Quick Diagnosis
Common Causes
Coffee Oil Build Up
Coffee oils gradually coat the brew path and group head, becoming rancid over time. Coffee oils create bitter flavours that can transfer into every espresso.
Signs this is your problem:
- Bitter aftertaste
- Burnt flavours
- Dark residue around shower screen
- Flavour gets worse over time
How to Fix it:
- Backflush espresso machine weekly using cleaning tablets.
- Run cleaning cycles on bean-to-cup machine
Machine Needs Descaling
Limescale alters brewing temperature and water flow. Scale doesn't directly taste bitter, but it alters water temperature and extraction, which can produce a harsh, bitter espresso.
Signs this is your problem:
- Bitter coffee
- Slower Extraction
- Steam performance reduced
How to Fix it:
- Descale following your manaufacturer's instructions
Grind Too Fine
If your coffee is ground too finely, water passes through the coffee puck too slowly. This causes over-extraction, where excessive bitter compounds are dissolved from the coffee, resulting in a harsh or burnt flavour.
Signs this is your problem:
- Espresso pours very slowly or drips from the portafilter
- Shot takes longer than 30 seconds to extract
- Coffee tastes bitter or over-extracted
- Puck is very wet or difficult to knock out.
How to fix it:
- Adjust your grinder one step coarser and brew another espresso. Make only one adjustment at a time, allowing a few shots for the grinder to settle before making further changes. Aim for a balanced extraction of 25-30 seconds with a rich, even flow.
- If your espresso still tastes bitter after adjusting the grind, continue through the remaining troubleshooting steps, as poor machine maintenance or stale coffee beans may also be contributing to the problem.
Water Temperature Too High
Some espresso machines allow the brewing temperature to be adjusted. If the temperature is set too high, the coffee can become over-extracted, restuling in a bitter or burnt taste.
Signs this is your problem:
- Coffee tastes burnt rather than rich
- Bitterness started after changing machine settings
- Shots extract normally but flavour is harsh
How to Fix it:
If your machine has adjustable temperature settings, reduce the brew temperature by one step and test again. If the machine does not have temperature controls, ensure it is clean and free from limescale, as scale can affect temperature stability.
Old or Poor-Quality Coffee Beans
Coffee beans lose flavour as they age. Beans that are stale, poorly stored or over-roasted can produce a bitter, flat-tasting espresso even when your machine is working perfectly.
Signs this is your problem:
- Beans have been open for more than 3-4 weeks.
- Coffee lacks aroma before brewing
- Espresso tastes dull, bitter or lifeless
- The problem remains after cleaning the machine.
How to fix it:
- Use freshly roasted coffee beasn stored in an airtight container away from heat, moisture and direct sunlight. If you've recently cleaned and descaled your machine but the taste hasn't improve, trying a fresh bag of quality beans is often the quickest way to rule out the coffee itself.
Prevention
Quick Maintenance Checklist
Suitable Products
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Coffee Cleaner Tablets
Available Late 2026Removes coffee oils from the brewing system - for Bean to Cup machines
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