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[[File:Brussels brett blend pellicle1.jpg|thumb|Pellicle from The Yeast Bay Brussels Brett Blend; courtesy of Dan Pixley]]
==Characteristics==
===Introduction===
Pellicles presumably form when the surface of the beer is exposed to even small amounts oxygen <ref>[http://www.themadfermentationist.com/2009/11/brewing-sour-beer-at-home.html Brewing Sour Beer at Home. The Mad Fermentationist Blog. Michael Tonsmeire. 11/06/2009. Retrieved 02/28/2015.]</ref> Why microbes in sour/funky beer form a pellicle when exposed to oxygen is unknown. The most likely [http://phdinbeer.com/2015/01/30/beer-microbiology-what-is-a-pellicle/ hypothesis by Dr. Matt Humbard is that the formation of a pellicle] allows the organism (particularly ''[[Brettanomyces]]'', which prefers aerobic fermentation) to access the small amount of oxygen that is present in the headspace of the fermentation vessel. Another hypothesis, and one that may be less accurate according to Dr. Matt Humbard, is that the pellicle protects the beer from other microorganisms <ref name="matt"></ref>. Yet another hypothesis that is often cited is that the pellicle protects the beer from oxygen itself <ref>[http://jesterkingbrewery.com/pellicle-photos Jester King Blog on Pellicles. Retrieved 09/24/2015.]</ref>; however, however arguments evidence and rationale for this hypothesis are is lacking.
Popular thought is that the formation of a pellicle is not indicative of the quality of the sour beer that is being produced; it is only an indication that oxygen has entered the fermentation vessel and that the microbes are reacting to that exposure. One myth about pellicles is that the sour beer will be ready to package once the pellicle falls out; there is actually no correlation between the maturity of the beer and pellicle formation or dissipation. Some sour beers never form pellicles, and turn out fine as well, so the formation of a pellicle has no correlation with the quality of the beer.
See also;
* [https://www.facebook.com/groups/MilkTheFunk/permalink/2002649679763236/?comment_id=2002789613082576&comment_tracking=%7B%22tn%22%3A%22R%22%7D MTF thread speculating on the function of pellicles in Sherry Flor.]
===Yeast===
Pellicle formation by microbes found in sour beer such as ''[[Brettanomyces]]'' and ''[[Lactobacillus]]'' has not been widely studied. One report by De Roos et al. (2018) reported that in lambic casks that were studied, a pellicle formed at around 6 months into spontaneous fermentation. This pellicle formation was attributed to by ''Brettanomyces'' and oxidative yeasts, and this corresponded with a decline in acetic acid bacteria populations. The researchers hypothesized that the formation of the pellicle was the cause of the reduction in acetic acid bacteria populations <ref name="De_roos_AAB_2018">[https://journals.asm.org/doi/10.1128/AEM.02846-17 Temporal and Spatial Distribution of the Acetic Acid Bacterium Communities throughout the Wooden Casks Used for the Fermentation and Maturation of Lambic Beer Underlines Their Functional Role. ASM Journals. Applied and Environmental Microbiology. Vol. 84, No. 7. DOI: https://doi.org/10.1128/AEM.02846-17.]</ref>.
===Acetobacter===
''Acetobacter spp.'' produce homo and heteropolysaccharides (polysaccharides consisting of one type of sugar or more than one type of sugar, respectively <ref>[http://www.britannica.com/science/heteropolysaccharide Heteropolysaccharide. Encyclopedia Britannica. Retrieved 09/05/2015.]</ref>) that attach to the surface of the cells (capsular polysaccharides - '''CPS'''), as well as polysaccharides that are secreted into the medium in which they live (extracellular polysaccharides, or exopolysaccharides - '''EPS'''). CPS is the mechanism that allows pellicle formation in ''Acetobacter'' as the cells tightly associate to one another via CPS <ref name="Perumpuli"></ref>.
See also:
* [[Quality_Assurance#Biofilms|Biofilms]]
==Images==