Tannins are Astringent

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]. Tannins are found as shapeless yellowish or light brown masses like powder, flakes or sponge. Interestingly, tannins are found almost in all plants and in all climates all over the world. The name ‘tannin’ is derived from the French word ‘tanin’ (tanning substance) and is used for a range of natural polyphenols. Lower plants such as algae, fungi and mosses do not contain much tannin. The percentage of tannins present in the plants, however, varies. While they are present in significant proportions in some plants, many others have too little of them. Tannins are usually found in large quantities in the bark of trees where they act as a barrier for micro-organisms and protect the tree. Apart from tanning, tannins are also used in dyeing, photography, refining beer and wine as well as an astringent in medicines. Significantly, tannins form a vital element of tea [3].