Jake_G wrote:I'll bow out of here for now unless I think of something super decent-related.

I have read some of your ramble thread, but won't claim to have fully processed it. But it does feed into some Decent thoughts I have had over the last few months, and I welcome any thoughts you have in response.

I agree that it likely is a good idea for your puck to be full saturated before pressure is applied. And I think low flow preinfusion also minimizes the likelihood of disturbance to the puck. That said, I suspect there is a point at which flow is so low (and preinfusion so slow) that it begins to have a negative effect on the espresso. I would posit that the highest flow for preinfusion that maintains the total amount of water used for preinfusion is a good target. Maximizing the total water during preinfusion implies one has fully saturated the puck, and if one is able to do so at a higher flow rate, I would take that as a good indication that the flow rate is not unduly affecting the puck's integrity.

So, although I don't (quite yet) have a Decent machine to test this on yet, I would posit that when dialing in a coffee/dose it might make sense first to set the flow rate for preinfusion very, very low with an exit based on increased pressure. This would allow a good estimate of how much water it takes to fully saturate the puck. Then, adjust the flow rate during preinfusion until the total water used during infusion drops.

Thereafter, if you are using a similar coffee (e.g., same beans, similar freshness, but from a different roast batch), one could assume that the flow rate previously determined is a good place to start, with perhaps some adjustments based on total water used for preinfusion, and/or for freshness of the beans.

I'm curious to test how well this works in practice, and to see what flow rates this methodology suggests are appropriate for preinfusion. And, of course, to taste the results.

Jake_G wrote:I find it interesting that preinfusion flow rates seem to be 4ml/sec on the profiles I've seen this far. Damien commented that this higher flow rate was due to the larger headspace on the decent machines. I suppose I would be tempted to use a basket and dose combo that resulted in a typical headspace, but perhaps that would require a dosing funnel and acrobatic up-dosing to achieve?

As it so happens, I'm getting a smaller basket with my machine. I already have an 18g Decent basket, and am getting a 15g basket with my DE1+. So I will have some ability to test the effect of headspace. It's not a single variable change, though - I'm told the holes on the 15g basket are smaller than on the 18g basket.

roastini wrote:I would posit that the highest flow for preinfusion that maintains the total amount of water used for preinfusion is a good target. Maximizing the total water during preinfusion implies one has fully saturated the puck....

Hi Michael, I'm seeking to follow you here and I'm wondering if you could say the same thing only differently? Happy Pulls with your Decent!

Tonefish wrote:Hi Michael, I'm seeking to follow you hear and I'm wondering if you could say the same thing only differently? Happy Pulls with your Decent!

Sure.

First, there is some maximum amount of water the puck will hold without dripping, just as there is a maximum amount of water that a dry sponge will hold. To find this amount, we drip water in slowly. This allows the water to fill the puck my capillary action. So we do this to determine the maximum preinfusion volume. If you get drips out of your puck BEFORE preinfusing with this volume, you did not fully saturate the puck.

Second, what is the best period of time in which to complete preinfusion? One possibility is that you want it to be as long as possible. This seems highly unlikely, as you will extract from different parts of the puck at wildly different levels, because parts of the puck will wet earlier and thus start extracting earlier.

It seems more likely to me that you want to saturate the puck as rapidly as you can, while ensuring that you do, in fact, fully saturate it.

So you could just pump water as fast as possible. But doing that likely will result in filling the headroom long before the puck is full saturated. Pressure will rise, and likely you will disturb the uniformity of the puck, leading to a suboptimal shot.

But through experimentation, one should be able to determine a maximum preinfusion flow rate that fully saturates the puck before the puck drips.

My theory is that this is the magic preinfusion rate for a given coffee/grind/dose - the quickest way to get the ideal saturated puck.

It may be that this doesn't exist - that as the preinfusion rate slows, the saturation volume asymptotically approaches a maximum, meaning that any increase in flow rate reduces the water absorbed before dripping begins. Or it could be that it does exist, but still requires an absurdly slow preinfusion rate.

If either of those are true, the ideal rate might be a fuzzier concept.

And determining which of these is true experimentally is hard, because slight difference in distribution or tamp could affect the experimental results.

But it seems worth exploring.

Jake_G wrote:Damien commented that this higher flow rate was due to the larger headspace on the decent machines. I suppose I would be tempted to use a basket and dose combo that resulted in a typical headspace, but perhaps that would require a dosing funnel and acrobatic up-dosing to achieve?

There is air above the puck at the beginning, that needs to be compressed by water, so bigger the headspace more water needed for that I think ...

roastini wrote: First, there is some.maximum amount of water the puck will hold without dripping, ...
...Second, what is the best period of time in which complete to preinfusion? ...
...But it seems worth exploring.

Got it. Thanks Michael!

Jake_G wrote:I think the pressure ramp is a good discerning point to end the preinfusion, but the real indicator of a saturated puck (or I suppose the end of preinfusion) is wetting the basket. It will be interesting to see if there is congruence between these two events, and if so, what pressure rise signifies a filly wetted puck. Obviously, this depends on the puck integrity and the flow rate during preinfusion, but I suppose the real question is "does wetting occur at peak pressure, after peak pressure, or at some consistent fraction thereof, or does it appear to be wholly unrelated?". And does knowing any of this translate to better results in the cup?
- Jake

I've done a little investigating of this question. Unfortunately right now it is not trivial because it is hard to watch the charts and the basket at the same time. The only way I've found is to make a movie from an angle that captures the charts on the top of the screen, and the basket in the mirror at the bottom of the backsplash. I've attached a final shot chart from the one movie I made, and marked on it when I saw the first drops appearing. As you can see, wetting occurred after pressure rise began (at about 2 bar), but a second or so before the end of preinfusion was triggered at 4 bar (the vertical line). [This was a pressure profile rising to 8.4 bar, holding 8 seconds, then declining, as shown by the dotted green line. Ignore the pale colored lines. The weird pressure profile number in the lower right is one of those tedious bugs that is now corrected]

I discussed making this process easier with John Buckman, and suggested having the machine optionally make beep sound at profile transitions. This way you could video the basket directly, and sync the chart to the video later. I suspect some variant of this will be incorporated in a future software update.