TANNINS ( reference: Cornell University ) [home] [topic page]
A very complex set of chemicals associated with wine are the "tannins". These are chemicals occuring in all plants and are a member of the "polyphenols"- many phenols. Tannin is associated with "astringency" of a wine.
The word "astringent" means "binding, drawing tight, severe, austere". Tannins tend to make the mouth suck inwards.
Tannins have the property of binding proteins together, even precipitate them, so they affect the proteins in saliva making them stringy, hence the effect on the inside of the mouth. They also have the ability to react with bacterial cell walls, polysaccharides, carbohydrates and enzymes, all present in the mouth.
They are responsible for the colours seen in autumn leaves or flowers and the brown colour of Tasmanian mountain rivers..
Literally, tannins are used in tanneries for the production of leathers. Skin proteins are bound when soaked in tannins make the skin a tough material - leather.
Tannins are associated with phenols which are benzene rings with a hydroxyl group attached.
Tannins have many of these phenol groups as part of their structures which can react.
The molecule above is one of many tannins. Note the high number of "rings" with hydroxyl groups - phenols. In the above diagram, the "old" diagrammatic style of benzene is used with alternate single/double bonds.
The chemical linkages of tannins to proteins are interesting. Water molecules form hydrogen bondings with proteins. The tannins' phenol groups push out these water molecules and hydrogen bond with the proteins in their place. As the tannins have very large numbers of phenols, they bind with many proteins at different places thus locking the proteins together.
Some tannins are closely associated with D-glucose, the sugar.
Tannins tend to allow a wine to stay pleasantly drinkable for longer periods. It is by no means the only quality controlling this however.
Red wines have a higher tannin level than whites because of the use of whole bunches, with stems, during the fermentation.
