Whether you own a Kees Van Der Westin Mistral, or Rancilio Silvia, you need to have a good cleaning regiment. I know what you're thinking, "But I wash the portafilters once a week, whether it needs it or not." Well, not good enough! If you're a home user or pro-barista the following recommendations apply. I'm going to outline a schedule for cleaning your machine on a yearly, monthly, weekly, daily and even hourly basis.
Hourly? Yes! Hourly! You probably never thought about doing anything to clean your machine every hour, but did you know that coffee oils go rancid after 45 minutes? So, every shot you pull, hot espresso is rolling over those nasty oils and particles, picking up that bitter flavor (oil is oil soluble) and putting it right in your cup! This applies if you pull 1,000 shots an hour, or one double every hour. Get that oil out of there!
At the end of each session, perform a "wiggle rinse" to wash away grinds from the dispersion screen, and then do a quick clean water backflush. Every hour you should scrub the inside of the portafilter and the portafilter basket. I like using a Scotch-Brite pad myself, but any tool that will get the job done is fine. And since you've got the portafilter off, clean the shower screen and gasket with a group brush.
If you are using an inline water filtration system, the kind that use cartridges, check to make sure they still work. Some cartridges are not designed for high volume output and will start adding undesirables to your water supply instead of taking them out. This will not only give your espresso a chemical flavor, but can also add calcium deposits to your machine.
Descale your espresso machine once a year. No matter how good your water filtration may be, you're still getting calcium in your boiler tank. While small amounts of calcium won't alter the flavor of your espresso too much, over time that small amount will grow into a large amount causing a very bitter flavor in your cup and eventually causing damage to your machine.
Remember, it doesn't matter if you have a $15,000 machine or a $100 eBay find. If you take all the right precautions you can enjoy your machine for many years to come. But, keep in mind, with a machine so clean, you'll have one less thing to blame if you're not satisfied with the taste of your espresso.
One of the issues with comparing home to commercial is that sometimes the same considerations don't directly apply. At home, you're not banging out a shot every 30-45 seconds; you're not usually working with broken in portafilters; you're not dealing with machines that are backflushed with (large) amounts of cleanser at least once every day. That being said - there are some important things to learn and apply here.
First - if you are working with broken in and/or chrome-stripped portafilters, it is very advisable to pull a garbage shot before you start serving espresso in order to season the brass.
Second - you should not rinse your baskets before pulling shots but rather dry-wipe them. This is not a cleanliness issue - but rather a water issue. You want totally dry baskets before you dose. In addition, portafilters spouts can trap some water in the bottom joint if you rinse, which will end up in the shot.
A couple other things...
If you want to understand the rationales - stick a cup under your portafilter when your machine is clean. Pull water (no coffee) into it. Taste. Do when "kind of clean" and "clean enough" as well. You really want to make coffee with that? In the end, all these recommendations are about the quality in the cup and the protection of the machine. The former should be discernable at every tasting, but the latter is not (until it is too late). Take it seriously.