The tannic content of a wine sometimes makes wine seem unappealing or even unapproachable to those new to the drink. Tannins, derived from the skins, stalks and pips of grapes, are instrumental in the ageing of wine: They act as a natural preservative. As the Tannins soften and fade over years, the developing flavours they have preserved will become accessible.
Tannins also give structure and backbone to the wine, which is an important feature as of itself. A level of tannins that is sufficient to provide structure and coherence, but not so obvious as to dominate the palate with their astringency, signifies when the wine is in its ideal drinking phase. Tannins are far less important in the ageing of white wines.
In wine tasting, acidity refers to the fresh, tart and sour attributes of the wine which is then evaluated in relation to how well the acidity balances out the sweetness and bitter components of the wine.
Certain acids, such as acetic acid, are known as volatile acids and in small amounts can enhance the flavours of the wine and bring them into focus. In larger amounts the wine will result in a wine fault – unless you happen to enjoy the overpowering taste of vinegar or nail-polish remover.
Natural acidity is highest in cooler regions, such as Champagne, Burgundy, England, New Zealand, Germany, Canada and so forth. Low acidity is found in warmer climates, such as Australia’s (where in certain regions chemical acidification is required).
Alcohol is produced by the fermentation of sugars by yeast, and so it follows that the higher the sugar level in the grapes, the higher the final alcohol level in the wine when it is fermented to dryness. Sugar accumulates in grapes during the ripening process, being produced by the process of photosynthesis in the leaves and stems of the grapevine.
The rate of photosynthesis is determined by the intensity and duration of light, plus the ambient temperature, in a rather complex relationship. In brief, photosynthesis is maximised in warm, sunny conditions where there is lots of light and the elevated temperatures cause chemical reactions to occur at a faster rate, but if it is too hot, photosynthesis stops because the vine closes its stomata (gas exchange pores) to reduce water loss. Thus we can have a situation where in hot regions, development lags behind warm regions because photosynthesis will have ceased during the warmest hours of the day.
In Germany, where vines struggle to ripen, alcohol levels will be at about 7 or 8 per cent. In warmer climates the final alcohol level is determined not by the sugars, but by the yeasts themselves. Once the alcohol level reaches 14 per cent the yeasts can no longer function and will rapidly die off. Any wine with a strength of more than 15 per cent is almost certainly fortified.
Naturally, the process of fermentation is an important one; for this reason much attention has been lavished on it by the modern vigneron. Fermentation is exothermic, and so a cool, controlled fermentation will result in a radically different wine; fresh, delicate fruit flavours are protected by this method.
Given that fermentation is the conversion of sugars to alcohol, it follows that if fermentation is held up – either naturally or through artificial means – then more sugars will be left in the wine. There will always be residual sugar in the wine, no matter the style, and it is the amount left that determines the wine’s sweetness. This can range from 1 g/L of sugar (very, very dry wine) to as much as 250 g/L (Sauternes, Tokay sweet wine).
Wines are often subject to ‘oaking’, which confers aromas of vanilla, spice, caramel and toffee – though the aromas vary between American and French oak (though oak from the Balkans, once highly prized before communist rule, is making a comeback).
French oak tends to give mellower, buttery aromas whereas American oak has a stronger influence, with powerful vanilla and spice aromas. Of course, this is a rule of thumb and there are many different inputs and variables that can change the outcome (winemaking itself is far from a predictable or exact science). Variables include: how long the wine remains in oak, how much oak is used, how much of the oak is new as opposed to re-used, whether wine is aged or also fermented in oak, how the oak has been treated and whether or not barrels are used—as opposed to chips or powder (which are not necessarily legal or desirable).
Read more about Oak and Wine
The Noble Rot, for producers of sweet wine, is highly desirable and therefore encouraged. It usually only occurs in vineyards that lie next to large bodies of water, so that the morning mists dampen the grapes in the morning—Sauternes and Barsac being a fine example. These mists then disappear during the daylight hours, resulting in Noble Rot; should the mists persist, then it is the undesirable Grey Rot that will appear.
Make no mistake – grapes afflicted with Botrytis look terrible. They are discoloured and wilted, and give no indication of their winemaking potential. Nevertheless, when fermented they produce the most fantastic sweet wines in the world – the fungus dehydrates the grape, thereby concentrating the grape’s sugars. An obvious ramification is that quantity is therefore sharply reduced, which in turn results in much higher prices (you will often see botrytis wine sold in half-bottles, for that reason).
The result is a rich, luscious wine with concentrated, incredibly complex fruit flavours. These rank among the best of all wines and, although presently out of vogue, they are not to be overlooked by the true oenophile.