I'm not really a fan of harsh chemicals but my stove top grates have become burnt and gross to the point that scrubbing won't get them clean.
I read that soaking over night in ammonia will help. I got this bottle for 99cents at the Commissary.
I put each grate in a freezer bag and poured maybe a 1/2 cup of ammonia in and sealed the bag.
Then placed them in the sink and let sit overnight.
They just wiped clean! I rinsed under water and just wiped the grime off with a sponge. YAY!