Making Dessert Wine

For wine to be sweet, there must be a noticeable amount of sugar left in it after fermentation. This is known as residual sugar. The simplest method is to stop the fermentation before all the sugar has been turned into alcohol. This can be achieved by killing the yeasts with sulphur or removing them with a filter or a centrifuge.

The cheapest way of making a dessert wine is simply to add sugar. In the best cases this will be natural grape sugar, in the worst, cane sugar. Although these wines are sweet they are usually lacking in balancing acidity and interesting flavours.

Intense, sweet wines - notably Sauternes from Bordeaux in France - come from grapes affected by a fungus called noble rot or, more properly, botrytis. It's 'noble' because rather than ruining the grapes like any other disease would, it reduces their water content and concentrates the sugar and acidity. The fungus wraps itself around the grapes and spores puncture the skin. This draws off water, leaving the grape shrivelled but tasting delicious: full of the sugar and glycerine that was left behind. The wine is then made using the normal method for white wines, but the high sugar and glycerine content means that the wine is sweet, luscious and full-bodied. Because grapes high in natural acidity are used (Sauvignon Blanc, Sémillon,Riesling,Gewürztraminer) the wine is not at all cloying. Though sweet, the best wines are balanced and full of subtle flavours that linger on the palate.

An Italian technique is to leave the grapes to shrivel for several months after picking before making the wine. These wines are called passito or recioto.

A rare and expensive form of sweet wine is the icewine of Canada, or Eiswein of Germany and Austria. Here the grapes are left on the vine into the dead of winter - often into the new year. On a suitably cold night the frozen grapes are harvested and pressed. During both of these processes the temperature must not exceed -8 °C. The frozen water is driven out as shards of ice, leaving a highly concentrated juice, very high in acids, sugars and aromatics. From this, a wonderfully luscious and sweet wine is made.