Sweet Wines

Table wines are generally fermented until they are dry: that is, until the yeast consumes essentially all the grape’s sugars and converts them into alcohol. Sweet or dessert wines with 10–20% “residual” sugar are made in several different ways:

• An ordinary dry wine is sweetened with some unfermented grape juice, and the combination treated to prevent further fermentation with a dose of sulfur dioxide, or filtration that removes all yeast and bacteria from the wine.
• Grapes are dried on the vine or after picking to concentrate their sugars to 35% or more of the grape weight. This leaves residual sugar in the wine when the yeasts reach their maximum alcohol level and the fermentation stops. German Trockenbeerenauslese and Italian recioto wines are examples.
• Grapes are left on the vine past the first frost and picked when frozen (or frozen artificially), and then gently pressed while cold to separate the concentrated juice from the ice crystals. The concentrated juice ferments into a stable wine with residual sugar. German Eiswein dates from around 1800.
• The grapes are allowed to become infected with “noble rot,” the mold Botrytis cinerea, which dehydrates the grapes, concentrates their sugars, and transforms their flavor and consistency. This method originated in the Tokaji region of Hungary around 1650, and was adopted in the German Rheingau by 1750 and in the Sauternes region of Bordeaux around 1800.