Why Does an Espresso Puck Stick to the Group Head?

An espresso puck usually sticks to the group head for three reasons: too large a dose, leaving the portafilter locked in too long after the shot, and knocking the puck loose. Of these, failing to remove the portafilter promptly is the most likely trigger, because the puck stays pressed against the shower screen and dries out.

Dose matters less than many people assume. An oversized dose leads to sticking roughly one time in ten, and the fresher the beans, the greater the chance. Occasional sticking does not change flavor if extraction parameters sit in a reasonable range, though channeling can still hurt what's a espresso shot delivers in the cup.

When making espresso, the puck sometimes sticks to the shower screen of the group head—what exactly causes this? And does it affect the flavor of the coffee? This article starts from three common causes and analyzes them one by one: too much coffee grounds, not removing the portafilter promptly after extraction, and the puck being knocked loose. Front Street will also draw on its own practical experience to explain the burnt-bitter taste problem that may arise when the puck comes into contact with the shower screen, as well as the impact of channeling on espresso performance, helping you judge in your daily output when there is no need to worry and when parameters need to be adjusted.

Too much coffee grounds

This is the most easily noticed cause, and at the same time its impact is relatively the smallest. Front Street has mentioned that under ideal conditions, a thin gap should remain between the surface of the puck and the shower screen on the group head, and during extraction the coffee puck expands slightly after being wetted.

If the dose is too large, after locking in the portafilter, the surface of the puck will directly press against the shower screen. At the end of extraction, the group head will suck back excess water in reverse, which easily makes the puck stick to the group head.

However, a large dose does not necessarily cause the puck to stick. Usually, the puck sticking to the group head is more or less related to too large a dose, but the probability of it being the direct trigger is actually not that high—about 1 time in every 10. The fresher the coffee beans, the greater the chance of sticking to the group head due to too large a dose.

Removing the portafilter some time after extraction ends

This is the situation most likely to cause the puck to stick to the group head. If the portafilter is not removed immediately after extraction is completed, the puck will be pressed against the shower screen and its moisture dried out, gradually binding together.

Too large a dose, plus not removing the portafilter promptly after extraction ends—when these two are combined, it becomes very easy for the puck to stick to the group head. As long as the extraction parameters are within a reasonable range, the puck occasionally sticking to the group head will not affect the flavor performance of the espresso. If this happens frequently, then you should reduce the dose a bit and make adjustments to the parameters.

Just as with the dose used at Front Street, it will also be somewhat more than the capacity specification of the filter basket. If the portafilter is locked onto the group head and then removed after waiting 10 seconds, the hot, moist shower screen will take away some of the coffee grounds.

Therefore, after locking in the portafilter, if the puck contacts the shower screen and extraction is not started for a long time, the surface of the puck will be “scorched” by the high temperature, producing a burnt-bitter taste. But if the extraction button is pressed immediately after locking in the portafilter, no abnormal flavor will appear.

The puck has been knocked loose

There is another situation: after distributing and tamping are completed and before locking onto the group head, an accidental bump occurs, creating a gap between the puck and the filter basket. Likewise, when the dose is too large, it is more likely to stick to the shower screen. In this case, because the puck and the filter basket are not tight enough, channeling will occur, thereby affecting the performance of the espresso.

The above content is compiled by CoffeeHunters, a coffee news website.