A selection of sweets

Semillon grapes showing Noble Rot.

Who doesn’t like a sweet wine? OK, I have come across one or two obtuse individuals that claim not to have a ‘sweet tooth’ and abhor dessert wines, however on the most part a sweet wine will win anyone over. And they are so versatile. As long as the wine is sweeter than the food you want to pair it with, they go with a surprising number of dishes. The natural sugar in sweet wines can provide a perfect accompaniment to cakes, desserts and fruits, or a delicious foil to salty dishes such as parma ham or blue cheese.

Sweet wines come in many different forms. All the best examples contain what is termed ‘residual sugar’, that is natural sugar present in the grape that remains in the wine following fermentation. Cheap sweet wines typically have sugar added (‘back-blended’) to a nominally dry wine after the wine has been stabilised to avoid re-fermentation.

One of the simplest ways of producing a sweet wine is to dry the grapes. Dehydration removes some of the water in the grape, thus concentrating the natural fruit sugars. Drying can occur naturally on the vine (passérillage in French), thus grapes are ‘late-harvest’, or after picking by drying the grapes on straw mats or in special drying rooms.

Certain microclimates, notably in Germany and Canada, are perfectly suited for creating Icewine (or Eiswein in German). Grapes are harvested when frozen – usually in the middle of the night in the frigid depths of winter. While the water in the fruit is frozen, the sugars and other dissolved solids are still able to be pressed from the grapes, resulting in a very concentrated, sweet wine. Yields are tiny, thus icewine is a prized delicacy in some parts of the world.

A third way of producing sweet wines is to fortify them with a neutral grape spirit. This occurs for vin doux naturel such as Maury and Muscat, and for Port. The natural fermentation process is stopped by the addition of the spirit, thus leaving the remaining natural sugars unfermented. These fortified wines typically have alcohol levels in excess of 15% a.b.v. (Port is around 19-20% a.b.v.).

Perhaps the most intriguing method of producing a sweet wine is the enigmatic ‘noble rot. This rather bizarre term refers to a particular type of fungus (botrytis cinerea) that attacks the grape and dehydrates it, thus concentrating the flavours and the sugars. Rather convenient, although this parasite is hard to cultivate. It famously occurs in the Bordeaux appellation of Sauternes. The two rivers that enclose the region, the Garonne and the Citron, give rise to a specialised microclimate, creating misty early-Autumn mornings that encourage the botrytis fungus to grow, while the sunny afternoons complete the dehydration process. It is a dangerous business, as unwanted grey rot can just as easily form, ruining the grapes. Production is labour-intensive, with bunches needing to be picked by hand and inspected for the right sort of rot. Typically harvest proceeds over a long period of time as botrytis rarely affects the entire vineyard all at once. The risk of crop failure, the specialised microclimate required and the manpower required to harvest give reason to the expense of Sauternes.

The botrytis fungus provides its own aroma profile to a wine. I typically identify this as a sort of ‘antiseptic’ smell, although others have their own particular markers. The botrytis fungus also stimulates the production of glycerol in the grape, which increases its viscosity.

Outside Sauternes, botrytised wines can be found in Tokaji (Hungary), German Rieslings, the Loire, and some parts of the New World, where it seems to occur rather haphazardly (judging by the bottle of a one-off vintage of botrytised Gewurztraminer I picked up from Cloudy Bay in Marlborough recently).

The scale of sweetness can be measured quite scientifically, with the measure of grams of sugar per litre of wine, or g/L. Many wines described as ‘dry’ (i.e. not at all sweet) still have a few g/L residual sugar. In general, wines with around 40g/L could safely be described as ‘sweet’, although many of the greatest sweet wines have in excess of 200g/L residual sugar.

My next post will describe a few sweet wines tasted at a blind tasting recently.

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About James

James Flewellen is a biophysicist at the University of Oxford. He has competed for the University in international blind tasting competitions and won several awards. In addition, James is a wine educator and wine writer, most recently co-authoring "The Concise Guide to Wine and Blind Tasting". He also writes for the international gastronome site "The Rambling Epicure", and can be contacted for wine consultancy and educational courses through the "Oxford Wine Academy".
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2 Responses to A selection of sweets

  1. Pingback: A sweet wine tasting | The Oxford Wine Blog

  2. Pingback: Wines of Alsace | The Oxford Wine Blog

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