Hefeweizen is a German style of wheat beer in which the yeast is not filtered out. Though Kristallweizen (clear), Dunkelweizen (dark), and Weizenstarkbier or Weizenbock (higher alcohol content) varieties are available, they are not considered true hefeweizen unless left unfiltered. The filtration which takes the yeast out of Kristallweizen also strips the wheat proteins which make Hefeweizen cloudy. Alternate terms for hefeweizen include: Hefewei?bier, sometimes Wei?bier, Hefewei?e, Weizenstarkbier (not necessarily a hefeweizen unless left unfiltered) The hefeweizen style is particularly noted for its low hop bitterness (about 15 IBUs) and relatively high carbonation (approaching four atmospheres), considered important to balance the beer's relatively malty sweetness. Another balancing flavor note unique to hefeweizen beer is its phenolic character; its signature phenol is 4-vinyl guaiacol, a metabolite of ferulic acid, the result of fermentation by ale yeast appropriate for the style. Hefeweizen's phenolic character has been described as "clove" and "medicinal" ("Band-aid") but also smoky. Other more typical but less assertive ale flavor notes include "banana" (amyl acetate) and sometimes "vanilla" (vanillin). Some prominent commercial examples of hefeweizen are produced by Paulaner, Erdinger, Schneider Weisse (original amber only), Franziskaner, Rothaus, Hacker-Pschorr, Ayinger (Br?u Weisse) and Weihenstephan. The style is a favorite throughout Germany, but is especially in Bavaria and across Southern Germany.