In reply to ianj:
If it's a 30m wall rope the twists should be easy enough to work out by pulling the climber's end each time you do a route.
It's possible that if the rope is longer or the routes are short you're not allowing the belayer's end to spin the twists out (it stays on the floor too long) as you pull it through. In which case dragging it halved along a floor/field will probably do the trick.
It's also possible that something you do keep putting the twists back in, your belay device, belaying technique, coiling/storage method or even just clipping both krabs at the top can sometimes introduce twists, don't ask me how, it's witchcraft so far as I can tell!
jk