Editing Malolactic fermentation (section)

===''Pediococcus''===
[[File:Acrolein.svg|left|thumb|Acrolein taint is a common wine fault that undesirable species of ''Pediococcus'' can introduce to wine. Acrolein can interact with various phenolic compounds, imparting a bitter taste to the wine.]]
So far, four species from the genus ''Pediococcus'' have been isolated in wines and grape must, ''[[P. inopinatus]], [[P. pentosaceus]], [[P. parvulus]]'', and ''[[P. damnosus]]'', with the last two being the species most commonly found in wine. All ''Pediococcus'' species are Gram-positive with some species being micro-aerophilic while others utilizing mostly aerobic respiration. Under the microscope, ''Pediococcus'' often appear in pairs of pairs or tetrads which can make them identifiable. Pediococci are homofermenters, metabolizing glucose into a [[racemic mixture]] of both L- and D-lactate by [[glycolysis]].<ref name="Zoecklein"/> However, in the absence of glucose, some species, such as ''P. pentosaceus'', begin using [[glycerol]], degrading it into [[pyruvate]] which later can be converted to diacetyl, acetate, [[2,3-butanediol]] and other compounds that can impart unfavorable characteristics to the wine.<ref name="Wine Micro"/>

Most ''Pediococcus'' species are undesirable in winemaking due to the high levels of diacetyl that can be produced, as well as increased production of biogenic amines that has been implicated as one potential cause for [[red wine headache]]s. Many species of ''Pediococcus'' also have the potential to introduce off odors or other wine faults to the wine such as the bitter-tasting "acrolein taint" that comes from degradation of glycerol into [[acrolein]] which then reacts with [[phenolic compounds in the wine]] to produce a bitter-tasting compound.<ref name="Boulton"/>

One species, ''P. parvulus'', has been found in wines that have not gone through MLF (meaning malic acid is still present in the wine), but has still had its bouquet altered in a way that enologist have described as "not spoiled" or flaw. Other studies have isolated  ''P. parvulus'' from wines that have gone through malolactic fermentation without the development of off odors or wine faults.<ref name="Wine Micro"/>