Over the last couple of months, my puck occasionally sticks to the shower screen on the group head. I have not changed coffee, dosing, grind, or technique. I am using a La Marzocco GS3 paddle and a Mahlkonig K30. Any ideas what is causing this?

I believe this is primarily due to the puck being wet and pourous, but may also be related to the dose size, with a larger dose being more likely to expand, hit the shower screen and adhere to it when when pressure is released.

On my GS/3 AV, which is modified for flow and pressure profiling, this is more likely to happen with long, slow preinfusion (Slayer-like) shots. The puck opens up during the long, slow preinfusion, which is what allows the finer grind, and fills with water before being compressed, as opposed to being quickly compressed when preinfused at the much faster stock flow rate.

You can also get a wet puck when pulling low brew ratio shots (Lungo), and even wetter if you pull Lungo Slayer shots.

Although sometimes the almost-intact puck is drawn up and adheres to the shower screen when pressure is released, usually some of the puck remains in the basket, implying that the vacuum has pulled the puck apart.

When I pull with the stock flow rate, the puck is drier, stays in the basket and tends to be intact when I knock it out.

Whether a wet puck sticks with a given bean, dose, grind, technique, etc., appears to be somewhat random.

[EDIT: It occurs to me that changes in ambient humidity could explain why you're suddenly getting sticky pucks. It could be affecting the grind (e.g., making it more or less clumpy, which might affect the integrity of the puck.)]

On my Robot the puck will stick to the screen if I let the portafilter sit for a while after the shot, thinking that with the heat from the pull the puck dries out fast and sticks to the screen. Any chance it only happens when the setup sits a little longer than usual?

I don't know the inner reasons why, but when I does too low for my basket (i.e. 17g or less in double) the puck might stick. Anything 18g and over is fine. The more coffee over 18g, the cleaner the puck comes out of portafilter in my knock box.

txrpls wrote:Over the last couple of months, my puck occasionally sticks to the shower screen on the group head. I have not changed coffee, dosing, grind, or technique. I am using a La Marzocco GS3 paddle and a Mahlkonig K30. Any ideas what is causing this?

I don't have this issue. However, I start putting AEROPRESS paper filters on top of the puck. This reduces the amount of gunk going back up into the group.

It happens. My old Elektra A3 did it now and then and my GS3-MP will once in a blue moon. Nothing to worry about. Keep in mind at the end of the shot and pressure dump you are going from 130ish to 0 PSI. If the puck is dense you could get a vacuum above the puck which can suck it up out of the basket and onto the shower screen.