Tannic acid is a specific form of tannin, a type of polyphenol. Its imperceptible acidity (pKa roughly 6) is due to the numerous phenol groups in the structure. The chemical method in behalf of commercial tannic acid is often foreordained as C76H52O46, which corresponds with decagalloyl glucose, but in in reality it is a ragout of polygalloyl glucoses or polygalloyl quinic acid esters with the horde of galloyl moieties per molecule ranging from 2 up to 12 depending on the spy source euphemistic pre-owned to excerpt the tannic acid. Commercial tannic acid is usually extracted from any of the following weed parts: Tara pods (Caesalpinia spinosa), gallnuts from Rhus semialata or Quercus infectoria or Sicilian sumac leaves (Rhus coriaria).

According to the definitions provided in apparent references such as ecumenical pharmacopoeia, Food Chemicals Codex and FAO-WHO tannic acid monograph only tannins sourced from the above-mentioned plants can be considered as tannic acid. Sometimes extracts from chestnut or oak wood are also described as tannic acid but this is an faulty expend of the term. It is a yellow to light brown amorphous powder.