Elements of Wine 3: Sugar
Wine Tasting with James Flewellen
As mentioned in my previous post on alcohol in wine, sugars accumulate in grapes as they ripen. At harvest time, grapes have a level of what is termed ‘potential alcohol’, that is the alcoholic strength of the future wine should all sugar in it be fermented to alcohol by the action of yeast cells. However, in some cases not all the sugar is fermented, leaving what is termed ‘residual sugar’ in the wine and a noticeable sweetness on the palate.
There are a number of ways to obtain sweetness in wine. The fermentation may be stopped deliberately, perhaps through addition of sulphur dioxide, which kills yeast, or through passing the wine through a membrane filter to remove the yeasts. This results in a wine of lower alcoholic strength and some residual sugar. A classic example is Riesling from the Mosel in Germany, which typically has 7-9% abv (Alcohol By Volume) and varying levels of sweetness depending on the initial level of ripeness of the grapes.
In other cases, there may be too much sugar for the yeast to convert it all to alcohol. Somewhere around 13-15% abv yeast stops being able to effectively ferment sugar to alcohol and naturally dies off. Super-ripe grapes will thus result in a wine with relatively high levels of alcohol and some residual sweetness. This sweetness can be quite subtle, or it can be syrupy and luscious – as found in dessert wines, which have very high concentrations of sugar in the harvested fruit.
Tasting sugar in wine is a difficult process. We can usually tell if something is ‘moderately sweet’; however it’s very hard to estimate the sweetness level in full-blown dessert wines. Wines with a little bit of residual sugar often have their sweetness masked by acidity and flavour compounds.
Sweetness in wine should be matched by a refreshing acidity for balance. This is especially true for dessert wines, which can come across as cloying without sufficient acidity. On the other hand, a touch of residual sugar, while not tasteable to most people, can give a welcome sense of roundness to a sharply acidic wine.
Sign up for Jonell Galloway and James Flewellen’s “Celebrate the Chartres Festival of Lights & Autumnal Equinox with a Food & Wine Tasting Masterclass” in France from September 19 to 22, 2013.
About James Flewellen
Dr James Flewellen is a biophysicist at the University of Oxford. James learned his trade in taste through the Oxford Blind Wine Tasting Society, of which he was the President from 2010-2012. During his term, he represented Oxford at many international blind tasting competitions – twice winning the prestigious ‘Top Taster’ Award in the annual Varsity blind tasting match against Cambridge University and captaining winning teams in competitions throughout Europe.
One of James’s goals is to clarify the complex and hard-to-navigate world of wine for both novice and experienced tasters. He applies his scientific training to wine education, illuminating concepts of taste, tannin and terroir in an approachable, entertaining manner. James runs wine education courses in Oxford through the The Oxford Wine Blog and is completing the WSET Professional Diploma in Wine and Spirits. He is the regular wine writer for The Rambling Epicure and is the founder of The Oxford Wine Blog. He is also currently co-authoring The Concise Guide to Wine and Blind Tasting – a book surveying the wine regions of the world and how to blind taste.