Pellicle
Contents
Introduction
Pellicles form when the surface of the beer is exposed to oxygen [2] One theory is that the formation of a pellicle allows the organism to access the small amount of oxygen that is present in the headspace of the fermentation vessel. Another theory, and one that may be less accurate according to Dr. Matt Humbard, is that the pellicle protects the beer from other microorganisms [1]. 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.
Note About the Science and Terminology
(This section in progress)
As with some things in science that are not greatly explored, terminology isn't always agreed upon or fully established. Pellicles are a good example of this. It's been stated on this wiki and elsewhere that a pellicle is a subtype of biofilm. However, the widely accepted definition of a "biofilm" in biology doesn't describe pellicles that we see in fermentation. The widely accepted definition of a "biofilm" is an aggregate of microorganisms where the cells adhere to each other on a surface [3]. 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 [4]. To make matters even more confusing, the two widely accepted definitions of a "pellicle" in biology are the outer boundary of a protozoa cell [5], and the protein film that forms on the surface of teeth [6].
Recently, there have been studies that define a "pellicle" as we see in fermentation as a type of biofilm that forms on the air-liquid interface of a liquid (see references) [7][8][9][10]. Although these studies don't directly look at beer pellicles, this indicates that the definition of a pellicle as stated in this wiki may become more widely accepted in the scientific community.
The bottom line is that what is referred to as a "pellicle" in fermentation has not been widely studied, and the terminology is not widely established yet scientifically. Indeed, when researching "biofilms" and "pellicles", results will mostly refer to the more well established topics. Research done on traditional biofilms cannot necessarily be extrapolated to the pellicle phenomenon seen in fermentation.
Images
- See Google search images.
External Resources
References
- ↑ 1.0 1.1 Beer Microbiology – What is a pellicle? A PhD in Beer blog. Dr. Matt Humbard. 01/30/2015. Retrieved 04/26/2015.
- ↑ Brewing Sour Beer at Home. The Mad Fermentationist Blog. Michael Tonsmeire. 11/06/2009. Retrieved 02/28/2015.
- ↑ e-Study Guide for Brock Biology of Microorganisms, textbook by Michael T. Madigan.
- ↑ Conversation with Bryan Heit about Pellicles on MTF. 08/20/2015.
- ↑ Biology of Protozoa. D.R. Khanna. Discovery Publishing House, Jan 1, 2004. Pg 38.
- ↑ Wikipedia. Dental Pellicle. Retrieved 08/23/2015.
- ↑ Gram-negative bacteria can also form pellicles. Armitano J, Méjean V, Jourlin-Castelli C. Environ Microbiol Rep. 2014 Dec.
- ↑ Identification of genes essential for pellicle formation in Acinetobacter baumannii. Giles SK, Stroeher UH, Eijkelkamp BA, Brown MH. BMC Microbiol. 2015 Jun 6.
- ↑ 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.
- ↑ 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.