Kellerbier, also Zwickelbier, is a type of Germanbeer which is often not clarified or pasteurised. Kellerbier can be either top- or bottom-fermented. The term Kellerbier literally translates as "cellar beer", referring to its cool lagering temperatures, and its recipe likely dates to the Middle Ages. In comparison with most of today's filtered lagers, Kellerbier contains more of its original brewing yeast, as well as vitamins, held in suspension. As a result, it is distinctly cloudy, and is described by German producers as naturtrüb (naturally cloudy). Kellerbier and Zwickelbier are often served directly from the barrel (for example, in a beer garden) or bottled.
Originally the term Zwickelbier, which is often used to describe a weaker and less full-flavored Kellerbier, was used to refer to the small amount of beer taken by a brewmaster from the barrel with the aid of a special siphon called the Zwickelhahn. Nowadays in Germany Zwickelbier is commercially available in large amounts, usually as a bottom-fermented, but often also as a top-fermented (Kellerweizen).