Bitters

An aromatic liquid distilled from herbs, roots and barks of various plants. Bitters was used for "medicinal" purposes as well as an additive to various beverages. The most common brand in the U.S. is Angostura bitters. Bitters do have a high alcohol content. Due to their potency bitters are typically used in very small quantities.

Purchase in any liquor store, or any store that sells alcoholic beverages.