Actually, sweet wines aren’t really all about just desserts. Sweet wines can make an appearance at many stages of a meal, and also sometimes just for sipping.

Before we go any further, let’s be clear that there are two aspects of a wine that might be called sweetness. First is the actual sugar in the finished wine, called Residual Sugar and which is technically measurable in grams per litre (g/l). Pretty well everyone would call a wine with only single-figure g/l dry… beyond that it gets complicated (though most “sweet” wines are 45 – 200 g/l)… That is because there is a second aspect to sweetness: the overall impression of the finished wine. This may be very different because of the level of acidity in the wine. A wine with quite a lot of Residual Sugar and very high acidity may seem drier than a wine with (say) only half the sugar but much lower acidity. In fact, I would go further and say that the higher acidity wine will seem fresher, less cloying, less sweet, more food friendly and all round just better than the lower sugar wine.

This is the key really – good sweet wines tend to have good counterpointing acidity. The sort of thing one expects from high acid grapes: Riesling, Chenin, Semillon… and unsurprisingly these are the base grapes for the most highly regarded sweet wines…

All wine making starts with a grape juice (called must) with significant levels of sugar – maybe 210 g/l – which is converted to alcohol by fermentation. For normally harvested grapes, by the way, this will be more or less equally glucose and fructose. Late Harvest grapes have more fructose – which appears sweeter (and fruitier!) to the palate.

So immediately there are two ways of making sweet wines. One is to stop the fermentation before all the sugar is converted to alcohol, the other is to start with more sugar in the juice.

The first group – wines with arrested fermentation – includes Muscato d’Asti, Traditional German Rieslings, Vins Doux, Ports, Madeira and similar wines. In the first two cases the fermentation is stopped by chilling: a deliberate choice nowadays but originally a natural impact of cold winter climates in German vineyards. More common is stopping the fermentation by increasing the alcohol (yeast can’t live above about 15% abv) by dosing the mixture with grape spirit or brandy. Most wines made this way use a neutral alcohol so the flavour is determined by the original grapes.

The second way of making sweet wine is to start with more sugar in the must than can be fermented to alcohol. This can be done in a variety of ways, simple later harvesting will yield higher sugar (especially fructose) levels. If one waits until the grapes start to dry out on the vine, even more sugars will exist relative to the volume of juice. One could go even further and let the grapes freeze – which has an even more pronounced effect. In addition one could replicate these effects off-the-vine, drying picked grapes This is often done on straw mats, either for a few days in the sun, or over winter in airy buildings. The method is common in Mediterranean climes specially Italy where it is called Passito. One could even freeze picked grapes, an example is Bonny Doon Vin de Glaciere, made by Randall Grahm freezing Muscat grapes (It’s about £18 for ½btl). Of course any of these methods can also be combined with stopping the fermentation at a certain point.

However the most famous method of arriving at concentrated sugars is from the action of Botrytis Cinerea, or “noble rot”. This is a fungus that can attack whole bunches of grapes in continually damp conditions, causing loss. But if it takes hold on individual berries and there is a dry period after infection the fungus consumes the water and concentrates everything else in the grape, including sugars and acid. Most great sweet wine – Sauternes, Bonnezeux / Quarts des Charme / Vouvray in the Loire, some German sweet wines, Tokaji, some Muscat based wines – are produced using Botrytis affected grapes. In the cases cited above, the grapes will be Semillon, Chenin Blanc, Riesling and Furmint.

Botrytis does have a flavour impact on the wine – notes of marmalade and honeysuckle are often cited – with a warm slightly bitter note on the palate too, which echoes the marmalade reference.

However the best examples keep the balance between the Botrytis and the natural flavours of the grape – producing (e.g.) butterscotch with Semillon, passion-fruit with Chenin…

This month we’ll have 2 arrested fermentation wines, together with wines that combine approaches and a couple that are Botrytis dominated. Notes of those wines will appear in 3 or 4 days….

Until then…