An old, rare and unique German beer style, Kellerbiers are unfiltered and unpasteurized lagers that date back to at least the Middle Ages. The beer is matured, unbunged and unprotected from oxygen, in deep vaults. The final product is a smooth, naturally cloudy beer that’s rich in vitamins from the yeast. Hop bitterness can be high and alcohol will vary. Zwickel Bier is similar to a Keller, but not as pronounced.