How do I clean a coffee machine?

Descaling versus cleaning, how often each is needed, and the parts that affect taste most — including the ones people never clean.

Difficulty: beginner
Time: 45 min
Read: 3 min

Short answer

Two different jobs: descaling removes mineral scale from the water path (every 1–3 months in hard water), and cleaning removes coffee oils from everything the coffee touches (weekly). Rancid coffee oil is the most common cause of a machine that suddenly makes bitter coffee.

People descale and assume they've cleaned. They're different problems in different places. Scale builds up inside the boiler and pipes and affects temperature and flow; coffee oils build up on the brew group, basket, shower screen and carafe, and go rancid. The second one is what you taste.

What you'll need

Descaler or citric acid
Coffee machine cleaner or bicarbonate of soda
Brush and cloths
Backflush disc for espresso machines (optional)

Step by step

Identify which job you need: bad taste is usually oils; slow flow or poor temperature is usually scale.Doing both periodically is right, but knowing which fixes what saves time.
For weekly cleaning, wash everything the coffee touches in hot soapy water.Basket, carafe, filter holder, lid. Coffee oil is not water-soluble — it needs detergent.
Clean the shower screen and group head on an espresso machine.Wipe after every session and brush the screen weekly. This is where oil accumulates most.
Backflush an espresso machine with a blind disc and cleaner if it has a three-way valve.Check your machine supports it — not all do, and backflushing one that doesn't just makes a mess.
For descaling, run the manufacturer's descaler or a citric acid solution through the water path.Follow the machine's instructions. Vinegar works but can damage seals in some machines and the smell lingers.
Rinse thoroughly with two or three full tanks of fresh water afterwards.Descaler residue tastes terrible and it takes more rinsing than seems necessary.
Clean the water tank and let it dry, and change any water filter on schedule.Tanks grow biofilm, especially if water sits in them. Empty it if the machine isn't used daily.
Descale every 1–3 months in hard water, monthly-ish for cleaning.Softer water areas can stretch descaling considerably. Watch for slowing flow as the signal.

Tips

Using filtered water dramatically reduces how often you need to descale, and often improves the taste independently.
If coffee suddenly tastes bitter or 'off' with no other change, clean before you descale — rancid oils are the usual culprit.
Don't put a chrome or aluminium part in the dishwasher unless the manual says so; dishwasher detergent damages both.
Grinders need cleaning too. Old oils in a grinder taste rancid regardless of how clean the machine is.

Common mistakes

Descaling but never cleaning — Scale affects flow and temperature; oils affect taste. Descaling doesn't touch the oils.
Not rinsing enough after descaling — Residue makes the next several cups taste chemical.
Using vinegar in a machine that warns against it — It can degrade seals and gaskets, and the smell persists for many brews.
Leaving water in the tank between uses — Standing water grows biofilm, which affects both taste and hygiene.

Questions people ask

How often should I descale?

In a hard water area, every one to three months. In a soft water area, twice a year may be enough. Slowing flow or a machine taking longer to heat are the practical signals.

Can I use vinegar to descale?

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