Learning how to clean rusty grill grates with a non-toxic substance is important since you will be cooking on them. Vinegar and salt are both edible substances, but will also remove rust. Mix two cups vinegar and one-cup salt in a bowl. Place your rusty grates in a large heavy-duty garbage sack. Pour the vinegar and salt into the bag and tie it shut. Lay the bag flat on the ground and let the grill soak over night. After soaking, wipe the rust off with an old rag. The salt should act as a mild abrasive to scrape off the rust.