Rotberger is an interesting grape, hardly if ever found in the United States in either plantings, or even in imported wines.

Certainly the ancestry of the grape traces partially (not fully) to Riesling and reportedly is also part Trollinger.  These are wines which mature early and as you might expect with Riesling as a parent, highly acidic especially for a red wine.

Outside of Germany, a small amount of the wine is grown in Canada and Germany's neighbor Austria.