Everyone who owns a gas stove, pin this!! It works! Mine were absolutely disgusting and I tried everything to clean them. It was so gross how much came off! Definitely the best stove grate cleaner ever.
slip grate into gallon size ziploc bag. Do not put any holes in bag. Pour 2-3 T. ammonia into bag. Seal bag & let sit for 12 hrs. Do this overnight. Take grate out of bag in kitchen sink. Rinse the grate thoroughly and scrubb with a nylon scrubber.