Did you know that the Eisbock is the strongest of the bock beers?

An extra-strong dopplebock beer in which potency has been heightened by a process of freezing. Since water freezes before alcohol, the removal of ice (eis) concentrates the beer. Produced by lagering beer in very cold cellars at the freezing point of water, and removing some of the iced water, thereby increasing the alcoholic strength of the beer.

So basically, a doppelbock is brewed, then it is frozen and some of the ice is removed, then it is thawed, and alakazam, you have a nuclear powered beer!