Pellicle
A pellicle is a film that can form on the surface of a fermentation. It is a type of biofilm created by certain microbes in the presence of oxygen. A pellicle may be white, off-white, or clear and it generally has a powdery, waxy, or slimy appearance. It should not be confused with mold, kraüsen, or "yeast rafts".
A variety of wild microbes and some commercial cultures containing non-Saccharomyces are known to form a pellicle, and therefore it is not possible to identify the microbes(s) that may be present based on the appearance or other characteristics — unless microbiological testing is performed.
Since commercial strains of Saccharomyces do not form a pellicle (with one or two exceptions[1]), it is often a striking visual sign of contamination. However, in fermentations that contain wild microbes or non-Saccharomyces cultures such as Brettanomyces, the formation of a pellicle is a normal occurrence.
See also
See Contamination for more information about the effects of wild microbes and how to deal with them.
See Pellicle at Milk the Funk for more detailed information about pellicles.
Myths
Some home brewers attempting to make "clean" beers or wines regard pellicle formation as a "normal" occurrence. This is incorrect because it is only created by wild microbes.
- Statement from Wyeast:[2] "Wyeast Laboratories, Inc. does not have any commercial Saccharomyces strains that form pellicles."
- Statement from Fermentis:[3] "None of our strains (Fermentis or Red Star) have that ability [to form a pellicle] in any circumstances."
- Statement from White Labs:[4] "Pellicle formation isn't common with our Saccharomyces strains. We have seen it with WLP644 and WLP700 but that's likely it."
References
- ↑ "644 Explanation." White Labs. Accessed online April 2020.
- ↑ Logsdon, Tamara (Wyeast QC Lab Coordinator, Brand Manager). "Pellicle formation." Personal email correspondence received by Adam Bittner. April 22, 2020.
- ↑ Pizarro, José (Fermented 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.
- ↑ Taylor, Kara (White Labs Head of Laboratory Operations). "Pellicle Formation." Personal email correspondence received by Adam Bittner. April 23, 2020.