How do I descale a coffee machine?

Removing limescale from a coffee machine's water path, how often it needs doing, and why it is different from cleaning.

Difficulty: beginner
Time: 1 hr
Read: 2 min

Short answer

Run a descaling solution or citric acid through the machine following its own instructions, then rinse with two or three full tanks of fresh water. Descaling clears the water path; it does nothing to coffee oils, which need separate cleaning.

Scale builds up inside the boiler and pipework wherever hard water is heated. It slows flow, affects brewing temperature and eventually causes failure. It is a completely different problem from the coffee oils that build up on the brew group, and the two need different treatments.

What you'll need

Descaler or citric acid
Fresh water
Container for the output
Machine manual (optional)

Step by step

Check the manual for the machine's own descaling procedure.Many machines have a descale mode. Bean-to-cup machines in particular need their specific sequence followed.
Use the manufacturer's descaler, or citric acid at the stated dilution.Citric acid is cheap, effective and does not smell. Vinegar works but can degrade seals and the smell persists.
Fill the tank with the solution and run it through in stages.Stop partway and let it stand for fifteen minutes so the acid has contact time inside the boiler.
Run the solution through the steam wand and hot water outlet too, if fitted.Those have their own pathways which scale up independently.
Rinse with two or three full tanks of fresh water.This is the step people skip. Descaler residue makes the next several cups taste chemical.
Clean the water tank itself and let it dry.Tanks grow biofilm, particularly if water sits in them between uses.
Change any water filter cartridge on schedule.A filter reduces how often descaling is needed, but only if replaced.
Descale every one to three months in hard water.Slowing flow or a longer heat-up time are the practical signals that it is due.

Tips

Using filtered water dramatically reduces how often descaling is needed, and often improves the taste independently.
Descaling and cleaning are different jobs. If the coffee tastes bad rather than the machine running slowly, clean the brew group rather than descaling.
Empty the tank if the machine is not used daily. Standing water grows biofilm.

Common mistakes

Not rinsing enough afterwards — Descaler residue makes the next several brews taste chemical.
Using vinegar in a machine that warns against it — It can degrade seals and gaskets, and the smell is very persistent.
Descaling when the problem is coffee oils — Scale affects flow and temperature; oils affect taste. Descaling does not touch the oils.

Questions people ask

How often should I descale a coffee machine?

Every one to three months in a hard water area, twice a year in a soft one. Slowing flow or longer heat-up times are the signs it is overdue.

Can I use vinegar to descale?

It works chemically, but many manufacturers advise against it because it can attack seals, and the smell lingers for many brews. Citric acid or a proprietary descaler is better.