An abused or fatigued group head gasket—often caused by over-tightening—will periodically lose its seal and leak during a shot.

What Happens on the Graph

When a gasket fails to hold a proper seal, several clear anomalies show up on the shot profile:

Pressure Drop: As the pump begins building pressure, the worn gasket gives way. Instead of climbing smoothly, the pressure suddenly drops or falters.

Spike in Flow Rate: Under normal conditions, the flow rate should decrease as the pressure climbs. With a leak, water bypasses the coffee puck around the sides of the gasket, causing a sudden spike (boom) in the flow rate.

Sudden Water Volume Increase: Because of the leak, an unexpected surge of water rushes into the puck and the cup all at once.

The Recovery

As the machine continues to build pressure to reach its target profile, the increased force can sometimes push the gasket back into place, temporarily resealing it. When this happens, the pressure will finally rise to its goal and the flow rate will stabilize back to a normal downward trend.

A normal, healthy shot should have a smooth, steady rise in pressure and a clean, gradually decreasing flow rate line without these sudden jagged spikes.

Here is a screen shot of this leaky gasket espresso shot:

I forgot to mention that you can see that the shot ended about 7 seconds earlier than desired, because it hit the requested final "in cup weight" sooner, due to the water drips.

If this problem happens to you, just solve it by swapping the espresso gasket. You can find them here: https://decentespresso.com/c?filter=gasket

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