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Updated for 2021.
Backflush. What a funny combination of words. For the new espresso machine user this obscure play on words has been one of the great mysteries of the espresso world. This tech tip will give you the inside scoop on backflushing without having to go through the pains of asking.
Backflushing is the process used to clean out the shower screen, brew group and three-way valve. Backflushing can only be done with machines that have a three-way valve. The three-way valve is a small valve that opens up and releases the water pressure off of the coffee and deposits it into the drip tray when the brewing process is complete. When we backflush we utilize this pressure release to blow cleaner up into the brewing components.
The cleaner 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 plugged and is restricting the water flow.
Go ahead and remove the screen and hold it up to the light. You will be amazed at how any water gets through it at all. The bottles of cleaner come with instructions but I will go over one method briefly in the following paragraph.
Any semi-commercial or commercial machines such as the ECM, Rocket Espresso or Pasquini should be backflushed on a regular basis. When the machine is being used in a commercial application the machine should be backflushed at the end of every day. For home users who are real particular, backflushing could be done every day though once or twice a week would be adequate.
If you have one or both of the following symptoms your three-way valve may need cleaning.