Cast iron gas stove grates can be a real problem to clean. I have a sure fire way of cleaning them. But before I get into it here is an embarrassing before picture.
WHAT YOU NEED
An ammonia based cleaner ( we have Handy Andy here)
Black garbage bags
A pressure sprayer ( or regular hose with sprayer attachment)
Put some ammonia cleaner onto the stove grates and place them into the garbage bag, lay the garbage bag outside in the sun for a couple of hours.
Remove from bag and spray clean. Seriously, minimal effort and so clean, it even gets that weird sticky feel them off.
All you need to do now is let them air dry, then put them back, give them a wipe with a damp sponge and that's it. Easy right?