Tartaric acid is a white crystalline diprotic organic acid. It occurs naturally in many plants, particularly grapes, bananas, and tamarinds, and is one of the main acids found in wine. It is added to other foods to give a sour taste, and is used as an antioxidant. Salts of tartaric acid are known as tartrates. It is a dihydroxy derivative of succinic acid. Tartaric acid was first isolated from potassium tartrate, known to the ancients as tartar, c. 800 by the Persian alchemist Jabir ibn Hayyan, who was also responsible for numerous other basic chemical processes still in use today. The modern process was developed in 1769 by the Swedish chemist Carl Wilhelm Scheele. The chirality of tartaric acid was discovered in 1832 by Jean Baptiste Biot, who observed its ability to rotate polarized light. Louis Pasteur continued this research in 1847 by investigating the shapes of ammonium sodium tartrate crystals, which he found to be asymmetric. Pasteur was the first to produce a pure sample of levotartaric acid.