A bittering agent is a flavoring agent added to a food or beverage to impart a bitter taste, possibly in addition to other effects. While many substances are bitter to a greater or lesser degree, a few substances are used specifically for their bitterness, especially to balance other flavors, such as sweetness. Notable beverage examples include caffeine, found naturally in tea and coffee and added to many soft drinks, hops in beer, and quinine in tonic water.