Why does my coffee taste burnt?

There are three different unpleasant tastes people describe as burnt: genuine burnt from heat applied after brewing, bitterness from over-extraction, and the ashy character of very dark-roasted beans. Each has a different remedy.

What you'll need

• Your coffee equipment
• Thermometer (optional)

Step by step

1. Check whether the coffee has been sitting on a hot plate.This is the most common cause. Coffee held on a warming plate develops a burnt, stewed flavour within twenty minutes. Brew into a thermal flask instead.
2. Check your water temperature.Above about 96°C scalds the grounds and produces harsh burnt notes. Let a kettle stand for thirty seconds after boiling.
3. Look at the beans themselves.Very dark, oily beans with a shiny surface are roasted to the point where roast character dominates. That is inherent, not a brewing fault.
4. Check the machine is clean.Rancid coffee oils in a machine, grinder or filter basket taste acrid and transfer to every cup. This is very commonly the answer.
5. Check the grind is not too fine for the method.Too fine means over-extraction, which reads as bitterness rather than true burning but is often described the same way.
6. Reduce the brew time if it is over-extracting.Cafetière over five minutes, or espresso running long, both pull harsh compounds out at the end of extraction.
7. Descale if you are in a hard water area.Scale on a heating element causes local overheating and gives a burnt character to the water itself.
8. Try a lighter roast.If everything else is right and it still tastes of ash, the roast is the answer. Medium roasts show origin flavour rather than roast flavour.

Tips

• Never microwave coffee to reheat it. It heats unevenly, drives off aromatics and reliably produces a burnt taste.
• Clean the grinder as well as the machine. Old grounds in a burr grinder go rancid and taint everything after them.
• Buy smaller quantities more often. Stale beans plus a dark roast is the most common burnt-tasting combination.

Common mistakes

• Keeping coffee warm on a hot plate — It continues cooking, and the burnt stewed flavour develops within about twenty minutes. A thermal flask holds it for hours with no change.
• Pouring water straight off the boil — It scalds the grounds. Thirty seconds off the boil brings it into the right range.
• Never cleaning the equipment — Rancid coffee oils build up on every surface and taste acrid. It is the most-missed cause by a wide margin.

Questions people ask