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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). They are also not colonies within an adhesive <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>. 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>), 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>.