Tannins: classification and definition.

The name ‘tannin’ is derived from the French ‘tanin’ (tanning substance) and is used for a range of natural polyphenols. Since ancient times it is known that certain organic substances have tanning properties and are able to tan animal skins to form leather. Prehistoric tribes already knew about the tanning of protective animal hides with brain material and the fat of the killed animals. However, precisely what happens to the skin during the tanning process was only elucidated during the twentieth century with the help of modern analytical techniques. Real tanning is understood as the crosslinking of the skin’s collagen chains, while false tanning entails the filling of hollow spaces between the skin’s collagen chains. The traditional tanning of animal skins by means of plant tannins has been replaced gradually by mineral tanning, as represented by alum tanning (or glacé tanning, a variant of alum tanning) and more recently, since the end of the nineteenth century, by chromium tanning. In nature the tannins are found worldwide in many different families of the higher plants such as in chestnut and oak wood, Divi-Divi, Sumach, Myrobalaen, Trillo, Valonea or plant galls; depending on their origin, their chemistry varies widely, having a molar mass of up to 20000 D. High tannin concentrations are found in nearly every part