Openai/6939a858-8b8c-8006-b827-ae43c13df6f8

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gpt-5-1

User: You are an experienced brewmaster.

You are an experienced brewmaster. Can Lallemand Philly Sour yeast grow pellicle or is such a batch of beer contaminated?

Assistant: Short answer: Philly Sour does not form a pellicle.

Short answer: Philly Sour does not form a pellicle.

Lallemand Philly Sour (Lachancea thermotolerans) is a lactic-acid-producing yeast, but it behaves like a clean yeast in terms of surface growth. It does not create pellicles (no ropey film, bubbles trapped in a skin, or powdery white islands).

If you’re seeing a pellicle, it almost certainly means contamination, most commonly:

• Brettanomyces
• Pediococcus
• Lactobacillus (in mixed culture)
• Wild yeast + oxygen exposure

Key indicators it’s contamination:

• White/tan film with bubbles underneath
• Patchy islands or brain-like texture
• Development after active fermentation slows
• Funk, horsey, barnyard, or intense sour beyond expected Philly profile

Philly Sour alone gives:

• Clean lactic tartness (yogurt/lemon)
• No surface film
• No continued gravity drop months later

Conclusion: A pellicle ≠ Philly Sour. That batch is contaminated or unintentionally mixed-fermented. Whether it’s dump-worthy depends on aroma, flavor, and your tolerance for funk.

User: The aroma and taste are ok.

The aroma and taste are ok. The taste has a bit vinegar in it but the level is not terrible. However I am worried about keezer contamination

Assistant: You’re safe as long as it’s not Acetobacter + oxygen.

You’re safe as long as it’s not Acetobacter + oxygen.

Key points, no fluff:

• Vinegar note → likely low-level Acetobacter.
• Acetobacter is not airborne. It spreads via liquid contact, fruit flies, dirty lines, not by sharing headspace in a keezer.
• Cold + CO₂ pressure halts it.

Keezer risk assessment

• ✅ Same keezer, separate kegs → safe
• ✅ Serving through normal beer lines → safe
• ❌ Shared transfer hoses, racking canes, QDs without cleaning → risk
• ❌ Open fermenter near fruit flies → risk

What to do now

• Keep the keg cold and under pressure
• Do not open it repeatedly
• Clean/sanitize: - Liquid & gas QDs - Lines if this beer touched them
• No need to nuke the keezer or discard other kegs

If it’s carbed and sealed, it won’t contaminate anything else. Worst case: the beer slowly sharpens over time — not a system-wide infection.

User: It would be carbed and kept cold but the co2 lines are connected and shared between various kegs.

It would be carbed and kept cold but the co2 lines are connected and shared between various kegs.

Assistant: Still not a problem.

Still not a problem.

Why:

• CO₂ lines only see dry gas, not beer.
• Contaminants (Acetobacter, Brett, LAB) cannot travel upstream through gas posts under pressure.
• Check valves in regulators/manifolds add another barrier.

When it could be an issue (edge cases):

• Beer backed up into gas lines (overfilled keg + no check valve)
• Shared spunding line with liquid present
• Wild pressure swings causing liquid carryover

Quick sanity check

• Disconnect gas QD → if it’s dry and doesn’t smell sour, you’re fine.
• If paranoid: spray some starsan into the gas QD, reconnect.

Bottom line

• Shared CO₂ manifold = safe
• No keezer contamination risk
• Drink it sooner rather than later

If you want, describe the pellicle (thin skin vs chunky islands) and I can ID the likely culprit.

User: How like do I contaminate the kegs for later?

How like do I contaminate the kegs for later? I use sodium percarbonate to sanitize it.

Assistant: Low risk — but one correction first.

Low risk — but one correction first.

Sodium percarbonate is a cleaner, not a sanitizer. It removes organics very well, but it does not reliably kill Brett/LAB/Acetobacter on its own.

Actual contamination risk

• Kegs used for that beer: low
• Future beers infected if cleaned properly: very unlikely
• Biggest risk parts: dip tubes, posts, poppets, O-rings

Best-practice reset (fast + effective)

1. Percarbonate soak (hot) - Disassemble keg completely - 30–60 min soak
2. Rinse thoroughly
3. Acid sanitizer (mandatory) - Star San / PAA / iodophor - Reassemble wet with sanitizer
4. Optional but solid: - Replace O-rings (cheap insurance)

What not to worry about

• Stainless steel: non-porous
• CO₂ exposure
• Cold storage

Bottom line

• Percarbonate alone = not enough
• Percarbonate + proper sanitizer = near zero risk
• No need to dedicate kegs unless you intentionally brew mixed ferms

If you want absolute certainty: boil dip tubes for 10 min and replace O-rings once.