cleaning chinchilla shelves

I am wondering the best way to clean the pine shelves in my cage.
I usually just wipe them off while cleaning and once a month I spray them with a 50/50 vinegar water mix then wipe them off.
I soak them in vinegar and water then sand them when I do a big clean or if I think they need it (approx every other month).... but I find both of these methods don't really remove the stains that I want to remove.
Am I not leaving the vinegar on long enough? how do I remove the stains?

Any tips?
Thanks!