HBchris wrote:I could be off but isnt flour much finer and/or very different textured compared to coffee. I am just thinking its rather powedery / "cakey", i couldnt imagine taping causing anything to get through a layer of flour. But i am not sure if this is flour specific, maybe sugar would be better comparable for demonstration? Or if there is a way to dye a portion of grounds a certain color. Just speculating.

+1

HBchris wrote:... maybe sugar would be better comparable for demonstration?

Uh huh. And if I had used sugar, I'm sure someone would have suggested using flour. If you think sugar and coffee grinds will produce a different result, why don't you try it?

Obviously the best test would be Chris (aecletec)'s idea of using different roast levels of coffee.

LBIespresso wrote:This got me wondering, what is the impact of tamp pressure on espresso? Like how would a shot, all other things being equal, taste differently with a heavy tamp vs a light tamp?

That's a great question that almost needs its own thread, hah! Espresso beds are packed granular bodies with a power rule particle size distribution and the flow of water moves through it very similarly to the way it moves through underground aquifers and has been modeled many times. In short, the harder you press when you tamp, the more you are compressing the coffee bed from the center slice outwards which is not exactly intuitive. Imagine it this way: You have a bunch of empty cardboard boxes in a line on the floor, and you and a friend are pushing from both ends. Now imagine the very middle boxes crush first, then the ones next to them and so on outwards. That's generally what's happening in the espresso bed, so if the middle is more densely packed than other areas, the water will avoid it leaving behind flavor and body that you could have had.

Also, tamping harder slows the shot down so tamping lighter speeds it up (duh). If you tamp lighter, you can actually grind finer and expose more surface area to the water meaning you get more flavor and body with the same ratio. Here's an example:

Recipe: 20g dose, 40g yield, 30 seconds
Shot 1 Tamping super hard, coarser grind: Medium body, medium sweetness
Shot 2 Tamping lightly, finer grind: full body, rich sweetness

So to answer your question, shots that have been tamped lighter and ground finer will have more flavor and body. Just depends on what you're going for I guess!

Maybe I'm missing something here, but it's my feeling that looking at layers of different powdered substances in a glass is completely irrelevant to looking at the distribution of ground espresso (one single thing) in a portafilter basket. We're not trying to see how well sugar and chocolate powder mix, we're looking at the density distribution of ground coffee. And unless your grinder is spitting out very stratified layers of boulders followed by fines and back and forth (spoiler alert: it isn't) looking at these layers of white and brown is useless. Of course using a whisk is going to make a uniform mixture of two colors.

At the end of the day (or first thing in the morning, hah!) all we want is a method to distribute the density of the ground coffee uniformly before we tamp. Why? So the water moves through the coffee uniformly grabbing all the tasty things we want. WDT works. Tapping also works. Palm/finger grooming alone not as well. The only real evidence we have of uniform extraction/distribution is observing how the basket "lights up" on a bottomless portafilter. Try some different things and see for yourself!

CorvusDoug wrote: Also, tamping harder slows the shot down so tamping lighter speeds it up (duh).

Oodles of controlled testing shows that this isn't necessarily the case.
Taken seriously, arguments akin to "models aren't coffee" would negate just about everything we think we know about coffee because it's either modelled on computer or not the way brew at home or in café.

CorvusDoug wrote:Also, tamping harder slows the shot down so tamping lighter speeds it up (duh).

This is a misleading statement. I have consistently found that tamp pressure over 5 pounds has no impact on flow rate. No tamp (or just weight of tamper) produces gushers unless the grind is made finer, and (at least for me) results in less consistent pours. This is easy enough to test; all you need is a scale and a timer. My results confirm studies performed by Socratic, discussed at length in this thread.

CorvusDoug wrote:So to answer your question, shots that have been tamped lighter and ground finer will have more flavor and body.

Is this speculation, or did you actually confirm this by experiment? If so, please share your protocol and results.

I'm aware of that experiment by Socratic, and it makes no mention of distribution method or lack thereof which is in my opinion and experience one of the most crucial parts of espresso preparation. Also, the information that is glaringly missing from the study is a chart showing the relationship between tamping pressure and time of shot. Their time range goes from 32 to 46 seconds on only one chart comparing time with beverage weight. Another observation about the study that differs from my own experience in that our Linea is set to 6 bar and Synesso mvp has pre-infusion/ramp down rather than Socratic's constant 9 bar setup. Additionally, I couldn't find any information on the "MC Euro Classic Espresso Blend" used in the experiment but I suspect it's a bit different than the lighter roasted stuff I'm used to working with for whatever that's worth.

I have not done this specific experiment but I would set it up this way: In short I would compare tamping force with grind setting needed to achieve the same recipe (ex: 20g, 40g, in 30 seconds) and read the TDS of each shot.

It's not only Socratic, many others have replicated the experiment.
Anyway, here's dyed coffee grounds showing the same lack of ground mixing.