Coffee machine needs cleaning or descaling
Flow has slowed noticeably over time, coffee tastes increasingly off regardless of recipe changes, or visible mineral scale is present.
Applies to: Espresso machine, Moka pot
Safety note
Always unplug electrical machines before cleaning any part near the heating element or electrical components. Never dismantle a sealed pressure or heating component — for anything beyond routine external cleaning and manufacturer-approved descaling, consult the manufacturer manual or a qualified technician.
Telling coffee oil from limescale
CoffeeHQ explanation
A coffee machine collects two kinds of deposit, and they come from different places. Coffee oil and fine grounds build up wherever brewed coffee touches metal: the basket, the shower screen, the group, the spouts, a brew unit, a carafe. The oil turns rancid within days and gives every cup a bitter, stale edge. Limescale is mineral from the water and forms where water is heated: the boiler, the thermoblock, the pipes. It has little taste and slowly strangles the machine.
The remedy for one is not the remedy for the other. Detergent is sold for coffee oil and descaler, an acid, for mineral scale, and neither is sold for the other's job. The commonest maintenance mistake is doing the wrong one carefully.
Causes, most likely first
There are 2 likely causes, listed with the most probable first. Work down the list and change one thing at a time, so that when the problem goes away you know which change fixed it.
Cause 1 of 2 · Commonly the cause
Mineral scale buildup from hard water
- How to check
- Has it been longer than the manufacturer's recommended descaling interval?
- What to change
- Descale following the manufacturer's instructions and recommended descaling product.
Cause 2 of 2 · Commonly the cause
Coffee oil residue buildup
- What to change
- Clean or backflush per the manufacturer manual; do not substitute an unapproved cleaning product.
If none of these fixes it
If you notice a burning smell, exposed wiring, persistent leaking, or the machine won't power off, unplug it immediately and stop use until it has been inspected by a qualified technician.
Work through it for your setup
The causes above are general. These go to the part of a diagnostic that takes this symptom one check and one change at a time.
- What builds up: coffee oilsWhat it does to the cup or the machine, and how you would notice
- What builds up: scaleWhat it does to the cup or the machine, and how you would notice
- Care, by sign and by the manual: espresso machineThe habit with every use, what to check and what triggers a job
Let the symptom choose the job
If the coffee has turned bitter, stale or rancid while the machine itself runs normally, the problem is oil: clean. If the machine has become slow to heat, weaker in flow or steam, or noisier, and the coffee tastes as it always did, the problem is scale: descale, if your manual permits it. If a warning light is prompting you, the manual says which of the two that light means; on many machines the two prompts are separate.
What cleaning means on different machines
Tendency, not a guarantee
- Espresso machine
- Wash the basket and portafilter, brush the shower screen, and backflush with detergent if the machine has a three-way valve. Purge and wipe the steam wand every time.
- Bean-to-cup machine
- Rinse or run the cleaning cycle for the brew unit as the maker directs, and clean the milk system after every use; milk residue is the urgent one.
- Filter machine and kettle
- Wash the basket and carafe, where oil collects. The heating side only ever sees water, so its problem is scale.
- Capsule machine
- Empty and rinse the capsule container and drip tray, and run a water-only cycle. Descale on the maker's prompt.
Easily confused with
- Over-extracted coffee — Over-extraction responds to a coarser grind or a shorter brew. A rancid bitterness that survives every recipe change, with every coffee, is the equipment.
- Scale as a standing problem — If you are descaling often, the question is no longer how to descale but what water you are putting in.
What not to change at the same time
Do not clean and descale in one session and then judge the coffee. Do the one the symptom points to, rinse, and taste; if the fault remains, you have learned it was the other.
How to tell it is fixed
After cleaning, the stale edge is gone from the first cup. After descaling, the machine heats and flows as it did when newer; the taste may not change at all, and that is expected.
Cleaning and maintenance planner — Enter your machine type, how much you use it and your water hardness. It lays out which jobs are cleaning and which are descaling, and names no chemical.
What to change
Specific adjustments for this symptom, with what each one trades off.
Work it out
Interactive tools that take you through this one change at a time.
Learn the technique
Step-by-step guides to the skills this problem comes from.