Adrianmsmith One thing I find strange whilst making decaf for my wife is, during preinfusion I see more flow and sooner (almost instant) than my normal beans.
Hmmm … I presume that your machine pre-fills the headspace pretty quickly and with pressure, particularly if there is little headspace between the top of the puck (or puckscreen) and the grouphead diffusion screen (your screen). Limited headspace is not a bad thing. I like a nice firm puck, even though with my basket and dose, my puck is abit soupy, which is ok but something that I will fix with a mod. But that may be the beginning of the cause of your early flow.
Subsequently I am curious as to whether your machine continues to apply pressure during the blooming phase of the pre-infusion or not. If it continues to apply pressure, you might see some early drips. Some profiles that I have used produced as much as 4g espresso during pre-infusion; I personally didn’t like that, but the profile I had then used (can’t recall which) actually suggested that I dial in to see those drips. But anyway if you are pre-infusing under pressure and the puck resistance at that stage cannot resist the pressure you will (by definition) get flow.
A couple of options: 1) will your machine allow you to ease up on the pressure during the blooming phase of the pre-infusion? 2) grind finer. Decaf does require a substantially finer grind than caf. I grind at 8.0 on my Niche Z. I don’t drink caf, but when I pour caf for guests I grind at atleast 13. I’d have to check my notes. I also grind without the FCD, so I an betting that I am getting more fines, which causes greater puck resistance and reduces flow (which with my flow target profile causes a significant increase in pressure).
Also: Are you using a high flow basket? Or even a normal IMS basket, which is still pretty high flow? I have switched to a moderate flow (EPHQ14) basket, that has no holes around the perimeter circumference and an overall lower hole count. I seem to be getting better results with my Full City roast decaf. You only need a higher flow with lighter roasts.
The bottom line: How is the taste? How do you like the: Body? Strength? Flavour Extraction? Flavour Length? Balance? If you don’t like the taste then you can go about applying potential corrections, one at a time. Decaf is not easy to get right. First and foremost one needs the right beans; so many roasters can’t get decaf right; a whole other topic.
But I have learned that flow rate is key. I aim for an initially fast headspace pre-fill (8 ml/sec) followed by 0 ml/sec for 4 seconds ramping up to 1.3 to 1.5 ml/sec and then declining to 1.0 ml/sec. Except that with my latest successful profile, I get a constant 1.0 ml/sec flow after the pre-infusion.
Fyi, my water flow more or less matches my weight flow, as my machine is calibrated that way. The “after the puck” water flow is estimated by the Decent based upon sensors and algorithms. The weight flow is based upon the weight measured by my Skale, which is transmitted back to the Decent.
Hope this helps.
