Tannins are polyphenols found principally in the bark, leaves and immature fruit of a wide range of plants. They form complexes with proteins and other plant polymers such as polysaccharides. It is thought that the role of tannins in nature is one of plant defence: they have an astringent, aversive taste that is off-putting to wannabe herbivores. As an animal or insect begins to munch on plant tissue, the tannins are released from cellular compartments and bind with the proteins and other cell components, making them taste unpleasant and rather indigestible.
==Special Precautions of Tannins==
* Don't confuse with tannic acid : The main cause of confusion concerning tannins is that they're often mistakenly believed to be associated with tannic acid which is used for tanning leather, when this is not the case. Tannic acid is often extracted from oak leaves and has a completely different chemical makeup than polyphenols, so despite the fact that you may have heard that tea tannins (polyphenols) can be used for tanning leather, this simply is not true.