I'd like to understand something I observe happening when pulling shots on my Gen 3 La Pavoni with different coffees dialed in to different grinds. When I lift the lever a single time to pre-infuse, then pull the shot after about 8 seconds, I find that the amount of liquid I get in the shot varies quite a bit from coffee to coffee.
For each shot, I grind 15g of beans. The results I get for different beans are as follows:
Sulawesi, roasted City+, pretty hard/dense bean, roasted a bit finer: 25-27g
Natural processed Guji Hambela roasted City+, more delicate/softer bean, roasted a little coarser: 17-20g.
These grinds are what I've dialed in for best flavor after experimentation. To satisfy my taste in espresso, I compensate with an appropriate amount of Fellini pumps to reach around 37-40g, and my result then is pretty enjoyable.
Mostly out of curiosity, I wanted to get some insight into what's causing the differing amounts of espresso output. Intuitively, I would've expected the coarser grind / softer bean to create more of a pressure disparity between the group / boiler and thus result more water flowing from the boiler. But that's clearly not what's really happening