Tannins are astringent, bitter plant polyphenols
that either bind and precipitate or shrink proteins.
The astringency from the tannins is that which
causes the dry and puckery feeling in the mouth
following the consumption of red wine, strong
tea, or an unripened fruit[1]. The term tannin
refers to the use of tannins in tanning animal
hides into leather; however, the term is widely
applied to any large polyphenolic compound
containing sufficient hydroxyls and other suitable
groups (such as carboxyls) to form strong
complexes with proteins and other
macromolecules. Tannins have molecular weights
ranging from 500 to over 3000[2].