One thing I resonate with too is this:
I repeated the Jim Schulman-Ken Fox preinfusion experiments and got the same results of a shallow cone of dry coffee, of diameter about 50-60ish percent of the basket diameter and a height of 25-40% of the coffee height. The thing that amused me though, is that the once I hit the pump after preinfusion, the extraction begins is earnest from the cone botttom, as though the dry puck offered temporarily less resistance than the wetted part. This kind of makes sense though since preinfusion typically offers a finer grind for a given dose and coffee.AssafL wrote:If you don't let the PI continue to the end, the wet part of the puck (the top part of the puck), will act as a piston on the bottom part of the puck - the dry part. Being dry, the air (being compressible) will be pushed out and density will increase. Either the puck will be sealed, or water will be forced to find channels or, if the layer is thin enough, continue PI SLOWLY. Obviously SLOWLY depends on the size of the grinds. Boulders will be easier for the crushing water to permeate.