I saw a few people talking/asking about scratters. I have just today ground about 20-30 kg with a home made one, powered by an electric drill. If people are intrested I will post some pics and a few details of how I constructed it.
The true answer to apple stained hands is lemon juice. I have just tried it, and it is like magic. I used a few splashes of bottled juice, rubbed it in, and the black/brown was gone, quick rinse and all was good. No soap needed!
Obviously I stained my hands grinding apples for cider! :D