Clean the group head under the screen by scrubbing with your Scotch Brite pad nightly as well. D. Group Gaskets Clean the group head gaskets with a small stiff brush when you have the screens out. These gaskets are the ones that the porta-filter snugs up against when the group handle is put into place, creating a sealed environment to contain pressurized brewing water. On a nightly basis, remove steamer tips and clean apertures with a pin or brush. It may be beneficial to run a small brush up the wand as well.
Many technicians recommend submerging the steamers in water overnight to soak off crusties.
The problem with this is that if the power goes off in the building the boilers cool off. The cruddy water is then sucked up the steamer wand and into your main boiler. Not a pretty picture. These procedures, if performed by your closing crew each night, will not only help keep the coffee sweet, they also will increase the longevity and reliability of your espresso machine. Old Italian Folk Remedies A technician that I know has had good luck stripping scale build and rancid milk from inside espresso boilers and delivery lines by flushing the machine with mild lemon juice.