Hi.

I have a Gaggia Classic (single boiler) and it seems that the pressure can be gradually dropped (but not sure how much) during the shot by opening the steam wand. I use a Hario V60 Kettle and then the exiting water from the wand can then be reused. The temperature will probably also dropped since the boiler in this machine is small but it looks like an easy way to maybe do "pressure profiling." I was thinking that maybe in a E61 brew head, a butterfly valve maybe could be added in the same fashion or maybe tapped in another point of the system (before the hot brew boiler).

I tried and it does something but it is just an idea.

Cheers

See My Experiment in Variable Brew Pressure via Steam Wand for Single Boiler Espresso Machines
by Tim Eggers from March 2007

Thanks for the links.

I was thinking that if the valve was located before the boiler (cold side), and the released water was exiting to the inlet, then the temperature would not drop during the shot. So maybe an extra knob (like the steam wand knob) could be added to control the pressure by using a bypass valve.

Cheers

I can confirm that putting the valve on the cold water side of the boiler does work, quite well in fact. I used a needle valve (I think that is what it is called) that allowed very good control over the brew pressure.

Here is a video of a 'spring lever' type of pressure profile, i.e. 9 bar at the beginning and then falling off as the shot progresses: 9 Bar then falling