Bacteria are often lumped in with wild yeast as "spoiling" organisms for beer and other fermented beverages. However, some bacteria are also used intentionally, along with yeast, to create unique flavors in many beer styles, especially sour beer styles.
 Lactic acid bacteria
Some of the most commonly encountered bacterial strains in brewing are the so-called lactic acid bacteria, which contribute the sourness to many sour beer styles, as well as being responsible for the fermentation of cheese. Commonly encountered lactic acid bacteria include:
- Common cheese culture also used to add clean sourness to Berliner Weisse and other styles brewed with a sour mash.
- Another souring bacteria, used in lambics and other Belgian sour ales; it often also produces high levels of diacetyl.