Weisse is different from other German beers. It stands out with bold, yeasty flavors that would be considered off-flavors in a typical lager.
The activity of the yeast in a hefeweizen brings out phenolic flavors such as fruity bananas and spices like cloves. It even hints of bubblegum. Unlike IPAs, these unusual flavors are not derived from hops, but totally from the yeast. The hopping is quite low, with only 9 IBUs in Göller's Steinhauer Weisse.
The phenolic flavors expected in a Weisse are released only when the wort brews for a time at between 105º and 113ºF. This practice is known as a ferulic rest (releases ferulic acid). This acid is what gives the German Weisse its unique taste.
Here is the science behind the Phenolic taste. Yeast: Torulaspora delbrueckii. This top-fermenting yeast produces phenols and esters that impart banana, bubblegum, nutmeg and clove flavors. Yeast has very low flocculation qualities, leaving the finished beer cloudy. Attenuates at over 80%, leaving a dry, crisp beer. Clove Flavor: Result of the phenol 4-vinyl guaiacol, a metabolite of ferulic acid, metabolized by the yeast. Banana Aroma: Derived from the ester called Amyl Acetate, also released by the yeast. A true German Hefeweizen is also nothing like American wheat beer, which was invented in the 1980's. American ale focuses more on a bready and fruity flavors, lacking all the strange yeastiness and citrusy esters of a Weisse. Furthermore, most American wheats include fruits and other adjuncts not to be found in traditional German beer.
Weisse is an ancient beer, inherited from the days when brewers had primitive tools to make beer. To this day, Weisse is brewed according to the most ancient practices of top fermenting and triple decoction mashing that bring out these wild flavors.