It's hard to believe really. Wine with all its subtleties, nuances, and complexity begins with a grape.
A grape is 75 per cent pulp, 20 per cent skin and five per cent seeds. Pulp, the soft juicy center, is mostly water and sugar and small amounts of mineral, pectin and vitamins. Sugar is vital as it is converted to alcohol during the fermentation process. Skin is responsible for color, tannin, aroma and flavor while grape seeds contain tannin. Once winemaking is complete, the finished wine contains alcohol, acidity, tannin, dryness or sweetness and fruitiness.
Alcohol is a vital part of wines structure as it affects aroma, flavor and weight. During fermentation, sugar is converted to alcohol and glycerol, the latter of which contributes to sweetness and viscosity. The higher the alcohol content ,the weightier, more full-bodied, the wine. The aroma of high alcohol content is detected as a “burn” and, unfortunately, this aroma masks other, more desirable, aromas. Wines with high alcohol generally come from warm climates and fruit that is over-ripe or raisined.
Tannin – the “backbone” or “architecture” of wine, necessary for structure, age ability and as a natural preservative – is extracted from grape skins and seeds. It is detected by taste as bitterness and by feel as drying or astringent. The number of seeds, thickness of grape skin and size of grapes differ so certain grape varieties, such as Cabernet Sauvignon, Petite Sirah and Nebbiolo are high in tannins, while Pinot Noir, Grenache and Sangiovese are much less tannic varieties. When tannins are ripe the taste and feel is less notable, more integrated and softer than in wines with under-ripe tannins, which may be described as “grippy” or “rough”.
Acidity affects mouth-feel, age-ability, balance and flavour and is perceived as freshness, vigor, precision and clarity. Acid is a natural component in grapes. As grapes ripen, acidity decreases while sugar increases so winemakers aim to harvest when the grape is a perfect balance of sugar and acid. Wine without balance – too little acidity – is described as “flabby” or “syrupy” while those with excess acidity are found to be “harsh.” Fortunately for the winemaker and consumer, acid levels can be adjusted during winemaking by the addition of tartaric acid, an acid naturally present in grapes.
Grapes contain sugar that increases during grape ripening. Wine is referred to as dry when all grape sugars are converted to alcohol during fermentation while off-dry and sweet wines are those with residual sugar, meaning not all grape sugar is converted to alcohol. Certain wines need residual sugar for balance; wines such as German Riesling with its searing acidity. Winemakers aim for a balance between sugar and acidity in order to produce a harmonious wine.
Fruitiness is most apparent in youthful wines and those produced from fragrant grape varieties such as Muscat, Gewurztraminer, Riesling and Torrontes. Choosing to use aromatic yeasts during winemaking also plays a role. Ripe fruity aromas and flavours are often perceived as sweetness even in wine that is technically dry.