If you want to make your stainless steel grates look new again, always clean them after use. Do not let the food debris sit because it will be harder to clean. Scrub it with a stainless steel grill brush or a metal scraper. You can also use vinegar and foil for cleaning.  Vinegar can help soften and melt burnt food on the grill and the foil is very effective in taking off debris without scratching the surface. A pressure hose is also a good way in getting your grates clean. Place the grill grates against the wall and use a high-pressure nozzle to spray off burnt on debris. Dry them with a towel after. Remember to always clean grates regularly and properly every after use to keep them looking new.