Eiswein—German for "ice wine"—is a category of wine defined by German wine law. Eiswein is made from grapes that are very high in natural sugar content, but aren't concentrated through the effect of Botrytis cinerea. They derive their sweetness from grapes freezing on the vine in November or later (hence the name). The sweet grape juice is separated from the frozen water molecules during early morning pressings of the frozen berries, resulting in wine that is high in acidity and residual sugar (and highly sought after).