Zwickl lagers, or kellerbiers, refer to unfiltered lagers and range widely in color, averaging between 4.5-5.5% in alcohol with variations depending on the interpretation of the style. Kellerbiers are essentially unfiltered versions of traditional German-style lagers. Traditional kellerbiers are less carbonated and may contain subtle sulfur and acetaldehyde aromas and visible yeast sediment. Contemporary versions of kellerbiers are very similar to traditional versions except that most examples are fully carbonated and the acetaldehyde aromas are absent due to being fully lagered. Noteworthy examples of this style include: Samuel Adams Alpine Spring, Urban Chestnut Zwickl and Stiegl Paracelsus Zwickl. (Beer/Classification & Attributes)