Acetaldehyde (AA) too high
Cause
Excessive melt temperature or long residence time degrades PET, raising AA which taints water/CSD taste.
Corrective action
Lower barrel/melt temperature, reduce residence time, use AA-reducing additive, verify dryer dew point.
Diagnosis guide: Acetaldehyde (AA) above specification
What you will see
Residual acetaldehyde in the preform wall is above the level on the SKU spec sheet. Nothing shows on the preform itself: it surfaces as a sweet, fruity off-taste in still water, or as a failed taste panel or AA test after blowing.
Likely causes
- Melt temperature too high in the injection barrel or hot runner at the preform plant
- Long melt residence time (a small shot in a large barrel, or a stop-start run)
- High screw speed or back pressure adding shear heat to the melt
- A resin grade not specified for low-AA (still water) use
Do this first
Quarantine the lot and have preforms tested for AA before blowing more of it.
How to diagnose it
- Check the resin grade and any AA value on the lot Certificate of Analysis against the SKU spec sheet
- Have 5 preforms from the lot tested for residual AA by headspace gas chromatography
- Test a retained preform from a lot that passed taste testing alongside it
- Record the lot number and production date from the carton label
How to fix it
- Keep the lot quarantined until the AA result is known
- If AA is above specification, contact Delta with the test report and lot number for replacement under the quality guarantee