Sweetening of wine can be carried out by the addition of grape must (unfermented grape juice, also known as sweet reserve or Süss-reserve), but not by the addition of sugar. Concentrated grape must or rectified concentrated grape must may be used if a wine has not been enriched.
Süss-reserve is permitted to contain up to 1.0 %vol alcohol.

There are European Commission legal requirements for addition of Süss-reserve:-

1) For wines which have been enriched:

- that there should be no increase in the 'total' alcoholic strength of the wine.

For example, if the grapes were harvested at 69 °Oechsle (9.1 %vol alc) and sugar was used to enrich the must to 84 °Oe (11.4 %vol alc) then legally any Süss-reserve added should have a must-weight of not more than 84 °Oe. For any English or Welsh Wines with grapes harvested at below 61.5 °Oe (7.9 %vol alc), enriched by 3½ %vol, it would be technically illegal to use 84 °Oe Süss-reserve.

2) For wines which have not been enriched:

- the 'total' alcoholic strength of a wine may be increased by up to 2 %vol.

However, with German QmP wines, when sweetening a Spätlese it would be illegal to add a lower °Oe Kabinett Süss-reserve.

3) For Quality Wine the addition of sweet reserve is restricted to products originating in the same Quality Wine region.

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