In a day to day operation of a cafe, the barista [if they are professionally trained] will definitely clean the grouphead by back-flushing them with specially-formulated detergent.
But how often do they give the shower screen a proper scrubbing?
The water you use to brew espresso will pass through the shower screen just before it came into contact with the coffee ground. Imagine your shower screen that is dirty and lined with rancid oil and coffee stains from months ago. It is no surprise your coffee leave a bad taste in your mouth.
But more often than not, when you look at the screen from below, the screen looks clean. That’s because the outside is fairly easy to clean. Just using hot water and a heat-resistant brush will make the external looks good.
It has been a standard practice for a properly trained barista to clean the grouphead everyday with espresso machine grouphead cleaning detergent. And if they do a thorough cleaning everyday that include back-flushing the grouphead with detergent, the grouphead including the shower screen will be up to standard for months. But some may asked, do we need to totally remove the shower screen to clean the inside of the screen?
Here are a few examples of the shower screen used for 4 months.
[#1: 4 months without back-flushing with special detergent]
In Figure #1: This is a shower screen on a machine where the grouphead was not cleaned nor back-flushed with detergent. They did clean them with a brush and hot water but did not use the appropriate detergent. While from the outside, it looked clean and shiny, the underside (or inside) of the shower screen is very dirty, stained with thick rancid oil and clogged with fines from the coffee ground. Every time when espresso is extracted, the water have to pass through the fines and rancid oil before coming in contact with the fresh coffee ground. The resulting espresso is a mixed of fresh coffee flavor [assuming you are using fresh roasted coffee] and stale and rancid coffee oil accumulated over the months.
[#2: 4 months usage but cleaned everyday by back-flushing with detergent]
In Figure #2: This shower screen on the machine where the grouphead was cleaned and back-flushed everyday with detergent. Here, you can see a very slight stain of light brown but not visible clogging of the shower screen by fines. The impact of bad flavor cross contaminate from stale and rancid oil to your fresh coffee ground will be minimal.
[#3: Removed from grouphead and properly cleansed]
What would KF Chan recommend? Do you need to remove and clean the shower screen every day? I would say it is not necessary to remove the shower screen for cleaning every day. I would recommend to remove the shower screen every 3-4 months, with the maximum of 6 months interval if you are lazy.
You pay good money for fresh roasted coffee beans. Make sure the taste is not compromised by dirty espresso machine.