Cast iron: how to season it and stop it rusting
Cast iron has a reputation for being difficult. It is not difficult — it is just different, and most of the folklore around it is wrong.
What seasoning actually is
Seasoning is not oil sitting on the pan. It is polymerised oil: thin layers of fat heated past their smoke point until they chemically bond into a hard, plastic-like surface fused to the iron. That is why a well-seasoned pan is slick and dark rather than greasy.
This matters because it explains everything else. You cannot build seasoning with a thick layer of oil — it will not polymerise, it will just go sticky. And you cannot destroy seasoning with a bit of washing-up liquid, because it is not oil any more.
How to season, properly
- Wash and dry the pan completely. Warm it on the hob for a minute to drive off the last moisture.
- Add half a teaspoon of a high smoke point oil — grapeseed, sunflower, rapeseed or flaxseed. Not olive oil, not butter.
- Rub it over every surface, inside, outside and handle. Then wipe it all off with a clean cloth as if you had made a mistake. The film you cannot see is the right amount.
- Oven at 220–230°C, pan upside down on the top shelf, tray underneath. One hour. Turn the oven off and let it cool inside.
- Repeat two or three times for a new or stripped pan.
Thin layers, repeated. A thick layer gives you a sticky, patchy finish that flakes.
Everyday cleaning
- Clean it while it is still warm. Hot water and a stiff brush handles almost everything.
- Yes, a little washing-up liquid is fine. Modern detergent does not strip polymerised seasoning. What strips it is oven cleaner, a dishwasher cycle or long soaking.
- Stuck-on food: coarse salt as an abrasive, or simmer a centimetre of water for a few minutes and it lifts.
- Dry it immediately on the hob, not on a rack. Then a few drops of oil, wiped almost entirely off, while it is warm.
Rescuing a rusted pan
Rust is cosmetic on cast iron. Almost nothing is beyond saving.
- Scrub the orange off with steel wool or a chainmail scrubber. Be thorough; go back to bare grey metal in the affected areas.
- Wash, dry completely, warm on the hob.
- Season three times as above.
For heavy build-up of old sticky seasoning, a 50/50 white vinegar and water soak for no more than an hour will loosen it — then rinse, dry and re-season immediately, because bare iron rusts within hours.
What not to cook in it, at first
Highly acidic dishes — long tomato sauces, wine reductions — will eat into young seasoning and can take on a metallic taste. Once the pan is properly black and slick after a year of use, a quick tomato dish is fine. Enamelled cast iron has no such limit; that is its advantage.
Storage
Dry, with a paper towel between stacked pans so trapped moisture cannot sit on the surface. Do not store it with the lid on — a sealed pan traps humidity, and humidity is the only real enemy.
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