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[[File:Brussels brett blend pellicle1.jpg|thumb|Pellicle from The Yeast Bay Brussels Brett Blend; courtesy of Dan Pixley]]
A '''pellicle''' is a type of [[Quality_Assurance#Biofilms|biofilm]] which appears on the surface of beer (the classification of pellicles as a type of biofilm has recieved some debate. See [[Pellicle#Scientific_Terminology|Scientific Terminology]]). It consists of an aggregation of cells, proteins, and polymers <ref name="Branda"></ref><ref name="matt"></ref>. The "bubble" formations are caused by trapped CO2 beneath the pellicle film. Pellicles are often formed by ''[[Brettanomyces]]'', ''Acetobacter'' <ref name="Perumpuli">[http://ir.kagoshima-u.ac.jp/bitstream/10232/21479/4/Diss_Perumpuli+Arachchige_Buddhika+Niroshie_RNK999_2014.pdf.pdf Pellicle of thermotolerant Acetobacter pasteurianus strains: Characterization of polysaccharide and induction patterns. Perumpuli Arachchige Buddhika Niroshie. 2014-09-30.]</ref>, and other gram-negative bacteria such as some species of ''Acinetobacter'', ''Escherichia'', ''Burkholderia'', ''Dickeya'', ''Gluconacetobacter'', ''Pseudomonas'', ''Salmonella'', ''Shewanella'', and ''Vibrio''. Gram-positive bacteria ''Bacillus subtillis'' can also form a pellicle <ref name="Armitano">[http://www.ncbi.nlm.nih.gov/pubmed/25756106 Gram-negative bacteria can also form pellicles. Armitano J, Méjean V, Jourlin-Castelli C. Environ Microbiol Rep. 2014 Dec.]</ref>. It can also be formed by ''[[Saccharomyces]]'' in rare occasions (most likely wild species more so than brewer's yeast), and it might be possible for ''[[Lactobacillus]]'' and ''[[Pediococcus]]'' to form a pellicle (according to Dr. Matt Humbard; see referenceand [https://www.facebook.com/groups/MilkTheFunk/posts/8967638479930953/?comment_id=8967994039895397 this opinion piece by Dr. Bryan Heit on MTF on why it is difficult to find any scientific sources for pellicles]); however, however other references have this has not been found scientifically proven as far as we know <ref name="matt">[http://phdinbeer.com/2015/01/30/beer-microbiology-what-is-a-pellicle/ Beer Microbiology – What is a pellicle? A PhD in Beer blog. Dr. Matt Humbard. 01/30/2015. Retrieved 04/26/2015.]</ref>. Pellicles are not formed by and should not be confused with [[mold]].
==Characteristics==
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===
We may also be able to glean some insight from studies done on ''Acetobacter'' pellicle formation during vinegar production.