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http://en.wikipedia.org/wiki/Eiswein
Ice wine (or icewine or, in German, Eiswein) is a type of dessert
wine produced from grapes that have been frozen while still on the
vine. The sugars and other dissolved solids do not freeze, but the
water does, so the result is a concentrated, often very sweet wine.
The effect is comparable to the freeze distillation that was
traditionally used to make applejack and similar beverages, but in
the case of ice wines, the freezing happens before the
fermentation, not afterwards. Unlike the grapes from which other
dessert wines (such as Sauternes, Tokaji, or Trockenbeerenauslese)
are made, ice wine grapes tend not to be affected by Botrytis
cinerea or noble rot. This gives ice wine its characteristic
refreshing sweetness balanced by high acidity. When the grapes are
free of Botrytis, they are said to come in "clean".
