Sweet potatoes have more natural sugar and moisture than white potatoes, which is exactly why they tend to go soggy rather than crisp in an air fryer if you skip one small step — the extra sugar caramelises and can burn before the inside is properly cooked if you're not careful with temperature too.
The Cornflour Trick
After cutting the fries and patting them dry, toss them in a teaspoon of cornflour before the oil. It absorbs surface moisture and gives the outside something to crisp against — in our side-by-side test against plain oil-only fries, the cornflour batch was noticeably crispier and held that crispness longer after coming out of the basket.
Cutting for Even Cooking
Cut fries a consistent thickness, ideally around 1cm — thinner than that and they can burn before crisping properly given the higher sugar content; much thicker and the inside stays undercooked while the outside is done. Uniformity matters more here than with white potato chips, because sweet potato's sugar content makes the margin between 'crisp' and 'burnt' narrower.
Timing
Cook at 200°C for 15–18 minutes, shaking the basket every 5 minutes. Don't overcrowd the basket — sweet potato fries need space to crisp rather than steam, and because of their higher moisture content, overcrowding affects them more noticeably than it does white potato chips.
Common Mistakes
Cooking at too high a temperature is the most common mistake, driven by treating sweet potato fries the same as regular chips — the higher sugar content means 200°C is close to the ceiling before burning becomes a real risk, whereas white potatoes can handle a slightly hotter cook without the same problem.