Which of the following is considered a primarily yeast-derived flavor?

Esters are indeed considered primarily yeast-derived flavors. During fermentation, yeast produces various compounds, including esters, which contribute fruity and floral flavors and aromas to beer. These characteristics can include notes like banana, apple, pear, and others, depending on the yeast strain being used and fermentation conditions. This makes esters a defining aspect of many styles of beer, particularly in those that emphasize yeast characteristics, such as Belgian ales and wheat beers.

Hops are responsible for bitterness and aromatic contributions in beer, but they are derived from the hop plant, not yeast. Caramel flavors usually come from the malting process, particularly from specialty malts that have been kilned at higher temperatures, leading to the development of caramel and toasty notes. Bitterness is specifically attributed to the alpha acids present in hops, which are not related to yeast at all. Therefore, esters stand out as the primary yeast-derived flavors, showcasing the yeast's vital role in developing the sensory profile of beer.