If you are having issues maintaining puck integrity throughout the duration of the shot (i.e. due to poor grind quality or when pulling light roasts), this pre-infusion mode only technique can be used as an alternative to an OPV adjustment
NOTE: This guide is useful for Breville Infuser and Barista Express users, as these machines have an in-built gauge that will guide your dialling in. Additionally, this technique requires the user to hold the machine in pre-infusion (PI) mode throughout the shot, which appears to only be possible on machines with the older thermoblock design. The newer “thermojet” machines like the Bambino Plus and Breville Pro machines do not seem to have the ability to hold PI mode for more than 10 seconds. As such, this PI-only technique is unfortunately not possible on these machines.
If you have any of the other Breville machines, or any espresso machine with a vibratory pump for that matter, an alternative to achieving better control of puck pressures is via modifying your machine with a dimmer.
With your cleaning disc/blind disc in the portafilter, hold down either the 1-cup or 2-cup button to keep the pump in PI. Let pressure build until the needle stops moving (this may take around 30s). Take note of what pressure is reached when the needle stabilises - this is the max ‘PI’ pressure your machine can achieve. To stop the shot, let go of the button and press it once more.
If your machine was able to build at least 9-10bars of pressure in PI mode, this technique could work for you.
These are the approximate pressures (in bar) that correspond to marks on the pressure gauge.
Press and hold the 1-cup or 2-cup button for the duration of the shot. Do not let go of the button as this will trigger the pump to engage fully, causing puck pressures to exceed desirable levels. When you reach your desired yield, release and then immediately press the button again to stop the shot.
Dial in your shot as you normally would, grinding fine/coarse enough to achieve enough puck pressure while also maintaining adequate flow through the puck to reach your desired yield within 60secs. It is normal for pressure to build to 9-10bars at the start of the shot, then gradually fall to 6-8bars as the puck erodes throughout the shot.
Note that Breville machines (with the exception of the Breville Dual Boiler) have a 60sec shot time limit.