The sequence in the title is something some of us owners of the Decent DE1 have been playing with lately. Scott Rao describes one such recipe in his blog here:

https://www.scottrao.com/blog/2018/7/18 ... on-the-de1

In short:

1. Preinfuse 4.0mL/sec @ 98°C for 25 seconds or until pressure reaches 4.0 bar
2. Pause (0.0mL/sec flow) for 30 sec (set water target temp to 92°C from here on)
3. Ramp pressure using 2.2mL/sec flow for 5 seconds, smooth transition
4. Hold flow at 2.2mL/sec until target weight reached on scale

Another Decent owner Michael K has a different approach:

1. fill headspace: 90°C, 3 mL/s, 20 seconds, but exit if pressure is over 1.3 bar.
2. bloom: 89°C, 1.0 bar, 30 sec.
3. rise: 88°C, smooth transition to 1.5 mL/s flow in 3 seconds, but exit if pressure exceeds 9.5 bar.
4. flow extraction: 88°C, 1.5 mL/s flow for 60 seconds, but exit if pressure exceeds 9.5 bar. Typically this is the final stage.
5. cap pressure if necessary: 88°C, 9.5 bar, 2 seconds.
6. pressure until decline: 88°C, 9.5 bar, 60 seconds, exit if flow over 1.5 mL/s.
7. revert to flow if pressure cap is reached: 88°C, 1.5 mL/s, 60 seconds

This fixes some of the issues I've also found in Rao's recipe which is that the flow rate target in the latter stages causes pressure to vary wildly unless everything is perfect. However, it differs from Rao's recipe in that it exits preinfusion at low pressure, and holds 1 bar of pressure during the pause. Rao's recipe has a pressure curve that looks like a declining slope during the pause, because even though no water is being pushed it had already ramped up to 4 bar and the pressure slowly decreases through the puck over time.

My personal approach is some sort of hybrid with Rao's preinfusion/pause and a declining pressure profile from 8 bar to 4 bar afterwards.

Has anyone here done any analysis on a pause/bloom stage during espresso extraction? Unfortunately my skills are only average and I don't own a refractometer, and I don't really drink enough coffee to justify pulling 10 or 50 shots in a row like they did here: https://compoundcoffee.com/experiments/ ... n-espresso. However I'd be willing to entertain this forum's suggestions for things to try.

I don't have the DE1 but it sounds like you are on the right track!

That coffeecompound link (Thanks for posting that!) is yet another preinfusion study where they've controlled the wrong variables to hide the benefits of preinfusion. They let the time vary instead of adjusting the grind to maximize the extraction benefits of the preinfusion and ended up with extraction yields you would expect when not optimizing for the preinfusion approaches. At least they admitted that though, and that taste should play a role too. And that was two years ago ... good for them for giving a go at that!

I like how Rao at least indicates acknowledges the grind contribution instead of only paying attention to flow. That was a good check.

Sometimes I think about the Decent machine owners being able to work togehter for massive studies with each machine collecting a datapoint or two to add to the collective, but the environment variables may foul that dream.

Anyhow, have fun with your DE1 and keep up the exploration!!

There are a few other threads that have been exploring the same thing (as well as the DE1 threads themselves). I've been doing some experimenting myself but as I'm still breaking in my grinder I can't really say what methods work best yet (vs what's just my grinder breaking in). I think the general concept is sound though (soaking the entire puck, letting it sit for a while and expand a tiny bit, and then proceeding with the pour). It ensure all the grounds are at peak solubility before the pour as well as possibly fixing any tiny imperfections in the puck itself thanks to the swelling.

Extending E61 Preinfusion

My long and rambling path to preinfusion/pressure profiling

Thanks for the hints there on those threads. It seems to me that there's just an enormous amount of new variables to consider. After catching up on those threads It makes sense to me (and follows Rao's recipe) that exiting preinfusion at 3+ bar is necessary to saturate the puck, and that 30 seconds is a reasonable dwell time for blooming. However I think we still need some more data...

One thing that's clear on the DE1 which might not be as obvious in a thought experiment is that once the system of portafilter, puck and water reaches measurable back pressure, if the pump is turned off, it will still stay at that pressure until it is released through the puck slowly. It looks like a steep slope on the graph. On the other side, of course, coffee is being emitted into the cup. I get between 0.7g and 2.0g during the bloom. I'm curious if that poses an additional consideration in the tradeoff between full saturation at higher pressure vs partial saturation at low pressure. Are these first drops essential to the balance of the finished drink, or should they be minimized or even discarded?

Another possible variable is, perhaps 3+ bar should be sustained for some time before being allowed to release, and if so, how long?

Yeah that's something I've been playing with. I preinfuse at under 3 BAR (I've been playing around with 2/3 BAR, haven't decided if there's much difference yet and haven't tried values around 1 BAR yet) and as soon as I see drips accumulating on the bottom of the portafilter I stop the water flow and bleed as much pressure as is needed to prevent dripping (I'm not sure what BAR the chamber has at that point as the gauge on my ECM only tells you the pressure above the head).

I haven't seen anyone make a DE1 profile where they pull back the pressure on the head after preinfusion for the bloom, but maybe that's why I see some of their profiles using super low BAR values for preinfusion (so that they can hold that pressure during the bloom without having to bleed pressure like I've been doing)? Maybe I need to give low pressure preinfusion a try (although I've read that it can cause dry spots in the puck).