What defines the altbier brewing style?

The altbier brewing style is defined by hybrid fermentation using ale yeast. This process involves fermenting at slightly cooler temperatures than typical ale fermentations, which allows for the development of cleaner flavors while still incorporating some of the fruity esters associated with ales. Altbier originates from Düsseldorf, Germany, and the term "alt" means "old" in German, referring to the traditional brewing method that predates the widespread adoption of lager yeasts.

This style exemplifies a balance between ale and lager characteristics, allowing brewers to produce a beverage that is refreshing yet complex. The fermentation process captures the benefits of both yeast types, resulting in a beer that has a smooth, crisp profile, reminiscent of a lager, but with some of the aromatic and flavor nuances typical of ales.

The other options, while touching on various aspects of beer brewing, do not accurately capture the essence of the altbier style. For instance, altbiers are not exclusively brewed with lager yeast, nor are they known for being overly hoppy or strongly sweet. Instead, they balance malt sweetness with a moderate hop bitterness, enhancing drinkability and flavor without overwhelming the palate.