Some people behind the counters in cafés are not even allowed to adjust their grinders, let alone maintain their machines. They learn so little about espresso that they will be replaced by automatic push-button machines. Professional or home baristas who pride themselves on their espresso should know enough about espresso machines to keep them in good condition.
Each time you make an espresso, coffee grounds get on the screen and rubber gasket in the group. Some people recommend the "portafilter wriggle," that is, running water and wriggling the empty portafilter between shots to take care of this. However, this will not prevent gunk from accumulating on the gasket. Use a grouphead brush regularly (preferably after every shot, but minimally once a day for home use) to clean the group gasket.
Brewed coffee diffuses up the water path into the group during the extraction process. With time, the coffee oils accumulate and impart a stale coffee taste (a prickling on the palate) to every shot. Backflushing the machine removes this buildup. This is done by inserting a blind basket (a basket with no holes) into the portafilter, adding a teaspoon full of espresso machine detergent and running the pump for fifteen to twenty seconds. Typically this is repeated about five times without adding new detergent, followed by five plain water backflushes to rinse. Some people claim that just using a plain water backflush without detergent more frequently achieves the same goal. I have not found this to be true, and since coffee oils are insoluble in plain water, I see no reason why it should be. For home use, backflushing every two weeks or so is sufficient, while a café needs to do it nightly.
Backflushing only works on machines with a 3-way exhaust valve (these whoosh at the end of the shot and release the pressurized water remaining in the group into the drip tray). Smaller home machines do not have these. Such machines can be cleaned by placing a detergent such as CleanCaf in the tank and running it through the entire machine. Afterwards, the machine is rinsed by running lots of clean water through it.
Coffee oils also accumulate on portafilters, especially in the spout. You should let them soak overnight in a bowl filled with water and a table spoon of backflush detergent. Cafés do this every night, but once every week or two is enough for home usage.
Grinders should be cleaned by disassembling the burrs and blowing out the grind chamber with compressed air or a shop vac. When using compressed air, it helps to work with a plastic bag over the top the grinder since a lot of coffee flies around. Once a year, grind through some white rice to clear out the coffee oils accumulating on the burrs. After doing this, grind through some sacrificial coffee to clear out the rice powder.
For more details, see Espresso Machine Cleaning - Why, How, and When.
As the owner of a home machine, you should be able to change out the group gasket and screen, fix minor leaks and electrical glitches, and flush and descale the machine. However, the details of this are machine dependent. Refer to your owner's manual, the links in this article, and the resource section on this site.
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