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Winemaking

Making Sweet Wine

  • Practically every winemaking region in the world has its own style of dessert wine and there are many different methods used to produce them. Wine is sweet either because some of the natural sugar from the grapes is retained by stopping fermentation early or because sugar is added to the wine after fermentation.

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  • The first step in producing sweet wine is obtaining grapes with high sugar levels. One way to do this is to simply leave the grapes on the vine until the sugar reaches the desired concentration. This method can be referred to as late harvest, vendange tardive, spätlese, auslese, etc., depending on where the wine is produced.

    Another common method in harvesting grapes with high sugar levels is to allow a fungus called botrytis cinerea, or "noble rot," to attack the grapes. This fungus pokes holes in the skin of grapes, which allows water to evaporate and concentrates the sugars inside the berries. Botrytis adds a distinctive aroma and flavor to the wine and increases its viscosity. Botrytis is common in the production of Sauternes and the sweet Chenin Blanc wines of the Loire (Bonnezeaux, Quarts de Chaume, Vouvray Moelleux) amongst others.

    A third way to concentrate the amount of sugar is to harvest after the grapes have frozen when temperatures in the vineyard drop below freezing. When the bunches are pressed, the sugar concentration in the must is quite high because all of the water in the grapes is frozen. This method is used in the production of Eiswein. This effect can be reproduced by freezing grapes, a process called cryoextraction.

    For wines like Amarone, Vin Santo and Vin de Paille, grapes are slowly dried in order to concentrate sugars.

    And finally, some winemakers raise sugar levels by simply adding sugar 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.

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  • Sometimes fermentation in sweet wines ceases naturally because the alcohol reaches a level that kills the yeast. In most cases residual sugar remains because the fermentation was stopped early. This is often accomplished by adding sulfur. Other means of arresting fermentation include refrigeration, filtration, pasteurization and applying pressure.

    Another common method of stopping fermentation is called fortification in which neutral alcohol (either grain or grape) is added to the wine. This method is used for the production of Port, Muscat Beaumes de Venise, Muscat from other regions, Banyuls, Maury and other Grenache-based wines from other regions.

    In Sherry production, the wine is fortified after it has been fermented to dryness. Sugar in the form of sweet wines made from the Pedro Ximenez grape is added back into the wine. Other examples of wines that are sometimes sweetened after fermentation include Champagne and German Riesling.

    Once fermentation has ceased, it is important to ensure that the wine does not begin to ferment again. This is done by removing the yeast by sterile filtration, pasteurizing it, or treating it with chemicals such as sulfur dioxide and sorbic acid.

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