tannic acid

tannin

 or tannic acid

Any of a group of pale yellow to light brown amorphous substances widely distributed in plants and used chiefly in tanning leather, dyeing fabric, and making ink. Their solutions are acid and have an astringent taste. They are isolated from oak bark, sumac, myrobalan (an Asian tree), and galls. Tannins give tea astringency, colour, and some flavour. Tannins are used industrially to clarify wine and beer, reduce viscosity of oil-well drilling mud, and prevent scale in boiler water; they have also had medical uses.

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tannic acid [′tan·ik ′as·əd]

(organic chemistry)

C₁₄H₁₀O₉A yellowish powder with an astringent taste; soluble in water and alcohol, insoluble in acetone and ether; derived from nutgalls; decomposes at 210°C; used as an alcohol denaturant and a chemical intermediate, and in tanning and textiles. Also known as digallic acid; gallotannic acid; gallotannin; tannin.

C₇₆H₅₂O₄₆Yellowish-white to light-brown amorphous powder or flakes; decomposes at 210-215°C; very soluble in alcohol and acetone; used as a mordant in dyeing, in photography, as a reagent, and in clarifying wine or beer. Also known as pentadigalloylglucose.