Sweetness is a spectrum
Riesling's biggest puzzle is sweetness, because it spans bone-dry to intensely sweet. The key is that sweetness is always balanced by high acidity, so even off-dry wines can taste fresh, not sugary.
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Clues to sweetness
Trocken = dry. Low alcohol (≈7–9%) often means residual sugar (fermentation stopped early); ≈11–13% usually means dry. Prädikat terms (Kabinett→Auslese) traditionally signal increasing ripeness, and often sweetness.