Tannic acid is a specific commercial form of
tannin, a type of
polyphenol. Its weak
acidity (
pKa around 10) is due to the numerous
phenol groups in the structure. The
chemical formula for commercial tannic acid is often given as C
76H
52O
46, which corresponds with decagalloyl glucose, but in fact it is a mixture of polygalloyl glucoses or polygalloyl quinic acid esters with the number of galloyl moieties per molecule ranging from 2 up to 12 depending on the plant source used to extract the tannic acid. Commercial tannic acid is usually extracted from any of the following plant part: Tara pods (
Caesalpinia spinosa), gallnuts from
Rhus semialata or
Quercus infectoria or Sicilian Sumac leaves (
Rhus coriaria).