An ester is chemical flavor compound that is created during the fermentation process. Ester formation is primarily dependent on the yeast strain.

In some cases, excess esters are considered an off flavor, and in other instances, it is desired—like in the case of a Bavarian hefeweizen where banana and clove tasting esters are expected. Esters are typically described as fruity, flowery, or spicy scents and flavors in a beer.