How to clean cast iron, and get rust off it

Step by step

1. 1

   Wash while warm

   Once the pan is warm but not hot, wash it with warm water and a stiff brush, nylon scrubber or pan scraper. A small amount of dish soap is fine according to one cast iron maker and the Maine and Illinois extension services.

   Why: Food lifts off a warm pan easily, and well-bonded seasoning survives a gentle wash. Mississippi State Extension prefers no soap; sources differ, but all agree to skip harsh detergents and large amounts.

2. 2

   Scrub stuck food with salt

   For stuck-on bits, scrub with a paste of coarse kosher salt and a little water, or scrape with a pan scraper, instead of soaking.

   Why: Salt is abrasive enough to lift food but gentler on seasoning than steel wool, and it avoids the long water contact that causes rust.

3. 3

   Dry it completely, right away

   Towel-dry immediately, then set the pan on low heat for a few minutes to drive off any remaining moisture.

   Why: Bare iron rusts quickly anywhere water is left, including on the underside and handle.

4. 4

   Oil it thinly

   While the pan is still warm, rub a very thin layer of cooking oil over the inside with a paper towel, then wipe off any excess so it looks almost dry.

   Why: The oil maintains the seasoning and blocks moisture. Thick oil turns sticky and gummy.

5. 5

   Store it dry

   Keep it somewhere dry. If you stack pans, put a paper towel inside to absorb humidity.

   Why: Damp storage is one of the main causes of rust on cast iron.

What seasoning is, and what it rules out

Cast iron is hard, heavy and somewhat brittle iron that rusts readily in the presence of moisture. What protects it is seasoning: thin layers of oil heated until they polymerize into a hard, slick, water-resistant coating. Everything about cleaning cast iron follows from protecting that coating.

That rules out soaking and the dishwasher, which strip seasoning and cause rust; air-drying and damp storage; steel wool for routine cleaning, which one manufacturer reserves for rust removal; and long contact with acids. Acidic foods such as tomatoes also wear seasoning down, and Illinois Extension notes cast iron leaches more iron into acidic, moist foods. Enameled cast iron is different: it has a glass enamel coating instead of seasoning, so follow its maker's directions.

How often: clean after every use. Re-season when the surface looks dull, dry or patchy, when food starts to stick, or after removing rust.

How to get rust off cast iron and re-season it

Rust on cast iron is usually only on the surface, and rusty pans, even old ones, can usually be restored rather than thrown out.

1. Scour off the rust with steel wool in warm soapy water until you're back to bare gray or black iron. Rinse.
2. Dry completely, on low heat if needed.
3. Oil thinly inside and out, including the handle and underside, and wipe off the excess.
4. Bake it: put the pan upside down on the center or top rack of an oven preheated to 450 to 500°F, with foil on a lower rack to catch drips, bake for 1 hour, and let it cool in the oven. That's one cast iron maker's method; Mississippi State Extension seasons at 350°F and repeats 3 to 4 times. Several thin coats build a better surface than one thick one.

Mississippi State Extension also lists two gentler options for light rust: scrubbing with kosher salt and a wet towel, or soaking the rusted area in white vinegar for no more than 15 minutes at a time, then washing and re-seasoning. Acid attacks the iron and seasoning too, so keep vinegar soaks short. More on rust on cast iron.

How stains behave on cast iron, and spot-treating rules

On cast iron, "stains" are really three things: rust (orange, from moisture), burnt-on food (black, crusty, raised), and dull or sticky patches where seasoning has worn away or oil has built up. None of them respond to the stain removers used on fabric or counters: bleach, oxygen bleach, peroxide and solvents aren't cast iron cleaners.

The rules for any mark: scrape or salt-scrub rather than soak; use steel wool only for rust, and re-season afterward; keep acids brief; and always finish by drying and oiling. A sticky patch means too much oil was applied: heat the pan and wipe it, or scrub it back and re-season with thinner coats.

By situation

Cleaning cast iron after cooking

Scrape out food, wash with warm water and a brush while the pan is warm, dry it on the burner for a few minutes, and wipe on a thin film of oil. Don't leave it sitting in the sink overnight.

Cast iron griddles

Same method as a skillet. A pan scraper handles the flat surface well. Make sure the underside and any grooves are dried thoroughly, since large flat pieces are easy to put away damp.

Cast iron grates on a gas stove

Stove grates are often enamel-coated cast iron, so seasoning rules may not apply. One appliance maker says to wash them in hot soapy water, scrub burned-on food with a plastic scouring pad, then rinse and dry, and not to use bleach or rust removers on them. See stovetop and grates.

Cast iron grill grates

Bare cast iron grill grates follow the same principles as a skillet: brush off food while warm, dry completely, and keep a thin coat of oil on them so they don't rust outdoors. Remove rust with steel wool and re-season. Porcelain-coated grill grates are a different finish; follow the grill maker's guidance for those.

Enameled cast iron (Dutch ovens)

The enamel replaces seasoning, so it can be washed with dish soap and doesn't need oiling. Follow its maker's directions.

What not to do

• Don't soak cast iron or put it in the dishwasher. Standing water and dishwasher detergent strip seasoning and cause rust.
• Don't let it air-dry or store it damp. Bare iron rusts quickly in moisture.
• Don't apply thick layers of oil. Excess oil leaves a sticky, gummy surface instead of hard seasoning.
• Don't leave vinegar on rusty iron for long. Acid attacks the iron and seasoning; Mississippi State Extension limits soaks to 15 minutes at a time.
• Don't use chlorine bleach on cast iron. It isn't a cast iron cleaner, and extension guidance lists it as damaging to cast iron.

Other methods that work

Kosher salt scrub

Coarse salt with a little water or oil on a paper towel scours off stuck food and light rust without soaking.

Caution: Rinse, dry and oil afterward.

Short vinegar soak for rust

Mississippi State Extension suggests soaking rusted areas in white vinegar for no more than 15 minutes at a time, then washing and re-seasoning.

Caution: Longer soaks attack the iron. Re-season immediately afterward.

Stain still there?

The surface is sticky after seasoning

Too much oil was applied. Bake it again at seasoning temperature, or scrub the sticky layer off and re-season with much thinner coats, wiping off the excess each time.

Food sticks and the pan looks dull or gray

The seasoning has worn away. Clean it, dry it and re-season in the oven, and avoid long-simmered acidic foods until the coating builds back up.

Safety

• Cast iron holds heat for a long time: use a mitt, and let it cool to warm before washing.
• Cast iron is brittle and can crack if dropped.

Never mix cleaning products; see chemicals you must never combine.

Questions

Stains on cast iron

• Rust on cast iron

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