Trocken is German for dry, and is used in the classification of German wine. On a wine label, it indicates a wine that is dry rather than off-dry (halbtrocken), sweeter (lieblich) or sweet (süß). Technically, trocken wines are not devoid of residual sugar, but have, at most, a few grams per liter, which can be perceptible but is not overtly sweet. Trocken is also used as a designation for Austrian wine, but more rarely than in Germany, since many quality categories of Austrian wines are dry by default.
Somewhat confusingly, for Sekt and other sparkling wines, trocken indicates a higher level of sugar than it does for non-sparkling wines. A Sekt trocken is best described as off-dry or semi-sweet, while a Sekt brut is completely dry.
The maximum amount of sugar allowed for a trocken designation depends on the level of acid in the wine. For wine low in acid, a maxium of 4 grams per liter sugar is allowed. If the acid level exceeds 2 grams per liter, the sugar may exceed the acid level by 2 grams per liter, up to a maximum of 9 grams of sugar per liter. Most high-quality German white wines have a high enough acidity to be allowed up to 9 grams per liter of sugar under the trocken level. When used, the requirements in Austria are exactly the same.
Sparkling wines 
When used for sparkling wine, the term trocken actually means 17 to 35 grams per liter of sugar. This parallels the term sec ("dry") in French, which indicates a sparkling wine of the same sugar level as trocken. Drier wines are designated extra trocken at 12 to 20 grams of sugar per liter, while completely dry sparkling wines are given the designation brut (0–15 grams per liter) or extra brut (0–6 grams per liter).
Until the invention of sterile filtration, most German wines were dry. Fermentation continued until all the sugar was consumed, leaving only miscellaneous unfermentable sugars. Only the occasional sweet rarity, made from extremely ripe grapes, kept any residual sugar. For most of the twentieth century, the style was typically sweeter low alcohol wines. Only since about 1990 has dry, trocken wine become popular, partly because many prefer it with food. Most exported German wine is still of the sweeter styles. While it appears in the term trockenbeerenauslese, trocken in that case refers to the dried grapes, not the dryness of the resulting wine.
- Deutsches Weininstitut: Sparkling wine (Sekt), accessed on March 25, 2009
- Wines from Austria: Quality Designations in Detail, accessed on March 25, 2009