Prep the onions: Peel onions and trim the ends. Slice them into thin, even half-moons or rings, about 1/8 inch (3 mm) thick. For onion flakes, you can also finely chop.

Separate the layers: Gently pull apart the slices so the layers aren’t clumped. This helps them dry evenly and faster.

Optional soak: If you want a milder taste, soak the slices in cold water for 10 minutes, then drain and pat very dry. Removing excess moisture speeds drying.

Preheat the air fryer: Set to 130–140°F (55–60°C) if your model allows low temps. If not, use the lowest setting (often 150–170°F / 65–75°C). The lower the better for drying without browning.

Arrange the onions: Line the basket or tray with a mesh mat or parchment with holes. Spread onions in a single, loose layer. Avoid piling—overcrowding traps moisture.

Dehydrate: Air fry for 60 minutes, then toss and redistribute. Continue drying, checking every 20–30 minutes. Total time is typically 2–4 hours depending on thickness, variety, and your air fryer.

Rotate trays if needed: If using a multi-rack air fryer, rotate trays top to bottom midway through to ensure even drying.

Test for doneness: Onions should be brittle, dry, and snap cleanly. No soft or leathery spots. If they bend, they’re not done.

Cool completely: Let the onions cool in a dry bowl for 20–30 minutes. Residual warmth can create condensation in storage.

Optional powder: For onion powder, grind fully cooled flakes in a spice grinder until fine. Sift for a smooth texture.

Season or blend: Leave plain for versatility, or mix with a pinch of salt, pepper, or herbs for a ready-to-use topping.