How to restore grill grates: cast iron, stainless, and porcelain.

Cast iron grates are the most restorable grate material on a grill. The iron itself is very thick and extremely resistant to structural failure. Almost every cast iron grate problem you will encounter on a hand-me-down is a surface problem, not a metal problem.

1. Soak in 1:1 white vinegar and water for about an hour. The acid loosens rust without aggressive scrubbing. Keep it to roughly an hour: vinegar is acidic and will keep eating the metal if you leave it overnight.
2. Scrub to bare, gray metal. A pumice grill stone or a bristle-free brush works well. Aim for clean cast iron with no orange-brown remaining. Rinse well after.
3. Dry completely, immediately. Cast iron flash-rusts in minutes when wet. Towel dry right after rinsing, then heat the grate on the grill at low or in a 200F oven for 10 to 15 minutes until bone dry.
4. Re-season with a thin oil coat. Wipe a very thin layer of high-smoke-point oil (canola, grapeseed, or flaxseed) over every surface of the dry grate. Run the grill at about 400F for an hour. Let it cool and repeat once or twice more. Thin coats cure smooth; thick coats turn sticky.

For a more detailed cast iron method with tips on stubborn rust and long-term maintenance, see how to restore cast iron grill grates.

Stainless steel grates do not rust the way cast iron does. The light surface discoloration and minor corrosion spots you will see on old stainless are superficial.

1. Preheat and burn off residue. Run the grill hot with the lid closed for 10 to 15 minutes. The heat turns baked-on carbon to ash, which makes it much easier to brush off than trying to clean it cold.
2. Scrub while warm. A bristle-free brush or stainless scrubber clears the ash and light rust. For more stubborn spots, a paste of baking soda and water applied with a cloth and rubbed in the direction of the metal grain lifts surface corrosion without scratching.
3. Rinse and dry. Rinse with water, wipe dry. Stainless does not require seasoning oil the way cast iron does. Keeping it dry is the maintenance.

When to replace stainless: If the grates are warped badly enough to rock or tip, they will not cook evenly and will not flatten back down. That is the replacement signal, not surface corrosion.

Porcelain-coated grates have a glassy surface fired over a steel or cast iron core. When the glaze is intact, they are easy to clean and resist sticking. When the glaze chips, bare metal is exposed, rust follows fast, and the porcelain flakes can end up in food.

If the glaze is intact: Clean with a soft nylon brush or silicone brush on a warm grate. Do not use wire bristles, abrasive pads, pumice stones, or metal scrapers on intact porcelain. A soak in warm soapy water loosens baked-on residue gently. Rinse and dry.

If the glaze has small chips: Watch them. Small chips that have not yet begun to rust may stay stable for a while. Do not scrub the chipped area or the surrounding glaze aggressively.

If the glaze is chipping with rust spreading underneath: Replace the grates. Once rust is running under the glaze, the coating continues to lift and the rust spreads. Restoration cannot stop that process from here.