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: ''This article is about sour brewing methods using commercial cultures. For other brewing methods, see [[Brewing Methods]].''
'''Mixed fermentation''' (also referred to as "mixed culture fermentation") is any fermentation that consists of a combination of ''[[Saccharomyces]]'' (brewer's yeast), ''[[Brettanomyces]]'' (wild yeast), ''[[Lactobacillus]]'' (lactic acid bacteria), and ''[[Pediococcus]]'' (lactic acid bacteria), or other [[Nonconventional_Yeasts_and_Bacteria|microbes that are unconventional in brewing]]. Broadly speaking, there are two styles of mixed fermentations: mixed fermentations with lactic acid bacteria (''Lactobacillus'' and/or ''Pediococcus'') and mixed fermentations without lactic acid bacteria. Mixed fermentation sour beers are characterized by their higher acidity and tart flavor caused by the production of [[Lactic Acid|lactic acid]], and require the use of a lactic acid bacteria (abbreviated as '''LAB'''; generally ''Lactobacillus'' and/or ''Pediococcus''). These beers generally fall within a pH range of 3.0-3.7 (although [[Titratable Acidity]] is more accurate for measuring perceived sourness). Mixed fermentation without lactic acid bacteria are usually fermented with a combination of ''Saccharomyces'' and ''Brettanomyces''. Mixed fermentation beers without lactic acid bacteria may be slightly tart from the [[Acetic Acid|acetic acid]] production of ''Brettanomyces'', but are generally not considered to be sour if well brewed becaues because they lack lactic acidand too much acetic acid is considered a flaw. For both categories, the primary fermentation will be completed by yeasts such as ''Saccharomyces'' and/or ''Brettanomyces''.
This page will focus on information for mixed fermentation sour beers using pure laboratory cultures. For mixed fermentation beers without lactic acid bacteria, see the [[Brettanomyces and Saccharomyces Co-fermentation]] page. For 100% ''Brettanomyces'' fermentations (technically not a "mixed" fermentation), see the [[100% Brettanomyces Fermentation]] page. 100% ''Lactobacillus'' or ''Pediococcus'' beers do not exist because they do not fully attenuate wort (see [[Lactobacillus#100.25_Lactobacillus_Fermentation|100% ''Lactobacillus'' fermentation]] for details). Other alternative yeast and bacteria can also be used, however this is currently not common even for brewers who make wild/sour beers. For example, [[Spontaneous Fermentation|spontaneous fermentation]] and [[Wild_Yeast_Isolation#Growing_and_Testing_Without_Plating|wild yeast captures]] usually contain a plethora of [[Nonconventional_Yeasts_and_Bacteria|yeast and bacteria that are not conventional to modern brewing]].