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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 they lack lactic acid. 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]].