Spreewald gherkins (German: Spreewälder Gurken or Spreewaldgurken) are a specialty gherkin from Brandenburg, which are protected by the EU as a Protected Geographical Indication (PGI).The secret of the Spreewald gherkins' special taste remained hidden, even to the satirist Fontane. Certainly, the moist soil, rich in humus, and the climate in the Spreewald also contribute to the good growth in the cucumber fields. The actual reason for the taste, which is considered by connoisseurs to be delicate, is found in their processing. While the process of fermentation in large barrels formerly took several weeks, gherkins today are ready for sale after only one day of processing—whether for mustard gherkins (Senfgurke), gherkins or dill pickles (Gewürzgurke) or pickled cucumbers (Salzgurke). This enormous time saving is achieved by heating to 70 °C (158 °F) with the addition of caustic soda. The composition of the additional ingredients, however, still remains a well-guarded secret of the approximately twenty picklers. These taste-enhancing ingredients, such as basil, lemon balm, grape leaves, cherry leaves or walnut leaves, give Spreewald gherkins their special sour, spicy taste.