A bitter is a beverage flavored with herb and/or root essences that give it a pronounced bitter flavor. Originally these were sold as medicines and cure-alls, but are now used mostly as digestifs.
They are typically thought of in two categories:The cocktail bitters which are added in drops or dashes to flavor cocktails, and the drinking or digestif bitters which are drunk neat or on the rocks.
The common ingredients used in these alcoholic beverages are: Cassia, Gentian root, Orange peel, Quinine from the cinchona bark, and also wormwood leaves. These additives give the bitter taste that is cherished by drinkers around the world.