potato fries at home by creating the ideal coating to turn the sweet potatoes into crispy sticks with a perfect bite. Below, we explain her steps for success.
The Secret to Crispy Sweet Potato Fry Success
In an effort to crack the code on crispy air-fried sweet potato fries, Marianne knew the secret might lay in a coating of a starch like cornstarch along with a light amount of oil, after all, sweet potatoes have significantly less starch than a russet potato and even in an air fryer, you need to some oil for even browning and crisping.
To test it out, she started with batches that were coated in a dusting of dry starches like cornstarch, rice flour, and potato flour, along with some oil. For a control, she tested those against a batch that was seasoned simply with salt and pepper and a light coating of oil. The starch coatings worked, though the potato starch batch burned and none created anything close to a lasting crispness.
Serious Eats / Marianne Williams
Her next round of tests added sugar along with a combination of rice flour and cornstarch—the two successful starches from the first round of tests. This worked even better—the fries were truly crisp—but the coating was uneven. Marianne first tried to solve that problem with cooking spray instead of oil, but her breakthrough came when she took the extra step of stirring the coating ingredients together first to form a slurry before applying them to fries. That, combined with being thoughtful about the thickness of the fries and the method of cooking them, are the keys to success.
For the Crispiest Air-Fryer Sweet Potato Fries, Make a Slurry
Serious Eats / Morgan Hunt Glaze
Instead of adding each ingredient separately to the cut sweet potatoes, the solution to the most even, crispiest coating is to make a slurry first from cornstarch, white rice flour, sugar, salt, and neutral oil. The small amount of sugar in the slurry helps achieve the ideal browning of the fries, and aids in both crisping and caramelization. This slurry makes it easier to coat each fry evenly, which yields perfectly crispy results that brown evenly all over.
Cut the Potatoes 1/4 Inch Thick Sticks
The thickness of the potato sticks has a critical impact on how the fries turn out. Too skinny and the fries are all crispness with no fluffy interior. Too thick and you’re at risk of losing the crispness to an expanse of moist interior. The sweet spot we found is 1/4 inch thick, which produces what we consider to be the ideal balance of sweet and tender interior and crispy shell.
You can opt to keep the peel on your sweet potatoes, but just be mindful that they may create a tougher exterior on the fries. If you do keep the skin on, make sure to give them a good scrub before cutting.
Get the Cooking Method Right
We found that for the ideal sweet potato fry, it’s not enough to coat your potatoes with the starch slurry, pop them in the air fryer, and hope for the best. We first had to get the temperature right—we went as high as 390ºF (199ºC), but that temperature proved too high. So we landed on 385°F (196ºC) for about the first 13 minutes, followed by a reduced temp of 375ºF (190ºC) for the rest of the time—this gives enough of an initial blast of heat to crisp the exterior but is gentle enough to prevent scorching.
Serious Eats / Morgan Hunt Glaze
At the same time, you can’t just let the fries cook from start to finish without tossing them—they’ll never crisp and brown evenly like that. Instead, you need to check on the fries every five to six minutes, shaking the basket and spraying the fries generously with cooking spray each time until they start to brown. Continue this method of shaking the basket and spraying the fries with oil every five minutes until you’re left with crispy, well-browned sweet potato fries.
How to Make Flavor Variations
While this recipe is for basic air fryer sweet potato fries, you can use it as a jumping-off point for a whole range of flavor variations. There are no hard-and-fast rules here, but spices like smoked paprika, mustard powder, black or white pepper, garlic powder, and even dried herbs would work great to switch up the flavor. Given a sweet potato’s natural sweetness, warm spices like cinnamon, nutmeg, and clove could also work.
In all cases, the seasonings can be whisked into the slurry to ensure an even application on the fries. Alternatively, the fries can be tossed in the seasonings after cooking, such as in a light coating of cinnamon sugar or a dusting of a barbecue-flavored dry rub.
Editor’s Note
This recipe was developed by Marianne Williams; the headnote was written by Daniel Gritzer.
