A pellicle in brewing is a slimy, bubbly biofilm that forms on the surface of beer/mead/other fermented drinks, which can be a sign of an infection if not intentionally cultivated, especially in non-sour beers. While it can protect beer/mead from further oxidation, its presence usually indicates an undesirable microbial contamination from wild yeast or bacteria, permanently changing the flavor profile and necessitating either brewing with it on purpose or discarding the batch. Preventing infections requires rigorous sanitation of all brewing equipment.
What a pellicle is:
- A thin, slimy, gooey, or fuzzy layer that forms on the surface of a liquid.
- A type of biofilm made of a colony of microbes, proteins, and polymers.
- Often appears in the presence of oxygen, as microbes on the surface can access it for aerobic metabolism.
- Bubbles in a pellicle are often caused by carbon dioxide CO2 escaping from the beer.
Why it forms:
- Intentional brewing: In some sour beers/kombucha/mead, a pellicle is intentionally cultivated with specific wild yeasts and bacteria like Brettanomyces, Lactobacillus, or Pediococcus.
- Accidental infection: If not intentionally cultivated, it signals a contamination from wild microorganisms that have entered the beer after the boil, often during cooling or fermentation.
- Oxygen exposure: The formation of a pellicle can be triggered by oxygen entering the headspace of the fermenter, which allows aerobic bacteria to thrive on the surface.
How to handle an infected pellicle:
- Do not consume: Unless you are intentionally making a wild or sour beer, a pellicle usually means the beer's flavor will be permanently changed for the worse.
- Discard: The safest option for a contaminated batch is to discard it, unless you intentionally created the pellicle or have researched how to properly siphon your beverage from under the pellicle.
- Dedicate equipment: If you get an infection from wild yeast, you may need to dedicate some equipment to sour brewing or replace high-risk items like hydrometers and racking equipment.
How to prevent a pellicle infection:
- Maintain cleanliness: Thoroughly wash and disinfect all brewing equipment, especially fermenters, tubing, and any other items that come into contact with the wort after the boil.
- Replace equipment: Consider replacing equipment that may have been cross-contaminated, especially plastic fermenters, recommends MoreBeer.
- Ensure proper fermentation: Create the best possible working conditions for your brewer's yeast to outcompete any wild microbes.
See Also