Wild Yeast

While wild yeast is sometimes intentionally catered for and wanted (see brett), there are several species that can negatively affect beer.

Among non-Saccharomyces wild yeast, those such as Pichia, Rhodotorula, Kluyveromyces, and Candida can negatively affect the quality of beer by causing haze or a film on the surface. Additionally, they may produce off-flavors such as diacetyl or phenolic compounds.