What is wine?
In very general terms, wine is an alcoholic drink made by fermenting the juice of fruits or berries. The official European Union definition is more specific: 'The product obtained from the total or partial alcoholic fermentation of fresh grapes, whether or not crushed, or of grape must'.
This official definition distinguishes 'proper' wine from wine made from kits, or the once-popular 'British' wine, made from grape juice concentrate.
The main difference between the production of red and white wine is that red wine is made by fermenting the juice in contact with the skins and flesh of the grapes, whereas white wine is made by fermenting just the juice after the skins and flesh have been removed in the press. This is because the colour and tannins which are vital to red wine are found in the skins of black grapes, and these components are best extracted during (and sometimes after) alcoholic fermentation.
The main components of wine
Wine is composed of a vast array of complex and delicate molecules, which explains in part why the world of wine has so much variety. It is nevertheless possible to identify the main components of wine. These are derived from the raw material, i.e. the grapes, and from the wine-making process. It is important for these components to be in balance.
The main components are water and:
Next to water, alcohol is the major constituent of wine. Alcohol is produced when yeast converts the sugar in the juice of ripe grapes. Carbon dioxide gas (CO2) is produced as a by-product (this is where the bubbles come from in sparkling wine). This conversion process is called alcoholic fermentation. It is represented in this simple equation:
Yeast + sugar = ethyl alcohol + carbon dioxide
Alcohol is the component in which all the flavours are dissolved. Wine releases so many aromas because alcohol evaporates very quickly, carrying the wonderful smelling components out of the glass.
When we talk about the body of a wine, we are generally describing the alcoholic strength, which varies from light (8% alcohol by volume) to heavy (15% alcohol by volume). This is because alcohol is much more viscous than water and so contributes to the sensation of 'weight' or fullness in the mouth. Dry wines high in alcohol also seem sweeter than dry wines low in alcohol.
Acids are essential to the flavour of wine and to its freshness. When we talk about balance in a wine, we are often referring to its relative levels of acidity and sweetness. Without sufficient acidity, a wine will taste 'flabby' and unattractive; with too much acidity, a wine will taste very tart, giving the same sensation in the mouth as sucking a lemon. The acids also act as a preservative to the colour and the fruit, helping the wine to stay fresh and, where appropriate, age properly.
There are many different sorts of acid present in wine, but there are three important ones: tartaric, malic and lactic. Tartaric and malic are constituents of grape juice. Lactic and other acids are produced during both alcoholic fermentation and malolactic fermentation.Tartaric acid is the most abundant and neutral-tasting.
Malic acid is also found in apples (malum is Latin for apple), which is why it often contributes a green-apple flavour to wine. Ripe grapes tend to have less malic acid than unripe ones. It is more aggressive than tartaric acid and rather like biting into a bramley apple.
Lactic acid is also found in yogurt and cheese. It has a much smoother, more rounded flavour, though wines very high in lactic acid can smell or taste slightly cheesy.
Tannins come mainly from grape skins but also from grape stems and from oak barrels used in the maturation of some wines. Grape pips contain bitter tannins, which need to be avoided in wine-making. Because white wines are usually fermented without the skins, tannins are much more significant in red wines.
Tannins are responsible for the chalky, mouth-puckering sensation that you sometimes get in young red wines, especially those produced in a cooler climate or from black grape varieties with thick skins such as Cabernet Sauvignon. This is known as astringency. You can experience the sensation of tannins by tasting very strong black tea. High tannin levels in a wine can make it taste bitter, especially if the tannins are not fully ripe.
Wines where the tannins are very noticeable are often described as dry, but they should be called tannic. If the tannins are ripe, they will soften and mellow with age. Tannins play a very important part in the structure of wine.
If white wines do contain some tannins from the grape skins, the wine is usually described as astringent rather than tannic.
During the fermentation process, yeast feed on the sugars in grape juice to produce alcohol. A wine in which all the sugars have been converted to alcohol is described as dry.
The sweetness in off-dry, medium and sweet wines can be achieved in two main ways.
Fermentation may stop naturally or be arrested artificially before all the sugars have been converted to alcohol. Fermentation stops naturally when the sugar or alcohol levels are so high that the yeast dies. Fermentation may be arrested artificially by filtering out the yeast or by adding spirit, for example. This sweetness is referred to as residual sugar, often abbreviated in technical notes to RS. The sweetness in port, for example, is due to the addition of spirit part-way through fermentation.
Alternatively, in some wines it is permitted to add unfermented grape juice (from the same origin and vintage) or concentrated grape must to the wine to sweeten it after fermentation. Many inexpensive German wines such as Liebfraumilch are made in this way.
In cooler climates where it is harder to ripen grapes and get high enough sugar levels, sugar may be added to the juice before fermentation but this is to increase the final alcohol level and not to sweeten the wine. This process is known as chaptalisation.
The grape is a fruit, with an unusually complex balance of delicate ingredients. It appears unique in its ability to mimic the smells and flavours of other fruits, depending on how and where it is grown. In warm climates such as California's Central Valley, a versatile variety such as Chardonnay can evoke smells of pineapple, mango and other exotic aromas. In the much cooler French region of Chablis, the same variety smells steely and austere, rather like wet stones, with flavours ranging from citrus to apple.
Wine would not be as popular as it is today without this wide range of fruit aromas and flavours. It is certainly possible to find other aromas and flavours such as tar, flowers and nuts but few wines are attractive if such scents and tastes are not allied to a recognisably fruity quality.
The juice of most grape varieties is colourless. The colour of young red wine is derived mainly from the anthocyanins in the skins. These compounds are extracted from the grape skins during the wine-making process.
As wines age, the colour changes, with red wines changing from ruby or purple to a softer brick red and eventually to brown. White wines tend to get darker with age, changing from water white to golden.
Wine is also rich in minerals and proteins. Minerals such as potassium and calcium are picked up from the soil by the vine roots and interact with the acids to influence the taste of the finished wine. Proteins are derived from the grape pulp and can cause problems by making the wine cloudy if they are not treated appropriately.
Oak is not really a component of wine but the use of oak in wine-making can significantly alter the flavour of a wine.