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Mushroom (E61)
The internal brass piston in an E61 group that the cam pushes — controls inlet flow and exhaust to the drip tray.
Category: Espresso Machine — Groups & Brew Path
The mushroom-shaped piston inside the E61 brew valve. Lifting the lever pulls the mushroom upward, opening the brew path; lowering the lever drops it back and seals the path.
Why it matters — The mushroom is the heart of the E61 mechanical design. A worn or scaled mushroom causes brewing inconsistencies, valve leaks, and dripping after the shot.
Good to know
- The mushroom is a standard replacement part during an E61 rebuild — every 5–10 years for home use, more often for café use.
- Symptoms of a failing mushroom: dripping from the group after the shot ends, sticky lever action, or pressure leaks during pre-infusion.