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.
Prior to the introduction of hops, many other bitter herbs and flowers were used as bittering agents in beer, in a mixture called gruit, which could include dandelion, burdock root, marigold, horehound (the German name for horehound means "mountain hops"), ground ivy, and heather.
Other substances 
Various other substances are used, including:
Other uses 
Other prominent uses of bittering agents include:
- "Understanding Beer - A Broad Overview of Brewing, Tasting and Analyzing Beer - October 12th, 2006, Beer & Brewing, The Brewing Process". Jongriffin.com. Retrieved 2012-05-20.
- For example, Goya Dry by Helios brewery of Okinawa