Tannins are complex organic compounds found in many plants. They have high molecular weights ranging from 500-3000 Da and are soluble in water and dilute alkalis. Tannins can be classified as hydrolysable, condensed, or pseudo tannins. Hydrolysable tannins can be broken down by acids or enzymes into gallic or ellagic acid. Condensed tannins are resistant to hydrolysis and contain catechin units. Tannins have medicinal properties like stopping bleeding and being an antioxidant. They can be identified using tests like reacting with gelatin or ferrous sulfate.