Wine Education - The structure of a wine

On The Grapevine, July 2010
From Mike of Devotion, Wine Correspondant
The components that provide balance and harmony to a wine
In tasting wine it is important to pay attention to the structure of a wine, not just the primary fruit flavours. Balance in wine refers to the interaction and harmony between two or more of the wine's components. An appreciation of the balance of tannins, acidity, alcohol, flavour and other components did much to help in my understanding and enjoyment of wine. I hope this brief guide to the components that make up a wine will also help you to understand and enjoy them more.
The tannins in a wine are derived from the pips, skins and stalks. Tannins can also be picked up by ageing in oak barrels (see below). They are vitally important if a wine is intended to age, as they are a natural preservative. The tannins do not provide flavour but give structure and backbone to the wine. They can be sensed by a furring of the mouth, or puckering of the gums, a sensation very similar to what happens on drinking stewed tea. This is unsurprising, as this effect is also due to tannins, released from the tea leaves after stewing in the hot water for too long.
Tannins are of more importance in the ageing of red wines rather than white. The tannins act as a preservative, and as they fade over many years, the simple, primary fruit flavours have time to develop into the more complex flavours that are found in fine, aged wines. A level of tannins that is sufficient to provide structure, but not so obvious as to dominate the palate, is the ideal when a wine is ready for drinking. For this reason tannins are still important in red wines not intended for long ageing, as they give grip or structure to these wines also. Tannins may also have different qualities, and could be described as harsh, soft, stalky, chalky, etc.


All fruit requires acidity, be it an orange, peach or grape. Acidity is what gives fruit its refreshing, flavoursome sensation. Without it fruit would seem overly sweet and cloying, a little like the sensation derived from drinking the sugary fruit syrup in which some canned fruit is presented. Just like fruit, wine also requires acidity. Too little, and it will seem dull, flabby or perhaps cloying, particularly if it is a sweet wine. Too much, and the wine will be sharp, harsh and undrinkable. Acidity can be detected by the sharpness of the wine in the mouth, particularly around the edges of the tongue near the front.
Some acids, such as acetic acid, are known as volatile acids, and in small amounts these can really lift the flavours in the wine. Too much, and the wine begins to resemble furniture polish, acetone (nail-polish remover) or even vinegar. Higher acidity denotes a wine from a cooler region, such as New Zealand. Lower acid wines come from countries with warmer weather, such as Australia, where acidity in the harvested grapes is often low enough to warrant some chemical acidification.

Alcohol is the product of fermentation of the natural grape sugars by yeasts, and without it wine simply doesn't exist. The amount of sugar in the grapes determines what the final alcohol level will be. In colder climates, such as northern Europe, where the vines struggle to ripen their grapes, sugar levels will be minimal, and consequently such wines often only reach 7 or 8% strength. In very warm climates, however, the final alcohol level will be determined not so much by the amount of sugar but rather by the yeasts themselves. Once the alcohol level reaches about 14 to 15% the yeasts can no longer function and rapidly die off. For this reason, wines with a strength of more than 16% are usually fortified.

The conversion of sugar to alcohol is such a vital step in the process of making wine, that the control of fermentation is the focus of much attention of the modern winemaker. Fermentation generates heat, and a cool, controlled fermentation will result in very different flavours in the wine (in particular, it protects fresh, delicate fruit flavours) when compared with wines where fermentation is allowed to run riot. Although fermentation will start naturally, thanks to yeasts naturally present on the grapes in the vineyard, many winemakers prefer to remove the element of chance by kick-starting fermentation using cultured strains of yeast.


Following on from the above, it is clear that if fermentation is arrested, either as a result of the yeasts failing in a gradually increasing alcohol level in the ferment, or as a result of the winemakers’ intervention, there will as a consequence be some remaining sugar in the wine. Even when the yeasts work is unhindered, most wines still have some small quantities of residual sugar as some sugar compounds are resistant to the action of the yeasts. Clearly, the level of sugar in the wine determines how sweet it tastes. This is quite subjective, however, and even wines that taste very dry have some degree of residual sugar. They remain dry due to the presence of acidity and tannin alongside the sugar. The greater the amount of residual sugar, the sweeter the wine.  Wines can range from very dry ( many  Rieslings) to the great dessert wines of the world (Sauternes, Tokay) which have incredibly high concentrations of sugar.


Many wines are matured in oak barrels, and some are even fermented in oak. Oak from different sources (most comes from either the forests of France or USA) will impart different characteristics on the wine, but in general oak maturation gives aromas of butter, toffee, caramel, vanilla, spice and butterscotch.
French oak may give more buttery aromas, whereas American oak generally gives stronger vanilla and spice aromas. However, the process is relatively more complex as it all depends on how much oak is used, how much of it is new as opposed to re-used, how long the wine stays in contact with the wood, whether the wine is merely aged in oak or whether the fermentation takes place in it, how the oak has been treated, and so on. For instance, barrels that have been 'toasted', which means the cooper has formed them around a small fire, often burning the oak shavings he has produced in the manufacturing process, will have aromas of smoke and toast. Barrels that have been steamed during manufacture, however, may give more oatmeal aromas.


In many wines the yeasts themselves are the cause of certain flavours. When a wine has completed fermentation it remains cloudy and contaminated with dead yeast cells. Many different techniques are employed to clarify the wine, including racking the wine (gently pouring the clear wine off once the dead yeast cells have settled to the bottom) from its lees (the collection of dead yeasts).

Wines that remain on the lees for a long time, however, will take on extra richness and texture, with bready, biscuity aromas and flavours. This technique is employed to add an extra dimension to many Champagnes.


After this assessment of all the components present in a wine, it is still necessary to examine the many flavours that are present in wines, however this will require a further article at a later date.