My apple wine (done in 60 gal barrels) is consistantly very good in
taste/flavor at 15%. A book I have indicates that using fermentation
with sugar & yeast, 22% is the max that can be achieved. Must agree
with the rest here, though, unless you drink for effect, higher
alcohol contents are conducive to getting drunk on one bottle as
opposed to enjoying your wine if its tamer (11-12%) In my early days I
always made stronger wine only to have my friends tell me how good it
was, drink alot in too little time, then fall down an hour later. Not
a desireable result, so I started leaving out some of the sugar to
tame it down to 12% and the flavor is better & the end result more
tolerable. Champagne yeast is what I used to use to achieve the higher
% as it is more tolerant of higher alcohol content. Good luck.