First, here is some background on my machine. My Gaggia Coffee is similar to the Classic but has no three way solenoid valve. Instead it uses a spring and ball in the water path between the dispersion screen and the boiler. This operates as an expansion valve creating resistance the pump must overcome before water will exit the shower head and contact the coffee. I have made no adjustment to this unit either so pressure has not been adjusted or optimized in any way.
When pulling a shot I listen to the pump - it will make a lower toned sound at first then gradually as pressure builds the tone increases in pitch and the pump smooth's out. Without intervention the espresso will start flowing soon after the pump sound smooth's out. What I have been trying lately is to stop the brewing at this point for a couple seconds. I know when I have an empty portafilter in the unit when it makes this sound water will start flowing out the bottom of the empty portafilter. From this I deduce that water is already sitting on top of the puck at the moment I interrupt the pumping process waiting for extra pressure to push it through.
What happens next is where it gets interesting for me and I would like to see some honest feedback from you - my fellow single boiler espresso machine users. I find when I hit the switch again after a couple moments the crema looks thicker, the flow is slower but builds to a thicker stream, and the shot tastes better. I do know with my machine the "boiler ready" light will cut off about the same time the pump sounds higher toned - I use this as my timer - I cut the pump back on when the green ready light cuts back on. The pump on my machine sounds less robust when the heating element is active so this pre-warming while pre-infusing usually keeps the element off through all but the tail end of the shot and if it pulls a little quick, off through the entire shot.
If anyone else can confirm my experience, or has nothing even close happening, please post here so we can learn from each other. Thanks in advance.