I agree that some sort of preinfusion is happening but to paraphrase Spok “It’s pre-infusion Jim, but not as we know it”.
My understanding (relative novice = feel free to correct me) of pre-infusion is that a relatively lower pressure (say 2 - 4 bar) is held constant for a period of time (typically 5 seonds although Rao will do up to 39 seconds for his “blooming” light roast pours) to soak the puck before ramping up to say 9 bars for the bulk of the extraction.
By the look of the above graph, the ramp up of pressure is starting lower and moving to 9 bars so it is going to have a similar effect.
You clearly like the result of the 9barista so I guess your quest to know more about pre-infusion is motivated by the same thing that keeps many of exploring further down the rabbit hole: I wonder if this could be even better?
