In short, it was gross.
I had seen the Pinterest method of soaking the grates in ziploc bags with ammonia. It seemed too simple, but after my success with ammonia and kool-aid, I had a lot of ammonia and nothing to lose. Again.
I carefully slid the grates into giant freezer-sized ziploc bags along with the gas cover. I then measured out 1/4 cup of ammonia, poured it into the bag, and sealed the bag. I laid the bags on cookie sheets for easy transfer. The hardest part of this was measuring out the ammonia without passing out from the noxious fumes. I cannot stress the importance of air circulation enough. The recommendation was to keep the grates cooking in their fumes for twelve hours. In the meantime, I washed my stovetop with this tried-and-true method.
After nine hours, I was anxious and there was a threat of inspection the following day. I wasn't going to risk a grate-less stove. At this point though, the ammonia seemed to be working. What went clear into the bag was now orange. Gross.
I emptied the ammonia and filled the sink with warm soapy water. Some areas of the grates needed a bit of light scrubbing, but nothing taxing. They were quickly washed, rinsed, dried, and back on the stovetop.
Glistening, gleaming, and cleaner than they'd been in two years.
To save you a scroll, here's a side-by-side comparison:
Do you believe in magic now?