there are plenty of yeast strains that'll hit 20% plus.
but in this case, it isn't fortified, it is freeze distilled - the water is removed from it because it preferentially solidifies before the alcohol does. Unlike a traditional still, however, this will leave the "gubbins" behind, so you'll end up with beer flavoured alcohol rather than just ... alcohol.
( the mighty badger Aphrodite, on a bar stool, by your side, Thu 4 Aug 2011, 13:47, Reply)