Eisbocks are created by freezing off a portion of the water, and removing it from the beer. This form of concentration, of sorts, increases the beer's body, flavor, and alcohol content. They can range from near black to as light as tawny red. Hop bitterness and flavor are mostly cast aside with a big alcohol presence replacing it, which can range from sweet to spicy, and fruity to often times fusel. Look for a heavy or almost syrupy body with tons of malty flavor.
Average alcohol by volume (abv) range: 9.0-15.0% -- BeerAdvocate