StefanoB wrote:Thank you very much! I like this reasoning!

What I would like to rationalize, is the effect on taste. If I try to slow down the shot, is to extract more nice flavors, and at the same time try no to extract the unpleasant flavors such as bitterness.

I guess by grinding finer I risk extracting bitterness, while playing with tamp pressure only probably is safer to avoid that? Would you agree?...

Another question: I have tried nutation without seeing obvious differences than with direct tamp, but my nutation technique is probably poor. With a good nutation tamp which changes would you expect to see in the cup?

Nutating tamps give you too little of results for something that needs to be done quite well in order to be effective and generally it is not recommended especially when you haven't developed this skill set. If grinding finer gives you the unpleasant overextracted tastes but you still want to extract more I would work more on other pre-tamp prep of the puck like WDT to prevent things like excess chanelling.

You can also try to added an aeropress filter at the bottom of the PF basket (under the puck) as well as at the top of the basket (on top of the puck). The bottom filter helps to prevent fines clogging up the basket holes and the top filter helps to prevent early erosion of the puck. Both help to create more efficient flow and typically will speed up the shot but it's more like a bandaid. What this allows however is for you to grind finer and thus extract more before overextracted tastes come in. Essentially you raise the extraction ceiling because the flow is more even. This usually works quite well and there is a noticable difference right away but because you're running it through a paper filter the shots tends to be thinner even though they are higher extraction and TDS so the mouthfeel seems counter intuitive to the extraction.

Other things you may want to do is grind finer and dose down or just let the shot run a little bit longer. The dosing down while going finer may get that sort of sweet spot you're after, extraction will be higher because the coffee is finer but the TDS may be about the same because there is less coffee however it really depends on the yeild. Running the shot longer will expose the coffee to more brew water and will extract more. The trade off of course is higher yields which could would be more diluted. It would also have an effect of higher extraction but less TDS but again it could be the sweet spot you're after.

Grind size to me is just getting the shot in a window of a good shot. Once it's there then start playing with other things to make it a better shot. If you have any ability to pre-infuse then this would be something you'll want to experiment with to get the most out of the shot.

Thank you Damian for this most valuable post!