Hello Claire. What you are observing is a fundamental biological and culinary process known as osmosis.
Fish muscle tissue contains a high percentage of water—typically around 70 to 80 percent—stored within delicate cells. When you sprinkle salt over the surface of the raw fillet, the salt crystals dissolve into the thin film of moisture on the exterior, creating a concentrated saline solution.
Because the cell walls act as semipermeable membranes, water naturally travels from an area of lower salt concentration (inside the cells) toward the area of higher concentration (the salted surface) in an effort to balance osmotic pressure. This rapidly pulls moisture outward, leaving a noticeable puddle of water on the surface of your fish.
In an air fryer, this excess surface moisture causes the fish to steam rather than crisp, because the heat must work to evaporate all that water before any browning can occur.
To achieve a crispier result, you have two great approaches:
1. Salt immediately before cooking: Season the fillet just seconds before placing it into the preheated air fryer, so the salt does not have enough time to draw out the liquid.
2. Dry brine and pat dry: Salt the fish 20 to 30 minutes in advance, allow the moisture to surface, and then thoroughly pat the fillets dry with paper towels before cooking. This process firms up the protein structure while ensuring a dry surface that browns beautifully.
I hope this breakdown is helpful for your future cooking!
