Have you ever peered into another person's spittoon at a wine tasting and contemplated their "stringy bits"? In fact, a closer inspection of the "bits" produced by different people will reveal that, like snowflakes, no two are identical. Some look like delicate and ornate maroon coloured curtains, swaying precariously above the wine below. Others float on top of the wine's surface like a cake of purple soap that has been left in the bath water overnight.

..I suspect I might be alone in my interest of this, but, my fascination emanates from knowing that these human "spittle portraits", are the public display of what is a wonderful facet of red wine; astringency.

Astringency is the drying, roughing and sometimes puckering sensation that is experienced after tasting most red wines. All the truly great red wines of the world produce soft supple mouth-coating astringency. The evocative term "slippery" has also been used by some wine-writers to describe the pleasurable feeling of a high quality astringent sensation. Feeling is the operative word here, as although astringency is an in-mouth experience, it is a touch sensation not a taste as one might expect.

So what causes astringency, and what does it have to do with spittoon residues? Red wines are rich in substances called phenolics. These substances are almost exclusively located in the skins and seeds of grapes, and are extracted from them during fermentation. There are hundreds of different types of phenolics in red wine, however, depending on their chemical structure, these substances play quite different roles in the way a wine looks, tastes and feels. One class of phenolics called the anthocyanins give red wine its colour, another called the catechins are bitter. Another type, officially called the polymeric flavan-3-ols, but better known as tannins, are primarily responsible for astringency.

Saliva contains a number of proteins that lubricate the surfaces of the mouth. When we taste a red wine, these salivary proteins interact with the wine's tannins. When a protein mixes with a tannin, they react and join, and react and join, ad infinitum. The proteins are effectively mortared together by the tannins. This results in the formation of "super structures" that are so heavy they precipitate, and are consequently spat out. As the lubricating proteins are in the spittoon rather than in the mouth, then the oral surfaces become dry and fail to slip easily across each other. Touch receptors in your mouth, which normally track the food in your mouth so that you can time your swallowing, then signal to the brain the existence of the roughing and drying sensation of astringency. As an short aside, each person's salivary composition is slightly different, which explains the individual nature of each persons "glyco-protein-flavan-3-ol complexes (aka stringy bits)".

Red wine astringency can be assertive and yet display very subtle nuances. Many words have been used to describe these. They include those that have been evoked by the feeling of having fine particles on the surface of your mouth (Powdery, Chalky, Grainy), those that relate to the roughness of the feeling inside the mouth (Silky, Emery, Velvety, Furry), and others can be related to the fact that the very astringent wines often cause your mouth to move (Pucker, Chewy, Grippy and Adhesive). Other positive terms include Soft, Supple, Fleshy, and Rich, and on the unpleasant downside, there are sensations of coarseness and hardness. Recently, a sensory wheel in the genre' of the wine aroma wheel giving an extensive list of wine mouthfeel terms has been developed. Laminated A3 copies can be obtained from the Australian Society of Viticulture and Oenology (61 08 83036607). Full proceeds go to furthering the aims of the Society.

Now, while you consider the newfound importance of spittoon residues, I'll just help myself to a very drying, yet velvety, 1996 Wynns John Riddoch Cabernet Sauvignon. But this time I can assure you that I'm planning to keep my glycoprotein-flavan-3-ol complexes to myself!