Term for an unfermented grape must made sterile by means of sulphur dioxide or filtration. This is added to already fermented wine, especially in cooler wine-growing regions, to soften the acidity and increase the residual sugar content. At best, the must is the same from which the wine was produced. Therefore, a portion is drawn off before fermentation begins, which must be sterile or completely free of yeasts in order to exclude secondary fermentation. It must be desulphurised before being added to the wine.
However, the term sweet reserve is also used for the process of sweetening itself. The required quantity can be calculated by means of Cramer's cross (see under blending cross) or (much simpler) by means of sweetening tables. In Austria, sweetening in any form (also by means of sweet reserve) is prohibited for the quality grade Kabinett and for all Prädikat wines. In Germany, the addition of sweet reserve is also permitted for Prädikat wines.
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