Editing Pellicle
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[[File:Cider-pellicle-resized.jpg|thumb|right| | [[Category:Fermentation products]] | ||
A pellicle is a film | [[File:Cider-pellicle-resized.jpg|thumb|right|The pellicle on a cider pitched with wild microbes, courtesy of Dr. Adam Bittner]] | ||
A pellicle is a film that can form on the surface of a fermentation. It is created by some types of yeast and bacteria, when oxygen is present.<ref name="MTF-pellicle">[http://www.milkthefunk.com/wiki/Pellicle "Pellicle"] Milk the Funk wiki. Accessed April 2020.</ref> A pellicle may be white, off-white, or clear and it generally has a powdery, waxy, or slimy appearance, often with bubbles or wrinkles (never fuzzy or hairy). It should not be confused with [[mold]], [[kraüsen]], "[[yeast rafts]]", or films from oils. | |||
Pellicles can be formed by a variety of wild yeast and bacteria.<ref name="MTF-pellicle"/> Therefore it is not possible to identify which microbes(s) may be present based solely on the appearance of the pellicle or its characteristics — microbiological testing must be performed for identification.<ref>Widmayer | Pellicles can be formed by a variety of wild yeast and bacteria.<ref name="MTF-pellicle"/> Therefore it is not possible to identify which microbes(s) may be present based solely on the appearance of the pellicle or its characteristics — microbiological testing must be performed for identification.<ref>Widmayer, Cory. [https://www.facebook.com/groups/MilkTheFunk/permalink/3292440674117457/ Thread with comments from a fermentation/yeast researcher.] Milk the Funk Facebook group. Feb 2020.</ref> | ||
Since commercial strains of [[brewers yeast]] used for [[beer]] and [[wine]] do not form a pellicle (except for [[sherry]]/flor yeast<ref>Eldarov MA, | Since commercial strains of [[brewers yeast]] used for [[beer]] and [[wine]] do not form a pellicle (except for [[sherry]]/flor yeast<ref>Eldarov MA, et al. [https://www.frontiersin.org/articles/10.3389/fmicb.2018.00965/full "Whole-Genome Analysis of Three Yeast Strains Used for Production of Sherry-Like Wines Revealed Genetic Traits Specific to Flor Yeasts."] ''Front. Microbiol.'', vol. 9, no. 965, 2018.</ref><ref>Van Mulders, S.E., et al. [https://lirias.kuleuven.be/retrieve/129510 "Flocculation gene variability in industrial brewer’s yeast strains."] ''Appl Microbiol Biotechnol'', vol. 88, 2010, pp. 1321–1331.</ref> and possibly WLP644<ref>[https://www.whitelabs.com/sites/default/files/644_Explanation.pdf "644 Explanation."] White Labs. Accessed online April 2020.</ref>), it can be an indisputable sign of contamination.<ref name="Humbard"/> (See [[Contamination]] for more info.) | ||
On the other hand, pellicle formation is normal for fermentations that contain wild microbes or non- | On the other hand, pellicle formation is normal for fermentations that contain wild microbes or non-Saccharomyces cultures such as [[Brettanomyces]].<ref>[https://www.homebrewtalk.com/forum/threads/pellicle-photo-collection.174033/ "Pellicle Photo Collection."] Forum thread. HomeBrewTalk. 2010.</ref> For example, a pellicle frequently forms in [[sour beer|mixed-fermentation beers]] or wines/ciders/meads with Brettanomyces or unpasteurized fruit or honey, and pellicle formation is a hallmark of [[kombucha]] and [[vinegar]] production. The appearance of a pellicle in these products doesn't reflect what may be happening in the fermentation with regard to quality or progress, it merely indicates the presence of the microbes.<ref name="Humbard"/> In wine, adequate pH-adjusted [[sulfite]] levels post-fermentation can inhibit these microbes and therefore prevent the formation of a pellicle. | ||
"Kahm yeast" is a colloquial term for a pellicle,<ref>Colleen. [https://fermentools.com/what-is-kahm-yeast-is-it-safe/ What is | "Kahm yeast" is a colloquial term for a pellicle,<ref>Colleen. [https://fermentools.com/what-is-kahm-yeast-is-it-safe/ "What is Kahm Yeast & is it Safe?"] Fermentools. September 2018.</ref> and it is a misnomer because it is not always created by yeast. Similarly, the pellicle on [[kombucha]] is often mistakenly called the "SCOBY". | ||
== Pellicle test == | ===Pellicle test=== | ||
If you aren't sure whether an unknown film is a pellicle, you can do what we call a "Forced Pellicle Test", and it's easy: | If you aren't sure whether an unknown film is a pellicle, you can do what we call a "Forced Pellicle Test", and it's easy: | ||
# Add a small sample of the liquid into a sanitized jar or other container. | # Add a small sample of the liquid into a sanitized jar or other container. | ||
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If you still aren't sure, leave it undisturbed for several more days and check again. Any fuzzy or hairy growth is [[mold]]. | If you still aren't sure, leave it undisturbed for several more days and check again. Any fuzzy or hairy growth is [[mold]]. | ||
This test is based on the fact that oxygen exposure generally stimulates pellicle formation.<ref name="MTF-pellicle"/><ref name="Humbard">Humbard | This test is based on the fact that oxygen exposure generally stimulates pellicle formation.<ref name="MTF-pellicle"/><ref name="Humbard">Humbard, Matt. [https://phdinbeer.com/2015/01/30/beer-microbiology-what-is-a-pellicle/ "Beer Microbiology – What is a pellicle?"] A Ph.D. in Beer – A Study of Beer and Fermentation Science. Jan 2015.</ref><ref>Nakagawa, Y., et al. [https://www.tandfonline.com/doi/full/10.1080/13102818.2016.1246203 "Glucose repression of FLO11 gene expression regulates pellicle formation by a wild pellicle-forming yeast strain isolated from contaminated wine."] ''Biotechnology & Biotechnological Equipment,'' vol. 31, no. 1, 2017, pp. 120–127.</ref> | ||
== Myths == | ==Myths== | ||
Myth: '''Brewers yeast can form a pellicle.'''<br /> | |||
Truth: With the exception of sherry (flor) yeast, it does not. This myth stems from brewers with recurrent [[contamination]] issues.<ref>[https://www.homebrewtalk.com/forum/threads/thin-white-film-floating-in-secondary.49591/ "Thin white film floating in secondary?"] Forum thread. HomeBrewTalk. December 2007.</ref><ref>[https://www.homebrewtalk.com/forum/threads/post-your-infection.71400/page-98#post-8835819 "Post your infection."] Forum thread. HomeBrewTalk. April 2020.</ref> In reality, unless you pitch a yeast known to form a pellicle, any pellicle was definitely created by wild microbes that were somehow introduced into the beer or wine. | |||
We have reached out to some of the major yeast labs to verify whether their strains produce pellicles: | We have reached out to some of the major yeast labs to verify whether their strains produce pellicles: | ||
* Wyeast: "Wyeast Laboratories, Inc. does not have any commercial | * Wyeast:<ref>Logsdon, Tamara (Wyeast QC Lab Coordinator and Brand Manager). "Pellicle formation." Personal email correspondence received by Adam Bittner. April 22, 2020.</ref> "Wyeast Laboratories, Inc. does not have any commercial Saccharomyces strains that form pellicles." | ||
* Fermentis:<ref>Pizarro, José (Fermentis Regional Sales Manager for North America – East & Gulf of Mexico). "FW: Other request from Fermentis Website." Personal email correspondence received by Adam Bittner. April 22, 2020.</ref> "None of our strains (Fermentis or Red Star) have that ability [to form a pellicle] in any circumstances." | |||
* White Labs:<ref>Taylor, Kara (Head of Laboratory Operations at White Labs). "Pellicle Formation." Personal email correspondence received by Adam Bittner. April 23, 2020.</ref> "Pellicle formation isn't common with our Saccharomyces strains. We have seen it with [https://www.whitelabs.com/yeast-bank/wlp644-saccharomyces-bruxellensis-trois WLP644] and [https://www.whitelabs.com/yeast-bank/wlp700-flor-sherry-yeast WLP700] but that's likely it." | |||
* Omega:<ref>Shaner, Lance (Owner of Omega Yeast Labs). "Pellicle formation." Personal email correspondence received by Adam Bittner. April 24, 2020.</ref> "I am not aware of any of our Sacch strains being able to form a pellicle. We have a handful of "wild" Sacch strains and haven't seen it with them either." | |||
* GigaYeast:<ref>Withee, Jim (President of GigaYeast). "Pellicle formation." Personal email correspondence received by Adam Bittner. April 24, 2020.</ref> "We bank and grow hundreds of yeast strains and have never encountered a domesticated brewers yeast strain that exhibited pellicle formation." | |||
* Imperial:<ref>Caudill, Jess (Imperial Yeast representative). "Pellicle formation." Personal email correspondence received by Adam Bittner. April 27, 2020.</ref> "We have not run trials on pellicle formation with Saccharomyces strains specifically as this usually isn't a consideration when using them in the short duration fermentation process." | |||
* Lallemand:<ref>Shayevitz, Avi (Lallemand R&D Associate). "Pellicle formation." Personal email correspondence received by Adam Bittner. April 28, 2020.</ref> "None of the Saccharomyces cerevisiae strains available through Lallemand for brewing or wine production are known to produce pellicles under tested laboratory conditions. No pellicle formation observations have been made in the presence of pure cultures." | |||
* Escarpment:<ref>Preiss, Richard (Escarpment Labs R&D associate and one of the founders). "Pellicle formation." Personal email correspondence received by Adam Bittner. April 30, 2020.</ref> "None of our Saccharomyces strains are capable of forming pellicles/films. Among Saccharomyces this seems to be fairly limited to sherry flor yeasts, which have some modifications in flocculation genes that seems to help them form rafts/films. " | |||
On his [https://phdinbeer.com/2015/01/30/beer-microbiology-what-is-a-pellicle/ blog], Dr. Matt Humbard discusses the ability of | On his [https://phdinbeer.com/2015/01/30/beer-microbiology-what-is-a-pellicle/ blog], Dr. Matt Humbard discusses the ability of Saccharomyces to form a pellicle. | ||
Myth: '''White Labs WLP644 forms a pellicle.'''<br /> | |||
Truth: It is questionable whether [https://www.whitelabs.com/yeast-bank/wlp644-saccharomyces-bruxellensis-trois WLP644 Saccharomyces "Bruxellensis" Trois] can actually form a pellicle. When this culture was first released, it was noted to form a pellicle. However, there was a shift in quality control practices in 2017 with the Left Hand ''vs.'' White Labs lawsuit. Since then, there have been no validated reports of this strain forming a pellicle.<ref>[https://www.facebook.com/groups/MilkTheFunk/permalink/3465266216834901/ Thread about WLP644 Pellicle Formation.] Milk the Funk Facebook group. April 2020.</ref> Nevertheless, White Labs continues to claim that WLP644 can possibly form a pellicle, as noted above. | |||
Myth: '''You can rack from under a pellicle to remove the contamination.'''<br /> | |||
Truth: Contaminating microbes are present throughout the liquid. For example microbes like Brett, Lacto, and Pedio are able to be grown from bottles of mixed-fermentation beers 30+ years later, every though those were obviously not bottled with the pellicle from the barrels. | |||
Myth: '''All wild microbes (e.g. contaminants) form a pellicle.'''<br /> | |||
Truth: Not all wild mixed yeast/bacteria cultures form pellicles. This is easy to demonstrate by those of us repeatedly (and intentionally) capturing wild cultures. The genes that cause pellicle formation aren't always turned on, even if they are present.<ref>Bumgarner, SL., et al. [https://www.pnas.org/content/106/43/18321.long "Toggle involving cis-interfering noncoding RNAs controls variegated gene expression in yeast."] ''PNAS'', vol. 106, no. 43, October 2009, pp. 18321-18326.</ref> | |||
==See also== | |||
* See [http://www.milkthefunk.com/wiki/Pellicle Pellicle] at Milk the Funk for more detailed information about pellicles. | * See [http://www.milkthefunk.com/wiki/Pellicle Pellicle] at Milk the Funk for more detailed information about pellicles. | ||
* [https://www.homebrewtalk.com/forum/threads/pellicle-photo-collection.174033/ Pellicle photo collection] on HomeBrewTalk.com | * [https://www.homebrewtalk.com/forum/threads/pellicle-photo-collection.174033/ Pellicle photo collection] on HomeBrewTalk.com | ||
* See [[Contamination]] for more information about how to proceed when your fermentation has an unexpected pellicle. | |||
==References== | ==References== | ||