Changes

to do: - https://www.facebook.com/groups/MilkTheFunk/permalink/3292440674117457/ [[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 long chain sugars (polysaccharides) formed on the surface of a beerpolymers <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]]'', [[Pediococcus]], and [[Lactobacillus]], as well as ''Acetobacter spp'' <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 Matt Humbard; see reference), however other references have not been found 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>. Note that "pellicles" in brewing have Pellicles are not formed by and should not been scientifically defined. See be confused with [[Pellicle#Scientific_Terminology|Scientific Terminologymold]] for more information.

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> One theory 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 theoryhypothesis, 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, evidence and rationale for this hypothesis 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. Another 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 fineas well, so the formation of a pellicle has no correlation with the quality of the beer. Another less common but occasionally discussed myth about pellicles is that sunlight might cause them. There is no evidence to suggest that sunlight has an effect on pellicle growth in beer. A more probable explanation for pellicles appearing in fermenters that have had sunlight on them is that when the sunlight hits the fermenter, the fermenter warms up. As it cools, a vacuum is created and air is sucked into the fermenter. Mark Trent demonstrates how readily air can suck into a fermenter when the fermenter is cooled (temperature shifts in general and atmospheric pressure changes can cause this): :<youtube height="200" width="300">aSgp0E96HCU</youtube> 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>.

Pellicle formation by microbes found in sour beer such as [[Brettanomyces]] and [[Lactobacillus]] has not been closely studied. However, we We may also be able to glean some insight from studies done on ''Acetobacter'' pellicle formation during vinegar production.

Pellicle formation in ''Acetobacter tropicalis'' has been linked to a gene cluster (polABCDE), and disruption of these gene switched the cells from producing CPS (and pellicle formation) to producing EPS instead <ref name="Perumpuli"></ref>..

The presence of ethanol in concentrations of 1-4% encourages pellicle production in some strains of ''Acetobacter pasteurianus'' (although the presence of ethanol encourages pellicle formation, the amount of ethanol did not make a difference). In some strains of ''A. pasteurianus'', sugar encourages pellicle formation. It has been suggested that CPS production in ''Acetobacter'' is a function of stress tolerance by acting as a barrier around the cell that protects it from acetic acid in the environment. Strains that form a pellicle in the presence of ethanol and/or higher temperatures can fully ferment vinegar whereas those that do not create a pellicle perform poorly in comparison <ref name="Perumpuli"></ref>.

==Scientific Terminology=Pellicle Appearance as a Microbe Identifying Indicator===As with some things in science that are not greatly explored, terminology isn't always agreed upon or fully established, and thus researching such a topic without a lot of prior knowledge can be challenging. Pellicles are a good example of this. It is sometimes stated that a pellicle is a type of biofilm. However, the widely accepted definition of a "biofilm" in biology, while very similar to a pellicle, refers to something specifically different. A [http[File://www.biofilm.montanaPichia_pellicle.edu/node/2390 biofilm] in microbiology is an aggregate of microorganisms where the cells adhere to each other on a solid surface <ref>jpg|thumb|[https://bookswww.googlefacebook.com/books?id=-ZDKAQAAQBAJ&pg=PT87&lpg=PT87&dq=brock+microbiology+biofilm&source=bl&ots=PwNZ20KFqq&sig=19lvlfqYj8bE7roiA7g4oJ3Xl0E&hl=en&sa=X&ved=0CCcQ6AEwAWoVChMImZaUmN_AxwIVVFmICh1pQgk0#v=onepage&q=brock%20microbiology%20biofilm&f=false e-Study Guide for Brock Biology of Microorganisms, textbook by Michael T. Madigan.]<groups/ref>. Examples of biofilms are dental plaque and the green film produced by algae that covers stones in water streams <ref name="montana">[http:MilkTheFunk/permalink/www.biofilm.montana.edu1524191477609061/node/2390 Center For Biofilm EngineeringPellicle formed by what is likely identified to be ''Pichia anomala''. Montona State University. Retrieved 09/05/2015Photo provided by Nick Rutkowski.]</ref>]] An often asked question by homebrewers is can a contaminating or wild caught microbe be identified based on the appearance of a pellicle. Biofilms are encountered in brewing in This is a difficult exercise for a few reasons. # There is very little research on pellicles when it comes to beer fermentation, so saying anything definitive about them is difficult, and identifying one or more microbes that created a pellicle based on what the form pellicle looks like is currently impossible.# The number and size of contaminating microorganisms and poor cleaning/sanitation techniques. Biofilms are bubbles in a common source of persistent brewhouse infections and can be resistant to pellicle is largely dependent on the actions amount of many cleaning trapped CO2, and sanitizing agents <ref name="montana"></ref><ref name="Bryan">Private conversation with Drthus is not an identifying feature. Bryan Heit.</ref># The factors that cause pellicle formation are not well understood. Pellicles Oxygen is said to cause pellicle formation, but how, why, and in beer do what species is not attach to known. Does more oxygen create a solid surfacethicker pellicle? If so, they appear on the "air-liquid interface" for what species does this apply to? Does beer composition (the surface of the beermore or less protein content, residual sugars, etc.). affect pellicle appearance? They The lack of answers to these questions and others imply that environmental factors are also not colonies within an adhesive <ref name="Bryan">helpful in identifying what species of microbe produced a pellicle.# Identification of microbe species and sometimes even genus under a [[Microscope|microscope]] based on cell morphology alone is not enough to be certain of that identification (see [httpshttp://wwwsuigenerisbrewing.facebookblogspot.com/groups2014/MilkTheFunk12/permalink/1131334646894748/?comment_id=1131986723496207&offset=0&total_comments=57&comment_tracking=%7B%22tn%22%3A%22R3%22%7D Conversation with Bryan Heit about Pellicles brett-trois-riddle-wrapped-in-mystery.html this article on MTF. 08/20/2015.Trois identification] </ref>. To make matters even more confusingas an example), the two established definitions of let alone attempting to identify microbes based on a visual "pelliclemacro-level" in biology are the outer boundary of formation such as a protozoa cell <ref>[https://bookspellicle.google.com/books?id=ACBcDjDLuNAC&pg=PA38&lpg=PA38&dq=pellicle+biology&source=bl&ots=58e43A_9h-&sig=ViakT4Ectu4DOlqoSWRCPFJ73iw&hl=en&sa=X&sqi=2&ved=0CGIQ6AEwDGoVChMIp6WkouTAxwIVgpmICh0F1wXO #v=onepage&q=pellicle%20biology&f=false Biology DNA analysis of Protozoa. D.R. Khanna. Discovery Publishing House, Jan 1, 2004. Pg 38.]</ref>, and a microbe is the protein film that forms on only way to reliably identify the surface species of teeth <ref>a microbe. This is why [httpshttp://enbootlegbiology.wikipedia.orgcom/2015/wiki09/Dental_pellicle Wikipedia. Dental Pellicle. Retrieved 0817/23local-yeast-project-study-barrel-culture-t-shirts/2015.Bootleg Biology is launching a program to identify wild caught microbes through DNA analysis]</ref>.

The usage of the term "biofilm" has been used above stated, it might be possible to make an educated guess as to describe the layer genus of film a microbe that covers sherry known as "Flor" <ref>[http://aem.asm.org/content/76/12/4089.full Ethanol-Independent Biofilm Formation by produced a pellicle if there was a Flor Wine Yeast Strain of Saccharomyces cerevisiae. Severino Zaracontrolled study (same wort, Michael K. Gross, Giacomo Zarasame incubation conditions, Marilena Budroni and Alan Tetc. Bakalinsky. 2010.]</ref><ref>[http://femsle.oxfordjournals.org/content/femsle/237/2/425.full.pdf FLO11 is essential for flor formation caused ) that examined the visual differences between pellicles formed by the C-terminal deletion different genera of NRG1 in Saccharomyces cerevisiaemicrobes. Mari IshigamiUnfortunately, Youji Nakagawa, Masayuki Hayakawa, Yuzuru Iimura. 2004.]</ref>such a study has not been performed that we know of. The word "pellicle" generally isn't usedTherefore, although it has appeared on occasion when referring to sherry flor in is currently unknown if the 1960's <ref>[http://www.ncbi.nlm.nih.gov/pubmed/5311988 On the pellicle formation by “flor” yeasts. Cantarelli C, Martini A. Antonie Van Leeuwenhoek. 1969.]</ref>. More recently, there have been studies that define genus of a "pellicle" like we see in fermentation as a type of biofilm that forms contaminating microbe can be determined based on the air-liquid interface visual appearance of a liquid (see references) <ref name="Armitano"></ref><ref>[http://www.ncbi.nlm.nih.gov/pubmed/26122431 Motilitythe pellicle alone, Chemotaxis and Aerotaxis Contribute to Competitiveness during Bacterial Pellicle Biofilm Development. Hölscher T, Bartels B, Lin YC, Gallegos-Monterrosa R, Price-Whelan A, Kolter R, Dietrich LE, Kovács ÁT. J Mol Biol. 2015 Jun 26.]</ref>though it is probably unlikely <ref>[httphttps://www.ncbifacebook.nlm.nih.govcom/pubmedgroups/24035282 Modulation of curli assembly and pellicle biofilm formation by chemical and protein chaperones. Andersson EK, Bengtsson C, Evans ML, Chorell E, Sellstedt M, Lindgren AE, Hufnagel DA, Bhattacharya M, Tessier PM, Wittung-Stafshede P, Almqvist F, Chapman MR. Chem Biol. 2013 Oct 24.]<MilkTheFunk/ref><ref>[http:permalink/1153845284643684/www.horadent.com/uploads/media/2005_Branda.pdf Biofilms: the matrix revisited. Steven S. Branda, Ashild Vik, Lisa Friedman ?comment_id=1153891934639019&reply_comment_id=1154095574618655&total_comments=5&comment_tracking=%7B%22tn%22%3A%22R2%22%7D Conversation with Richard Preiss and Roberto Kolterothers on MTF. Jan 2005.]<09/ref><ref>[http:24//onlinelibrary.wiley.com/doi/10.1046/j.1365-2958.2003.03877.x/full Genes involved in matrix formation in Pseudomonas aeruginosa PA14 biofilms. Lisa Friedman andRoberto Kolter. Dec 20032015.]</ref>. However, according to Dr. Bryan Heit, the use (or misuse) of the term "biofilm" in these few studies does not warrant a change in the already established definition of the scientific term "biofilm" <ref name="Bryan"></ref>.

The importance of understanding this terminology becomes apparent when trying to research the topic of * See also [[Wild_Yeast_Isolation#Growing_and_Testing_Without_Plating|Wild Yeast isolation]] for more information on wild yeast isolation, pellicles in beer. Currently they have not been studied much at all, whereas pellicles of dentistry and microbiology have been studied in depth, as well as biofilms. Thus, brewers should take care when researching scientific publicationssafety.

Most Many brewers will advise that if it all possible, try not to disturb the pellicle too much when taking a sample, racking, or moving the fermenting fermentation vessel. However, if the pellicle is disturbed, this should be fine as long as the beer is not exposed to too much oxygen. If taking a sample or racking, gently pierce the top of the pellicle with the racking cane or wine thief. If the pellicle does break up, don't worry too much. It will usually reform if oxygen is still present in the headspace. Purging with CO2 might be a good idea if you think that a lot of oxygen got introduced during handling. While packaging the beer, try not to disturb the pellicle too much because clumps of the pellicle on the surface of the beer can fall back into solution when disturbed, and can then get transferred into the bottles or kegs. If the beer is being transferred, if fruits are being added, if new product is being added in a [[Solera]] process, or if it is being used as a starter for another batch, do not worry about disturbing the pellicle. Disturbing the pellicle isn't really a problem; letting in too much oxygen is the problem.

Often a pellicle will form on the surface of the beer inside the bottle shortly after packaging. This is no different than the pellicle forming in the fermentation vessel, and presumably occurs because of the oxygen in the headspace of the bottle. The pellicle will eventually settle out either on it's its own during aging, or when the bottle is refrigeratedor disturbed. Other than for aesthetics, there should be no concern if this happens. Pierre Tilquin of [http://www.gueuzerietilquin.be Gueuzerie Tilquin] suggests that storing bottles horizontally on their side during bottle conditioning will prevent a pellicle from forming in the bottles. This is a common practice among lambic brewers, and when Pierre stored bottles upright he saw the formation of a pellicle in his bottles of lambic <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1210209235673955/?comment_id=1210248462336699&reply_comment_id=1210254505669428&comment_tracking=%7B%22tn%22%3A%22R8%22%7D Conversation with Pierre Tilquin and Raf Soef on MTF. 01/08/2016.]</ref>. Gently tipping the bottles or even just standard handling will also dissolve the pellicle without harming the beer. See also [[Aging_and_Storage#Bottle_Orientation|Bottle Orientation]]. ==Scientific Terminology==As with some things in science that are not greatly explored, terminology isn't always agreed upon or fully established, and thus researching such a topic without a lot of prior knowledge can be challenging. Pellicles are a good example of this.  It is sometimes stated that a pellicle is a type of biofilm. However, there have been objections made to defining a pellicle as a type of biofilm. [http://www.biofilm.montana.edu/node/2390 Biofilms] are well studied and understood in science. Many microbiology textbooks define a biofilm as an aggregate of microorganisms where the cells adhere to each other on a solid surface <ref>[https://books.google.com/books?id=-ZDKAQAAQBAJ&pg=PT87&lpg=PT87&dq=brock+microbiology+biofilm&source=bl&ots=PwNZ20KFqq&sig=19lvlfqYj8bE7roiA7g4oJ3Xl0E&hl=en&sa=X&ved=0CCcQ6AEwAWoVChMImZaUmN_AxwIVVFmICh1pQgk0#v=onepage&q=brock%20microbiology%20biofilm&f=false e-Study Guide for Brock Biology of Microorganisms, textbook by Michael T. Madigan.]</ref>. Pellicles do not adhere to a solid surface, and are said to form at the "air-liquid interface" (surface of beer). As such they do not fit the definition of a biofilm in the strictest sense. However, the IUPAC, which is an international federation of National Adhering Organizations that works to standardize nomenclature in chemistry and other fields of science, defines a biofilm as an "aggregate of microorganisms in which cells that are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS) adhere to each other and/or to a surface <ref>[http://www.degruyter.com/view/j/pac.2012.84.issue-2/pac-rec-10-12-04/pac-rec-10-12-04.xml Pure and Applied Chemistry. Volume 84, Issue 2, Pages 377–410, ISSN (Online) 1365-3075, ISSN (Print) 0033-4545, DOI: 10.1351/PAC-REC-10-12-04, January 2012.]</ref>." According to the IUPAC, the "and/or" part of the definition allows for pellicles to be defined as biofilms since the cells adhere to each other.  Biofilms are extremely diverse and abundant in nature. Examples of biofilms in the classical sense include dental plaque and the green film produced by algae that covers stones in water streams <ref name="montana">[http://www.biofilm.montana.edu/node/2390 Center For Biofilm Engineering. Montona State University. Retrieved 09/05/2015.]</ref>. Biofilms are encountered in brewing in the form of contaminating microorganisms and poor cleaning/sanitation techniques. Biofilms are a common source of persistent brewhouse infections and can be resistant to the actions of many cleaning and sanitizing agents <ref name="montana"></ref><ref name="MTF_Thread"></ref>. Pellicles in beer do not attach to a solid surface, they appear on the "air-liquid interface" (the surface of the beer) <ref name="MTF_Thread">[https://www.facebook.com/groups/MilkTheFunk/permalink/1131334646894748/?comment_id=1131986723496207&offset=0&total_comments=57&comment_tracking=%7B%22tn%22%3A%22R3%22%7D Conversation about Pellicles on MTF. 08/20/2015.] </ref>. To make matters even more confusing, the two established definitions of a "pellicle" in biology only include the outer boundary of a protozoa cell <ref>[https://books.google.com/books?id=ACBcDjDLuNAC&pg=PA38&lpg=PA38&dq=pellicle+biology&source=bl&ots=58e43A_9h-&sig=ViakT4Ectu4DOlqoSWRCPFJ73iw&hl=en&sa=X&sqi=2&ved=0CGIQ6AEwDGoVChMIp6WkouTAxwIVgpmICh0F1wXO#v=onepage&q=pellicle%20biology&f=false Biology of Protozoa. D.R. Khanna. Discovery Publishing House, Jan 1, 2004. Pg 38.]</ref>, and the protein film that forms on the surface of teeth <ref>[https://en.wikipedia.org/wiki/Dental_pellicle Wikipedia. Dental Pellicle. Retrieved 08/23/2015.]</ref>. The usage of the term "biofilm" has been used to describe the layer of film that covers sherry known as "Flor" <ref>[http://aem.asm.org/content/76/12/4089.full Ethanol-Independent Biofilm Formation by a Flor Wine Yeast Strain of Saccharomyces cerevisiae. Severino Zara, Michael K. Gross, Giacomo Zara, Marilena Budroni and Alan T. Bakalinsky. 2010.]</ref><ref>[http://femsle.oxfordjournals.org/content/femsle/237/2/425.full.pdf FLO11 is essential for flor formation caused by the C-terminal deletion of NRG1 in Saccharomyces cerevisiae. Mari Ishigami, Youji Nakagawa, Masayuki Hayakawa, Yuzuru Iimura. 2004.]</ref>. The word "pellicle" generally isn't used, although it has appeared on occasion when referring to sherry flor in the 1960's <ref>[http://www.ncbi.nlm.nih.gov/pubmed/5311988 On the pellicle formation by “flor” yeasts. Cantarelli C, Martini A. Antonie Van Leeuwenhoek. 1969.]</ref>, and as least once in brewing science from the 1960's <ref name="Macrae_1964">[https://onlinelibrary.wiley.com/doi/abs/10.1002/j.2050-0416.1964.tb02001.x SIGNIFICANCE OF THE USE OF HOPS IN REGARD TO THE BIOLOGICAL STABILITY OF BEER: I. REVIEW AND PRELIMINARY STUDIES. R. M. Macrae. 1964.]</ref>. More recently, there have been studies that define a "pellicle" like we see in fermentation as a type of biofilm that forms on the air-liquid interface of a liquid (see references: <ref name="Armitano"></ref><ref>[http://www.ncbi.nlm.nih.gov/pubmed/26122431 Motility, Chemotaxis and Aerotaxis Contribute to Competitiveness during Bacterial Pellicle Biofilm Development. Hölscher T, Bartels B, Lin YC, Gallegos-Monterrosa R, Price-Whelan A, Kolter R, Dietrich LE, Kovács ÁT. J Mol Biol. 2015 Jun 26.]</ref><ref>[http://www.ncbi.nlm.nih.gov/pubmed/24035282 Modulation of curli assembly and pellicle biofilm formation by chemical and protein chaperones. Andersson EK, Bengtsson C, Evans ML, Chorell E, Sellstedt M, Lindgren AE, Hufnagel DA, Bhattacharya M, Tessier PM, Wittung-Stafshede P, Almqvist F, Chapman MR. Chem Biol. 2013 Oct 24.]</ref><ref name="Branda">[http://www.horadent.com/uploads/media/2005_Branda.pdf Biofilms: the matrix revisited. Steven S. Branda, Ashild Vik, Lisa Friedman and Roberto Kolter. Jan 2005.]</ref><ref>[http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2958.2003.03877.x/full Genes involved in matrix formation in Pseudomonas aeruginosa PA14 biofilms. Lisa Friedman andRoberto Kolter. Dec 2003.]</ref><ref>[http://aem.asm.org/content/77/15/5079.short Increased Transfer of a Multidrug Resistance Plasmid in Escherichia coli Biofilms at the Air-Liquid Interface. Jaroslaw E. Król, Hung Duc Nguyen, Linda M. Rogers, Haluk Beyenal, Stephen M. Krone1, and Eva M. Top. 2011.]</ref><ref>[https://books.google.com/books?id=PO3QrZJnuGgC&pg=PA7&dq=biofilm+air-liquid+interface&hl=en&sa=X&ved=0CDAQ6AEwBGoVChMIjP--39D5xwIVFDWICh285gg_#v=onepage&q=biofilm%20air-liquid%20interface&f=false Bacterial Biofilms. Tony Romeo. Springer Science & Business Media, Feb 26, 2008. Pg 7.]</ref>). Lebleux et al. (2019) defines biofilm as, "Biofilms are complex associations of single- and multiple- species interconnected cells embedded in a hydrated self-produced matrix established at a solid/liquid or liquid/air interfaces." <ref>[https://www.sciencedirect.com/science/article/abs/pii/S0168160519303952 New advances on the Brettanomyces bruxellensis biofilm mode of life. Manon Lebleux, Hany Abdo, Christian Coelho, Louise Basmaciyan, Warren Albertin, Julie Maupeu, Julie Laurent, Chloé Roullier-Gall, Hervé Alexandre, Michèle Guilloux-Benatier, Stéphanie Weidmann, Sandrine Rousseaux. 2019. DOI: https://doi.org/10.1016/j.ijfoodmicro.2019.108464.]</ref> However, those objecting to the definition of a biofilm as including air-liquid interface aggregates say that the use of the term in a few studies does not warrant a change in the textbook definition <ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/1142388839122662/ Discussion of this wikipage on MTF. 09/06/2015.]</ref>.  The importance of understanding the established terminology of "biofilms" and "pellicles" versus the brewing terminology becomes apparent when trying to research the topic of pellicles in beer. Currently beer pellicles have not been studied scientifically much at all, whereas pellicles of dentistry and microbiology have been studied in depth, as well as biofilms in general. Thus, brewers should take care when reading scientific publications, and understand that brewing terminology does not usually overlap with scientific terminology in regards to pellicles. See also:* [[Quality_Assurance#Biofilms|Biofilms]]