Read the back of almost any bottle of red or rosé wine, or hear any expert describing such a bottle, and you're sure to hear or read the word 'tannin' at some point. Tannins have become a key component for describing the body or character of any bottle of wine, with wines containing a high tannin content being described as 'full bodied', and those with few tannins being 'light bodied'. It has become very much part of the vocabulary of wine, and yet few of us actually understand exactly what tannins are, and why they are present so predominantly in red wines, and so little in white wines. To understand tannins fully, one would have to know more than just a little about plant biology and the way in which plant life has evolved. However, there are a few simple facts which we can consider to help us improve our knowledge of these special compounds and be able to speak about them with a little more confidence when describing a wine. The Purpose of Tannins Essentially, tannins are found in a wide range of plants, not just grapevines. They occur naturally in leaves, in bark, and noticeably in young fruit on almost all fruit-bearing plants and trees. The tannins present in these lifeforms are responsible for forming complex binding components with the proteins in plants, and in other organic polymers (such as polysaccharides). Most scientists today believe that tannins originally evolved as a sort of defence mechanism for the plant – tannins have a distinctive and bitter taste, and create a powerful astringent effect in the mouth. Think of eating an under-ripe grape or plum, and you can see the effect the tannins have on the tongue and roof of the mouth. This effect could put off herbivores and other animals seeking to eat the plant, and as such they are now present in a wide range of vegetation. When it comes to the grapevines which eventually produce the wines we know and love, the plant itself utilises its strongest tannins rather cleverly. Basically, the vine wants the grapes to be eaten. This is how it spreads its seeds – through the excrement of birds and other animals which eat its juicy fruits. However, when the grapes are young, the seeds within them are not yet ready, and as such, the grapes are extremely astringent and unpleasant to taste. Fascinatingly, it is at the moment when the grapes begin to change colour when the tannin levels drop significantly; the grapes become both more visible (red, blue, black, purple etc) to birds and more delicious to eat at the same time, making the plant more likely to spread its seeds and thrive elsewhere. Tannins and Wine Production When it comes to wine production, the winery wants to have a certain amount of control over how much tannin they have in their wines. The tannins found in wines do not come from the under-ripe fruit of the vine, though, they come from the seeds, the skins and sometimes the stems of the grape. As such, it is the length of time the grape juice has in contact with the skins, seeds and stems of the fruit that dictates just how much tannin there will be in the wine. But why would a winery wish to have tannins in their wine? Why would they insist on keeping these bitter and astringent compounds? Quite simply, wine without tannin, and especially red wine without any tannin, is often flat, uninteresting, and lacking in any character. The 'body' of the wine is what holds the wines complexity, and allows the vintner to balance the different aspects of the wine against each other. Just as if the wine's alcohol content was too low, or flavour or acidity too weak, the wine would be imbalanced and uninteresting, the same applies when it comes to the body, or tannin content of the wine. Tannins and Ageing Tannins are incredibly important when it comes to ageing wines. Young wines often have a stronger tannin presence in the bottle, and this sometimes means that the other, subtler and more complex characteristics of the wine are overshadowed by its astringency. By ageing red wines, either in oak barrels, or in the bottle at home or in a cellar, tannins begin to soften and 'round out', producing more balanced wines capable of expressing more interesting and subtle features. Generally, aged wines are considered far finer than young wines, as there will be a far wider bouquet of aromas and flavours detectable in the bottle, and the wine will be more balanced and interesting on the tongue.
