Since 2010 this is also done at Schlenkerla: For all seasonal bock beers (currently Oak smoke Eiche double bock, Urbock and Lentbeer Fastenbier) there is a specially unfiltered and limited edition. These bottles are then lagered for at least 4 years in the rock cellars at the there natural temperature of around 8°C. The yeast continues to work during that time and constantly creates new flavors and aromas. A unique experience for all beer lovers!