RapidCoffee wrote:Perhaps this is correct, but I'm not aware of any supporting evidence for puck density increase due to compressed air.

That is very easy to show. Grind until the no-PI stops the flow completely. Blast the puck with full pressure and wait a few seconds... If it stops - great!

Now - slowly down-ramp the pressure (not a 3-way "exhaust" - you want to keep the puck intact). Wait until pressure dissipates and now wait for it to PI.

Now ramp pressure again - flow will be as if the first "blocked" pour never occurred.

Air is a spring - and as long as air is in the puck you can play with it - and the process is reversible. Displacing the air with incompressible water is irreversible.

I disagree with the results from the Spaz being generalizable based on using much more extreme differences.

If you want a 100% or 90 % crema shot with absolutely superb mouthfeel, go extreme Seattle: grind coarse, dose high, and get a fast flowing shot that finishes in about 15 to 18 seconds of flow time. The crema is not noticeably different if I do this with a slow ramp up over 10 seconds, or a minimal dwell time of three seconds (i.e. with a no head space basket, and very fast water debit).

If I use a very fast flow with a very fine grind by dosing low, I get much less crema. If I go with a slow flow on a coarse grind by overstuffing a single basket, I also get less crema.

If you want a mousse-like espresso, coarse grind and fast flow is the way to go. I have no clue how this works, but I am fairly certain when people get a nice tongue and palte coating mouthfeel, they are getting a version of this kind of mousse-like crema

BTW: use a medium-dark roast for this experiment. It not going to go at all well with a light roast, when the mousse-like crema may be there, but the taste will be punishing.

another_jim wrote:I disagree with the results from the Spaz being generalizable based on using much more extreme differences.

If you want a 100% or 90 % crema shot with absolutely superb mouthfeel, go extreme Seattle: grind coarse, dose high, and get a fast flowing shot that finishes in about 15 to 18 seconds of flow time.
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If you want a mousse-like espresso, coarse grind and fast flow is the way to go.

I get this type of a shot under classic normale conditions, as described above: 15g dose, 1:2 brew ratio, extraction in ~35s. I am not grinding coarse, dosing high, or extracting a fast flowing shot.

It's possible the Spaz is an outlier... but why?

Typical shots run 45- 60 seconds & produce thick, creamy shots with excellent mouthfeel.

John, does the 45-60 seconds include your PI time?

Are the vibe pump Vivaldis also known for the heavier mouthfeel?

Excellent question, unfortunately I don't have the answer. But rotary vs. vibe pump comparisons of Cimbali and La Scala machines found no significant differences.

RapidCoffee wrote:I get this type of a shot under classic normale conditions, as described above: 15g dose, 1:2 brew ratio, extraction in ~35s. I am not grinding coarse, dosing high, or extracting a fast flowing shot.

It's possible the Spaz is an outlier... but why?

Maybe wave our hands and shout "chaos theory" and "non-equilibrium thermodynamics." At least the punters will nod sagely, pretending to understand.

The next step for me is to see if the changes are smooth or sudden. I'll grind finer and pull slower flowing shots step by step, and seeing what gives on tongue coating, mousse-like crema. The problem is that it's a qualitative judgement. So, in addition, I can pull the shots into glass, then take video not of the pour, but of how the crema looks and evolves over, say, one minute after the shot. Comparing the videos may shed some light.

mgwolf wrote:John, does the 45-60 seconds include your PI time?

Yes, the timer starts when the lever is engaged so the 12 second ramp to full pressure is included.

RapidCoffee wrote:I get this type of a shot under classic normale conditions, as described above: 15g dose, 1:2 brew ratio, extraction in ~35s. I am not grinding coarse, dosing high, or extracting a fast flowing shot.

It's possible the Spaz is an outlier... but why?

Are the group temperatures verified the same? Perhaps water temp is higher and maybe causing more CO2 to be released?

The vibe pump has less efficiency at high pressure compared to a rotary pump.

I believe you barely hit 3- 3.5 g/sec at 9 bar with a vibe pump, while with the rotary pump you hit more and in a shorter period. Faster flow and a more aggressive pumping means better emulsion in the puck creating that thick crema Jim is talking about.

Another thing after jumping with basket diameter (40-45-49-51-54-58mm I used in the last year) is that the smaller basket need lower dosage if you want to equivalent the grind (9-10g in a 40mm basket- Flair is equivalent to 18g in a 58mm basket). Putting 12-14g in the Flair basket means you are using a triple dose into the 58mm and this automatically asks for a coarse grind, that creates as Jim stated more body/crema.

Since I played at home with my full flow/pressure profile customizable machine, pulling at really low flow + 6-9 bar on a vibe can really affect the body (this with fine grind too). I always believed a lower flow will create less channeling in the puck, but in the end I didn't like the shots that much.

They key is to create a balance between mouthfeel and taste.