All symptoms
Diagnosis
OFF-FLAVOR / SOUR
Beer tastes buttery, vinegary, musty, or like wet cardboard.
3
LIKELY CAUSES — RANKED MOST COMMON FIRST
- 1
DIRTY DRAUGHT LINES
Biofilm and yeast in lines create diacetyl (butter), acetic (vinegar), or moldy notes.
Fix- Clean lines with caustic every 2 weeks, acid every 3 months.
- Recirculate cleaner ≥ 15 min at 1.5–2 gpm.
- Replace lines every 12–24 months depending on volume.
- 2
OXIDIZED BEER
Cardboard / sherry notes from O₂ ingress.
Fix- Never use air compressor as a pressure source.
- Check for cracked jumpers, loose keg couplers.
- 3
DIRTY GLASSWARE
Detergent or grease residue kills head and adds soapy taste.
Fix- Use a 3-sink wash with low-foam beer-glass detergent.
- Air-dry inverted on a deep-grooved rack — never towel-dry.
STILL NOT FIXED?
Capture temp at the faucet, applied PSI at the regulator, and a photo of the pour. Then check the spec reference or run a full line cleaning.