Definition - What does Sussreserve mean?
Süssreserve translates from German as "sweet reserve". This is a wine which is made by the hand-selection of an unfermented grape juice. It must be pasteurized or free of microorganisms. The juice is added to a still wine as a natural sweetener. It is a method practiced in Germany for semi-sweet wines made with Riesling.
WineFrog explains Sussreserve
Süssreserve is a special semi-sweet wine made by adding grape juice to a still white wine, typically of the same varietal. By adding the grape juice, the sugar content increases, but the alcohol also decreases. Under German law, no more than 15% of the overall volume can be from the selected juice.
This is a practice which is done for many German wines and is also permitted for Prädikatswein. However, it is typically only reserved for Kabinett and Spätlese wines.