Psyd wrote:I dunno, it's possible that the nine(ish) atmospheres accumulating in that headspace might make it teenie bit different from that curved watering can spout and bowl.

Man, no one ever laughs at my jokes. Why do I even bother being bombastic? But seriously, 9 atm just strengthens my point, you know.

Psyd wrote:Who invented the curved tamp, and why did they do it?

It probably doesn't matter? People do crazy and misguided things all the time. Just look at me last weekend.

RapidCoffee wrote:1. Depends on basket/dose/dispersion block...

Yes, exactly. I was asking these rhetorical questions to make the point that there many dependent variables at play that we cannot simply ascribe to curved versus flat piston. Too many other variables change simultaneously.

RapidCoffee wrote:4. Some folks claim that the puck compresses under pressure, and only expands when the pump is turned off. Sounds reasonable, but we may not know for sure until the mythical plexiglass portafilter video resurfaces.

Expansion or contraction will depend on the changes in compressibility of the dry puck versus the wet puck. The wet puck might very well either expand or contract at 9 bar pressure, and certainly expands at the end of extraction without question. However, does it really matter for any practical reasons?

RapidCoffee wrote:Water is not very compressible. If the headspace fills with water (which seems likely), then the brew pressure should be transmitted evenly across the surface of the puck, regardless of shower screen geometry. That's why I have a hard time believing that the curvature of the shower screen has any impact on the optimal tamper shape.

Absolutely! I think the point I was trying to make was that curvature of the screen and tamper each DO have an effect, but the two are not linked. Sort of like saying: "I use my black grinder for dark roasted beans."

drdna wrote:Sort of like saying: "I use my black grinder for dark roasted beans."

Awesome! So I'm not the only one!

I have many flats pistons and a c-flat piston. I've found over time the c-flat gets a lot more time in my hands than the others. Reason why? I think it looks cooler. I.E. It doesn't make a difference.

Plus I love how brass feels when you're compacting that puck.

drdna wrote:It probably doesn't matter?

It probably does.
Either it was motivated by some sort of research, and it has a reason, and knowing the reason might help us apply the curvature in the manner that the designer discovered that it would change the shot; or the perhaps the research and reasoning was flawed, in which case it can be dismissed.

Or, it could have been pure hype and marketing, in which case we can put it in the same category as racing stripes and fins.

Sure, they look great, but they really don't do anything.

Knowing how it came about will have a great impact on understanding how it will (should) be used.