Interactions between saliva and wine
From the table above we see that wine only contains about 0.1% tannins (also known as polyphenols). The sources of tannins found in red wine are the seeds, skin and stem of the grapes. When we drink red wine, the tannins react with proteins in our saliva to form water insoluble protein-tannin complexes. A precipitate is formed and as a result, the lubricating properties of the saliva are lost and our tongue feels rough and dry. In other words, we experience the astringency of the red wine.

An elegant experiment to show this is as follows (I learnt this at the 2004 International workshop of molecular gastronomy in Erice):

• Take a sip of a dry red wine, preferably rich in tannin.
• Keep the wine in your mouth for 10-20 seconds without swallowing.
• Spit it into a empty glass and watch how a precipitate forms (this might take a minute or two). Notice how the color changes from red to light red or even pink (see picture below).
• Rinse your mouth by chewing a piece of bread and drink some water.
• Take a small sip of the wine that you just spit out (if you dare!). Since the tannins of this wine have already reacted with your saliva, it is as if they were removed from the wine, leaving a fad and flat wine without much taste at all.

Top: red wine. Bottom: formation of precipitate in red wine mixed with saliva.

The saliva flow rate and the concentration of proteins varies from person to person (the latter with a factor of 20). Furthermore the flow rate and protein concentration also varies throughout the day and is also influenced by what you are eating/drinking and even by the smell of food. As a consequence, a person with a high saliva flow rate and/or a high concentration of proteins is more likely to approve of a red wine rich in tannins than someone with a low saliva flow and a lower protein concentration. Knowing this, you should not be surprised that wine preferences can be very individual.

Found Here: http://khymos.org/wine.php