Which characteristic of beer is directly impacted by hop variety?

The correct answer is aroma. Different hop varieties contribute distinct aromas to beer, which can range from floral and citrusy to earthy or spicy. The different compounds found in hops, such as essential oils, play a crucial role in shaping the aromatic profile of the beer. Brewers select specific hop varieties to achieve desired aromas that complement the overall flavor profile of the beer. This characteristic is often what defines the identity of certain styles, particularly in IPAs where the aromatic quality is highly emphasized.

Other characteristics like color, carbonation, and alcohol content are influenced by different brewing ingredients and processes. Color is primarily determined by the malt used; carbonation is influenced by the fermentation process and amount of sugar; and alcohol content is a result of the fermentation of sugars in the wort. While these elements are important, they do not vary specifically with hop variety in the same way that aroma does.