If your espresso machine has started producing coffee that tastes a little funky, it’s time to clean it. If the manual has specific cleaning instructions, you should probably follow those. Otherwise, here are some general tips for keeping it clean.
So fresh and so clean
The filter basket and portafilter should never be placed in a dishwasher, as the metal will corrode. Use mild soap on these and wash them by hand.
Cleaning the “shower head” in the group area is the easiest part. While it’s simplest to use a rag or a paper towel to clean the group head, it’s better to use a brush for this purpose to avoid scratches. The gasket around the head will degrade faster if it’s dirty, so you should make sure to wipe this clean often as well.
Occasionally, minerals in the water will build up in the machine and will affect the taste. You can buy espresso machine cleaner or you can simply brew one part distilled white vinegar with one part water (through an empty filter basket, of course!) I should warn you now that this will stink, and that you will have to run water through the machine two or three times afterwards to clean out all the vinegar. Drip coffee machines should also be cleaned with vinegar (unless the manual states otherwise.)
DO NOT put soap inside the machine — especially dishwasher detergent — as this may cause corrosion and will only make the problem much worse.
That’s almost everything. My last tip is fairly obvious: don’t leave water in your machine when you’re not using it. Water will cause rust and promote bacteria build-up. Plus, all your espresso will have that icky stale water taste.