Symptoms
- Coffee tastes bitter, sour, or plasticky
- Coffee smells musty or stale
- Taste changed recently with no change in beans
- Water left in reservoir between uses
Likely causes
- CommonMineral scale buildup affecting water qualityScale can impart a metallic or bitter taste as it breaks down during brewing.
- CommonOld coffee oil residue in the carafe or basketOils go rancid and coat surfaces, tainting every new pot.
- CommonStale water sitting in the reservoir between brewsStanding water picks up plastic and mineral off-flavors.
- PossibleMold or mildew inside the reservoir or tubingDamp, dark internal spaces are prone to buildup if not cleaned regularly.
- PossibleOld or stale coffee groundsThis is a coffee freshness issue rather than a machine issue, but easy to rule out.
What to do
- Empty and rinse the reservoir before every use rather than leaving water sitting overnight.
- Wash the removable carafe, basket, and lid with warm soapy water and a soft brush, rinsing thoroughly.
- Run a descaling cycle with a 50/50 vinegar-water mix through a full brew, then two cycles of plain water.
- Check reservoir and tubing for visible mold or dark residue; clean or descale again if present.
- Try a fresh bag of coffee to rule out stale beans or grounds.
- If taste is still off after descaling and cleaning, mineral deposits deep in the tubing may need a repeat descale or the machine may be near end of life.
Tools and parts
- Soft bottle brush
Coffee maker descaling solutionSearch: “coffee maker descaler”
When to call a pro
This is a DIY cleaning issue; a professional isn't needed unless the taste persists after thorough cleaning, at which point replacing the machine is more practical.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.