A cast iron skillet costs less than a mid-range nonstick pan and will still be working in fifty years. It also attracts more folklore than any other object in the kitchen. Most of that folklore is unnecessary, and some of it is simply wrong.
What seasoning actually is
Seasoning is not oil sitting on the surface. It is polymerised fat: thin layers of oil heated past their smoke point until they chemically bond to the iron and to each other, forming a hard, dark, slick coating. That is why it survives washing and why it builds up over time.
Understanding this settles most of the arguments. Soap does not dissolve a polymer, so washing up liquid is fine. Water alone does not strip it either. What does damage it: long soaking, harsh scouring down to bare metal, prolonged contact with acid, and the dishwasher.
Building it
- Strip if you need to. A new unseasoned or rusty pan gets scrubbed back to clean grey metal. A factory-seasoned pan does not need this.
- Oil, then wipe it all off. This is the step people get wrong. Apply a neutral oil with a high smoke point, then wipe with a clean cloth as though you have made a mistake and want it gone. The pan should look dry, not glossy.
- Upside down in the oven, 220°C, an hour. Upside down so nothing pools. A tray underneath to catch drips.
- Repeat two or three times for a new pan. Then stop and start cooking, because cooking is what actually builds a good surface.
Thick oil is the classic beginner error. It bakes into a sticky, patchy layer that flakes off in sheets. Thin, repeated, boring layers win.
What these pans are genuinely good at
- Anything that needs a hard sear. Their mass holds heat, so food that hits the surface does not cool the pan down and start steaming.
- Going from hob to oven. No plastic, no limits.
- Cornbread, frittata, tarte tatin, roast chicken for two. A skillet doubles as a baking dish.
- Carbon steel specifically for eggs, fish and crêpes, once seasoned. It is lighter and heats more responsively than cast iron, which is why professional kitchens use it.
What they are bad at
Even heating. Cast iron holds heat well but conducts it slowly and unevenly. Preheat it for several minutes over a medium flame, moving it around if your burner is small, rather than blasting it for ninety seconds.
Long, acidic cooking. A tomato sauce simmered for an hour in a lightly seasoned pan will strip the seasoning and taste metallic. Twenty minutes in a well-established pan is fine. Enamelled cast iron has no such limitation, because the enamel is glass.
Being lightweight. A 28cm cast iron skillet full of food is heavy. If your wrists object, carbon steel is the lighter alternative with nearly the same benefits.
The one-minute routine
- While the pan is still warm, rinse under hot water and scrub with a brush or a chainmail scrubber. Washing up liquid if you want it.
- Stubborn residue: coarse salt and a folded paper towel, or simmer a little water in the pan for a minute to loosen it.
- Dry on the hob, not on the rack. Thirty seconds over heat until every trace of water has gone.
- A few drops of oil, wiped almost entirely off with a paper towel. Off the heat. Done.
That last wipe is what prevents rust. Iron plus water plus air is rust, always, and a pan put away damp will show orange by morning.
Rust is not the end
Scrub the orange off with steel wool or a scourer, wash, dry thoroughly on the heat, then re-season two or three times. A pan found rusted in a garage comes back as good as new, which is more than can be said for any nonstick pan ever made.
Myths worth dropping
- "Never use soap." Based on the days when soap contained lye. Modern washing up liquid does not strip polymerised seasoning.
- "Never cook anything acidic." Only true for long cooks in a young pan.
- "You must use flaxseed oil." It produces a hard seasoning that also tends to flake. Any neutral oil works, and the one already in your cupboard works fine.
- "The pan must be black and mirror smooth." A pan that is a bit patchy and cooks well is a good pan. The photograph is not the point.