Rieslaner is a cross of Silvaner and Riesling that was first bred in Veitshöcheim, Franken/Bavaria, in 1921 by the grape breeder August Ziegler. It is a late-ripening grape that is high in acidity.Today it is mostly grown in the Franken and in the Pfalz (Palatinate) regions, and the grape is often affected by botrytis. Rieslaner was bred to do particularly well with botrytis, and therefore it holds great potential to form an acidic, fruity, and full yield when it is ripened.
"Beerenauslese" is in fact a very similar quality as compared to "Eiswein" ("ice wine"), as it is typically harvested in late autumn (this wine was harvested 23rd Nov 2013), at a time when the first frost arrived, and grapes are individually hand picked!
The sugar content of Beerauslese and ice wine in Germany must be above 110 degree "Oechsle", which would corrrespond to unbelievable >300 g per liter of sugar! Of course, the wine after fermation has a much lower sugar content, but still 182.8 g/l. Since the wine has a relatively high acidity, part of the sugar is "masked" by this acidity.
For comparison and to put this in relation to other sweet drinks: most Sauternes have around 150 g/l residual sugars, and the sweetest wines in the world have sugar contents up to 900 g/l (hard to believe and very close to the physical limit of sugar solution in water, but true: http://www.winespectator.com/webfeature/show/id/46651). Coke contains quite substancial 106 g/l sugar, again "masked" by its high acidity
More to read about this interesting topic of sugar content in German wines:
This 2013 Rieslaner Beerenauslese shows a fine fragrance, a good sweetness, and an opulent peach and tropical fruit nose. It fits well with sweet/chocolate deserts, or with tropical fresh cut fruits.
Residual sugar: 182.8 g/l
Acidity: 14.0 g/l