 Tannin

Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.The term "tannin" (from Anglo-Norman "tanner", from Medieval Latin "tannāre", from "tannum", oak bark) refers to the use of oak and other bark in tanning animal hides into leather.