Rust on the grill grate means it's time to give that grate a thorough scrubbing. After frequent use, food splatters, high heat and exposure to the elements outdoors, cast iron begins to rust. Little bits of rust may transfer onto grilled foods if the grill grate is not properly maintained. Cleaning the rust away from a cast-iron grate requires a gentle soap instead of harsh chemical-based cleaners. If your grill has a porcelain-coated grate that has chipped and rusted due to missing enamel, the grate should be replaced.
Set a few sheets of newspaper on the ground outdoors. Remove the grill grates and set them atop the paper.
Scrape away as much of the rust and grilled-on gunk as possible using a grill-scraping tool or paint scraper and a wire brush. Flip each grate over and scrape the reverse side as well. Use the brush along the sides of each grating as well.
Squirt a little dish soap into a bucket of water. Dip a scrub brush into the water and clean the grill grates with the brush.
Dump the water from the bucket, rinse it out and fill with 1 part vinegar to 4 parts water. Wipe the grates down with a sponge dipped into the bucket, wiping both sides of each grate. Prop the grates up against a table or wall to air dry.
Place the grates back on the grill and heat up the grill until the grill is hot.
Ball up a paper towel and pour enough cooking oil on it to saturate it. Grasp the paper ball with the tongs and wipe down the hot grilling surface with it. Use additional oily paper towels as needed to wipe down all of the grates. This oiling and heating process loosens additional gunk and prepares the grill for use.