There's been lots of debate about pre-infusion in machines, and how it's done and for long to do it.
This is how it works on my commercial Grimac Eclisse, which may be of some use.
Pump: rotary
Water: tank (though normally plumbed in to mains)
Brew pressure: 9 bar
Idle pressure: 0 bar
Controls: volumetric touchpads
Valves: solenoid
Once the brew touchpad is pressed, the pump shoots up pressure to 9 bar instantly. No ramping, no hesitation.
Under 2 grams of water is released from the shower screen for under 1 second -- the time it takes for the solenoid valve to click on and off.
The solenoid valve opens the group stem to release pressure to the drip tray and then immediately closes.
In this cycle the pumps is still pumping.
Water then resumes coming out of the shower screen at 9 bar for the remainder of the shot.
That is approximately 30 seconds from the moment I press the touchpad to when the pump stops.
So...is two grams of water for 1 second an adequate pre-infusion to saturate the puck? Probably not according to theory.
Is pressure at 9 bar too much for a pre-infusion? You could argue that sort of pressure defeats the purpose of gently wetting the puck.
However, with the portafilter removed and the machine cold, I've put my hand under the shower screen for both this pre-infusion and normal brew cycle and I can say there is no jet-blast force. It is all very gentle.
How does the puck take it? Pucks always come out solid, well-shaped with no deformity (unless I screw up the dose).
Note that the machine being volumetric, controls the brew cycle according to how much water has gone through the inline flowmeters. Not according to how much time has elapsed.
A digital battery clock clipped to the warming tray tells me timing. Not the machine.
This is how it works on my commercial Grimac Eclisse, which may be of some use.
Pump: rotary
Water: tank (though normally plumbed in to mains)
Brew pressure: 9 bar
Idle pressure: 0 bar
Controls: volumetric touchpads
Valves: solenoid
Once the brew touchpad is pressed, the pump shoots up pressure to 9 bar instantly. No ramping, no hesitation.
Under 2 grams of water is released from the shower screen for under 1 second -- the time it takes for the solenoid valve to click on and off.
The solenoid valve opens the group stem to release pressure to the drip tray and then immediately closes.
In this cycle the pumps is still pumping.
Water then resumes coming out of the shower screen at 9 bar for the remainder of the shot.
That is approximately 30 seconds from the moment I press the touchpad to when the pump stops.
So...is two grams of water for 1 second an adequate pre-infusion to saturate the puck? Probably not according to theory.
Is pressure at 9 bar too much for a pre-infusion? You could argue that sort of pressure defeats the purpose of gently wetting the puck.
However, with the portafilter removed and the machine cold, I've put my hand under the shower screen for both this pre-infusion and normal brew cycle and I can say there is no jet-blast force. It is all very gentle.
How does the puck take it? Pucks always come out solid, well-shaped with no deformity (unless I screw up the dose).
Note that the machine being volumetric, controls the brew cycle according to how much water has gone through the inline flowmeters. Not according to how much time has elapsed.
A digital battery clock clipped to the warming tray tells me timing. Not the machine.



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