Speculations on espresso body and mouthfeel - Page 6

#51: Post by **jpender** » September 28th, 2019, 10:56 am

AssafL wrote:I don't even know where to start. In the case of hypothesis you are confusing mathematical proof with the hypothesis in the scientific method. No relation between the two. Is the drift equation for excess electrons okay for a semi conductor? Or do you add corrections for newer subatomic corrections? Depends on your need. But the current hypothesis will never be proven and at some point add corrections. Unlike math.

Now don't be mean to me. I'm not talking about math. And what is the "drift equation for excess electrons" anyway? Are you talking about drift velocity? It doesn't really matter, I'm just curious.

The point is that (whatever you are referring to specifically) there is a theory with an equation or equations. You can make quantitative predictions. You can measure the results experimentally and compare them to what the theory predicts.

And what do you have?

AssafL wrote:As for "compress" all I can say is yes it compresses. If you ever used a tamper at 30# you'd see the initial pile is severely compressed by tamp end. At 9 bar and a 58mm basket you are at 400#. Why would it not compress more?

That's it. You just say "it compresses". You can't say how much. You can't say how. You can't model why it "seals" the flow. You can't make quantitative predictions. It's just an idea of yours. It might be right but you're presenting it as if it's established fact when that's just a little bit premature.

This is a thread about speculation. Why not cast it as a speculation instead of a certainty?

#52: Post by **AssafL** » September 28th, 2019, 11:29 am

The hypothesis served me well until now and hence is either correct or a very good approximation of whatever is happening. I don't treat it as fact but as a hypothesis.

I also treated fingering flows as fact/hypothesis and it took Dave a single sentence to refute it.

Fines migration was treated as a hypothesis but doesn't fit the evidence. So mostly refuted.

I actually like being wrong. When proven wrong I usually learn something. So please refute it! (This is a hobby for me so being wrong bears no cost with it).

Maybe someone with a transparent basket can try to do a PI less pull using fine grinds and see what happens. I don't have one...

#53: Post by **jpender** » September 29th, 2019, 1:29 pm

The reason I'm skeptical of your notion of puck density change is because while air acts like a spring a bed of ground coffee does not. When you remove the tamper the coffee doesn't spring back up. There is some modulus of elasticity for roasted ground coffee but when you tamp it you're not compressing the cellulose. You're packing the grounds into a more efficient ordering. Perhaps there is some fracturing as well. So when the 9 bar gets applied I suspect it will be more of the same sort of irreversible compression, and to a much lesser degree since the coffee has already been compressed. A spring would react linearly to the applied force and be reversible.

I'll offer an alternative although not entirely dissimilar hypothesis. Perhaps the dry puck does not actually compress significantly, it just locks together akin to holding a lid down tight over the top of a container to keep liquid from escaping. That would be fully reversible without any real change in density.

I think it fits with what you observe just as well. And is equally unsupported by any direct evidence.

My hunch is that the hygroscopic hydrophobic nature of coffee also plays a role somehow. That once wetted it doesn't matter as much if it were pressed upon hard. Just speculating though.

#54: Post by **AssafL** » September 29th, 2019, 3:49 pm

Reality is probably in between. If it were a "crushed" sealing layer it wouldn't be reversible.

The again it probably doesn't spring back 100% of the way - as the tamper shows.

A hypothesis would be that only the air fully trapped in closed particles rebounds. But that wouldn't create the pathways for extraction to be reestablished (spaces between grinds).

What I still maintain is that given a ratio of dry grinds to air - when pressed down by 400 pound force (135 PSI) the volume of air decreases (ideal gas law) and thus the density (grinds to air) increases.

I suggest we take this either to a separate thread and/or rekindle Jake's PI thread - where these theories were originally conceived.