There are some classic styles of dessert wine that are appellation-specific and many proprietary dessert wines that emulate these classics or are otherwise unique. Classic-style dessert wines include Moscato, Port, Sauternes and sweet styles of Sherry, along with Asti Spumante, Ice Wine, Madeira, Passito, Tokay and other possibilities. There are several different methods, practices or techniques used to accomplish these two requirements.
Natural sweetness  In the absence of the techniques described below, makers of dessert wine have to produce their sugar in the vineyard. Some grape varIetals, such as Muscat, naturally produce a lot more sugar than other varietals. 
Late harvest  Grapes are allowed to over ripen and reach high level concentrations of sugar by delaying harvest. Sauternes are made in this manner in Bordeaux as are dessert wines produced in the Loire Valley, particularly from Chenin Blanc, and in Alsace using several varietals. Many late harvest wines are also made in both Australia and the United States.
Dried grapes  Besides extended ripening, other means are used to concentrate grape sugars. Grapes may be allowed to partially raisinate, either before or after harvesting. Normally-ripened grapes can be harvested, then spread on reed mats or paper trays to dry in the sun or the bunches are tied along rafters. The length of time needed can vary from three weeks to four months, depending upon the grape varietal, the type of wine being made and the weather conditions at the drying location. This partially dried fruit may be fermented on its own or added to base wine made from normally-harvested fruit. This technique, called passito, evolved in Greece and dates back to the 8th century B.C. Today the technique is used primarily in Italy in the making of Amarone and Recioto in Veneto and Vin Santo in Tuscany.
Fortification  Many dessert wines get most of their alcohol by fortification, that is, by having distilled spirits added rather than creating it naturally by fermentation; however, not all fortified wines are sweet. Using this technique, grapes are allowed to begin fermentation; then distilled spirits are added to raise the level above yeast tolerance, thereby stopping fermentation and retaining the remaining sugar. Port, Sherry, Marsala and Madeira are all made by fortifying partially or completely fermented must. Depending upon the region and style, the wines may then be further aged, blended, sweetened or treated in some manner according to traditional practices that give that product its unique consumer appeal.
Ice wine  Grapes used for ice wines freeze at the end of harvest and, because of this, they yield only a small amount of sugary juice when they are pressed. Ice wines are produced in cold regions, such as Canada and Germany. Ice wines are often best without food; however, ice wines are best if consumed with food, desserts without milk or dark chocolate that are less sweet than the ice wine. If consumed with food, ice wines pair with apple pie or fritters, oysters, pate, peaches, pears and strawberries.
Noble rot wine  Some of the most famous dessert wines, such as Chateau d'Yquem, are made from mouldy grapes, but not just any mould. Botrytis cinerea acts by sucking water out of the grape while imparting new flavors of honey and apricot into the future dessert wine. Unfortunately, however, this fungus is very fussy about conditions required for such noble rot: if conditions are too damp, the same fungus causes the destructive grey rot. Typically, noble rot forms best in conditions where morning mist from a nearby lake or sea gets burned off during the day by hot sun. 
The general rule is that the dessert wine should be sweeter than the food it is served with, such as a perfectly ripe peach, but not with many chocolate and toffee-based desserts. Quite often, the wine itself can be a dessert, but bakery sweets can make a good match, particularly with a little bitterness like almond biscuits (such as biscotti) dunked in Vin Santa. White dessert wines are generally served somewhat chilled, while red dessert wines, as a rule, are served at room temperature or slightly chilled.
Cheeses that go well with dessert wines include Asiago, Beaufort, blue cheeses, Brie, Cabrales, Cheddar (sharp and smoked), Comte, Emmnental, Fontina, Gorgonzola, Gouda, Gruyere, Limburger, Manchego, Mahon, Mascarpone, Meunster, Monterey Jack, Parmigiano-Reggiano, Provolone, Roquefort, Stilton, certain sheep-milk cheeses, such as Pecorino Romano and Pecorino Toscana and such washed-rind cheeses as Taleggio from Italy, Cowgirl Creamery's Red Hawk, and Reblochon, Pont-L'Eveque and Livarot from France.