Just curious why you want a wash from apple juice? Do you have access to a lot of apple juice cheap or are you wanting the flavor?

I see.... If I was going to attempt it I would actually just do a specific gravity test on the juice.... If it was adequate for possible conversion percentage I would put in a bit of tomato paste for nutrient and pitch the yeast and get after it. I see no reason other than possible ph level being low that it would not work on the same principle as a sugar wash only lower alcohol conversion due to less sugar content. If you can test ph then you can also adjust that with sodium bicarbonate to raise your ph.