DrRoadrash wrote:If distribution is even I think tamp pressure has little to no effect, if it is uneven I think higher tamp pressure somewhat "corrects" the distribution and slows the extraction.
I find that slowly increasing my tamping pressure over 15 seconds or so seems to help even out distribution. When you think about it, all those tiny particles can shift around to fill voids in the puck, unless & until they're mechanically locked in place against each other. Pinch a small pumpkin seed quickly between your fingers and it will be held there. Pinch it slowly and it will "squirt" from between them. So gradually increasing tamping pressure might logically help break up and shift clusters of ground coffee bits from denser spots to less dense unless they're already held firmly together & cannot physically break up and move. I suspect this is the major benefit of nutation and is of no value if (as you observe) distribution is already even.
Think of a basket full of particulate matter as a fluid rather than a solid, and the above makes more sense. We use fluid mechanics and principles to study blood flow, and blood is full of particles (red and white blood cells, immune complexes, platelets etc etc). Fluid is incompressible, as is a solid particle of coffee. So dense pockets of ground coffee within the puck will transmit tamping pressure if they're already locked together but shift & break up to relieve it if the clustered particles are still moveable against each other.