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| Grape growing, winemaking and wine maturation |
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| Making sweet wine |
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There are many types of dessert wine and several different methods of producing sweet wine. Wine can be sweet either because some of the natural grape sugar was retained by stopping the fermentation through one of several methods, or because the sweetness was added back to the wine after fermentation.
  The first step in the production of sweet wine is to obtain grapes with high sugar levels. One method is to simply leave the grapes on the vine until the sugar reaches the desired level. This method can be referred to as late harvest, vendage tardive, spätlese, auslese, etc.
Another common method is to allow the beneficent form of botrytis mold (botrytis cinerea, called noble rot) to attack the grapes. This degrades the skin of the grape, allowing water to evaporate, concentrating the other elements inside the berry. It also adds a distinctive aroma and flavor and increases the viscosity of the resultant wine. This is the method used in the production of Sauternes and the sweet Chenin Blanc wines of the Loire (Bonnezeaux, Quarts de Chaume, Vouvray moelleux) and other wines.
 A third way is to harvest grapes after they have frozen. This method traps the water as ice, and when the bunches are pressed, the sugar concentration in the must is much higher. This can be done when temperatures drop in the vineyard, or it can be done by freezing the grapes, a process known as cryoextraction. This is the method used in the production of Eiswein.
Sugars can also be concentrated by drying the grapes, as is done for Amarone, Vin Santo, Vin de Paille.
Finally, sugar can be concentrated simply by adding it to the fermenting must (chaptalization), or through the use of technology such as reverse osmosis, vacuum evaporation or spinning cone technology. These solutions are typically used for the least expensive sweet wines.
Sometimes the fermentation ceases naturally, either because the alcohol reaches a level that kills the yeast. In most types cases, however, residual sugar remains because the fermentation was stopped in some way. This is often accomplished by the addition of sulfur. Other methods of arresting fermentation include refrigeration, filtration, pasteurization and pressure.
Another common method of stopping fermentation is by the addition of neutral alcohol (grain or grape). This is known as fortification, and it is the method used for the production of Port, Muscat Beaumes de Venise (and Muscat in other regions), Banyuls, Maury (and Grenache-based wines from other regions, as well as other wines of this type.
In the case of Sherry, the wine is fortified after it has fermented to dryness, and sugar (in the form of sweetening wines made from the Pedro Ximenes grape) is added back to the wine. Other examples of wines that are sweetened after fermentation include Champagne and German Riesling.
Once the fermentation has ceased, it is necessary to ensure that the wine does not begin to ferment again. This is done by removing the yeast (sterile filtration), killing it (pasteurization) and/or treating the wine with chemicals such as sulfur dioxide and sorbic acid.
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Wine Regions of the World
