When its distilled it becomes a liquor. I didn't see anything about the brewing process but my understanding is that you can't get something much stronger than wine through fermentation alone. I'm betting this is a beer that has been fortified with extra alcohol, possibly blended with whiskey which is after all just distilled beer.
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Dogfish Head has yeasts that will get to about 25% alcohol (almost twice as strong as wine), so the old limits aren't necessarily true. That being said, I don't have a clue how they get to 55% alcohol.
Don't the yeast just suffocate themselves in alcohol after awhile? I wonder if you can filter out the alcohol and keep on adding sugars to the mix to keep the yeast metabolizing without dying off and then add back the alcohol in a final mix.