La Marzocco GS3 - issues with pre-infusion and a question on dosing/volume
When I first had my machine, 4 months ago, the pre-infusion was fine. I have the MP version. I would take the paddle right to the edge, just before it activates the pump and the pressure would drop rapidly, and I could hear fluid possibly being let sit on top of the puck. This improved the quality of my coffee by reducing channeling.
For the last 1 month or so, that sweet spot for pre-infusion seems to have disappeared. I move it ever so carefully, but still can't achieve the point when the pump is off but fluid is pre-infused. It is very strange.
On a more beginners level: I am using a 17g basket. I weigh the ground coffee to make it 17g exactly when I am grinding before I tamp. I like coffee to be relatively strong, so I use 17g for 1 shot. Given that I am only making one shot, should I be aiming to still achieve only 30g of coffee in 30 seconds? As you can also use the 17g basket for a double shot, but that makes no sense to me, as I don't know how I would go about achieving 60mLs in 30 seconds with the double shot spout. The ground would have to be VERY coarse.
Appreciate the help.
I'm not sure if you've been able to remedy your problem, but you can adjust the pre-infusion point and pump activation points based on the position of the microswitch. This can be easily done with by removing the grouphead cover and loosening the the nuts that the microswitch is mounted on with a 5.5 nut driver. (It is easier if you have two, but I used a wrench on the other side to calibrate mine).
I've recently ordered the parts to install the strada MP's pressure gauge to my gs3, which I hopefully should receive soon, which should allow for greater control.
With regards to your dosage concerns, I think ultimately it is up to your taste preference but personally i do around 25ml in 28s from a 18g dose with the beans I normally use.
On a side note, I only got my GS3 recently too and recently experienced the paddle somehow being "slippery" in a sense. I'm wondering if this is normal or is it a result of my tinkering with the microswitch positioning. Functionality still remains albeit with a somewhat strange feedback from the paddle now feeling a little different.