Top producers (and I am not talking about the likes of the big supermarket brands of Hardy's, Jacob's etc) don't tend to add much in the way of "additives" anyway, but as for what happens around the vines and in the preparation of the production facitlities is a different matter even for Organic Wines - see
http://www.timesonline.co.uk/article/0,,1145-1 760215,00.html
Beyond Organic are Biodynamic wines which are, I think, a bit more in keeping with what you would imagine from an Organic producer with tighter controls but also a bit of new age moon cycle stuff and so on <g>. On the down side of this though is that such wines tend to be harder to source and more expensive.