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The one thing you should never do with your coffee machine

This no-no will clog up your machine and leave you with bad-tasting coffee.

Last updated: 11 September 2023

Your coffee machine dispenses a heavenly, life-giving elixir every morning, but what you may not know is that inside, it could be a gunky hellmouth of sludge with a side of yeast, bacteria, mould – and the occasional cockroach

Yep, we said it: mould. And cockroaches. 

Aside from the obvious yuck factor, leaving your coffee machine dirty will send it to an early grave and – perhaps even worse – ruin your coffee. 

Not cleaning your machine is the biggest coffee crime you can commit

Adrian Lini, CHOICE coffee machine expert

"Not cleaning your machine is the biggest coffee crime you can commit," says CHOICE coffee machine expert Adrian Lini

"It'll reduce the lifespan of your machine, and also mess up the taste of your coffee."

Here's what can happen if you forget to clean your espresso machine. 

Your steam wand will be gross

When you're frothing, the steam wand gets covered with milk. Leave it to sit and it'll turn into putrid, rotten milk – which will end up in your next coffee. Ugh. 

And it's not just on the outside: if you don't purge the steam wand there might be residual milk inside too. 

This doesn't just apply to cow's milk, so even if you're a soy or other plant milk drinker you shouldn't be complacent. 

If the milk dries, it's much harder to clean off, so give it a quick wipe and run some steam through once you're done. 

You'll get that burnt coffee flavour

Stale, burnt coffee is the downfall of a good brew. 

Even after you've made an espresso and emptied the portafilter (that's the bit you put the ground coffee into), there'll still be some lingering coffee grounds left in the group head (the bit you put the portafilter into). These leftovers will become stale and can burn from the heat. 

Run some water through after you've finished to get rid of the remaining grounds each time. You can rinse the portafilter under the running water while you do it. 

Look at you, you're multitasking before you've even had a coffee!

The drip tray will grow mould

This is one part of your coffee machine that's easy to ignore. But it's seriously worth the effort to clean it often. 

The combination of water and coffee grounds that fester in your drip tray is the perfect environment for bacteria and mould to do their thing. And it's appealing to cockroaches, too. 

Keep things fresh by emptying it daily if possible, and rinse it with hot water so there's nothing left behind to feed the mould.


The contents of my knockbox after a couple of days. Don't be like me.

More mould in your knockbox

Your knockbox can quickly become a petri dish if you let it sit for too long. 

"Coffee grounds can become mouldy really quickly – sometimes in as little as 12 hours," Adrian says. 

"Toss out the contents of your knockbox every couple of days at a minimum. You can compost coffee grounds, add them to a worm farm or put them in your garden beds."

Clean and enviro-friendly – what's not to like?

Rancid oil in your coffee grinder

Your coffee is only as good as your beans, and if your coffee grinder is clogged up with stale beans your brew will always be a bit average. 

Also, coffee beans are oily and as the oil builds up it can turn rancid, which means – you guessed it – bad coffee. 

You don't want to use water in your grinder, though, just take it apart and use a dry brush to clear out the built-up coffee grounds. If you're feeling really committed you could even use your vacuum. 

A small paintbrush or soft-bristled toothbrush will do the trick. Just make sure the toothbrush is clean, unless you fancy a minty coffee. 

Backflushing your machine

Have you ever wondered what that little filter without holes is for? It's called a blind filter or blind basket and it's used to 'backflush' your coffee machine.

Backflushing diverts the water pressure back through the grouphead and releases it from the valve into the drip tray, cleaning out built up coffee deposits and oils along the way. 

For most machines, doing this once a week is enough, depending, of course, on how often you use it. You should always read the manual and follow the instructions for your particular machine before backflushing or descaling.

Gunk will build up inside your machine

It's what's inside that counts – and that's especially true of your coffee machine. It might be shiny on the outside, but what's lurking within is more important. 

Most manufacturers will recommend that you descale your machine regularly, whether annually or every few months to clear out any calcium deposits which have built up inside the machine. Be guided by the manual and make sure you schedule this accordingly. 

Any gunk that's inside your machine is going to end up in your coffee which, aside from the ick factor, will affect the flavour of your cuppa. Regular cleaning, backflushing and descaling will help get rid of built-up oils, coffee grounds and deposits. 

Just remember to run a few shots through your machine and tip them out after descaling – they'll taste gross and you definitely don't want to descale your insides!

We care about accuracy. See something that's not quite right in this article? Let us know or read more about fact-checking at CHOICE.

Stock images: Getty, unless otherwise stated.