Coffee oils and residuals tend to deposit in the internal circuit of your machines, and especially with E61 coffee machines like Rocket, ECM or Lelit it is vital for maintaining the machines in great working condition.
The espresso cleaner (generally called Cafetto) will remove the old coffee oils and deposits that can cause your coffee to taste bitter and rancid. It will also prevent coffee from building up on the shower screen that eventually plugs it up. If you ever see small high-pressure streams of water coming from the shower screen you know it is blocked and is channeling through the water. A that point it will be too late and a new shower screen will be required.
The bottles of Espresso Cleaner come with handy instructions but we will go over the best method in our opinion with the following paragraph.