Looking for a Simple Measure of Preinfusion - Page 8

Beginner and pro baristas share tips and tricks for making espresso.
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TomC
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#71: Post by TomC »

I haven't seen dosing mentioned too much in this thread. It's a fascinating discussion nonetheless. I'd imagine whatever device you're using to extract from, having a coffee "cake" right up under the dispersion screen would drastically alter your measurements. Not having a void above the surface of the coffee prior to saturation might change everything you're putting under the microscope.

I'm having the most fun studying the DE1 Pro, and aiming to have fully filled baskets and less headspace.
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AssafL
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#72: Post by AssafL »

PI is a function of the puck. Not what we do.

I have a more accurate flow meter (a digmeesa courtesy of member piezo) - and it is uncanny how stable PI volume is. For an 18g dose PI volume is always 28-30ml until first drops.

Grind, coffee, dose, roast: all these do is to change how pressure gets effected (my pump being volumetric) - slowing PI means more time to soak and less pressure build up at the end.

If everyone had a digmesa I'd say the best way to tell PI is over is volumetric. The Gicar in the GS3 wasn't very linear at low flows and therefore wouldn't work for this.

Still, as a post drip consistent way to tell PI is sure to be over - the 5gr method is nice. Obviously it would be unlikely to coincide with the real PI being over and would add a few seconds to PI (which ought not be there).

(Can't post graphs as my ESP 8266 is misbehaving).
Scraping away (slowly) at the tyranny of biases and dogma.

mike guy

#73: Post by mike guy »

another_jim wrote:Comparing the instantaneous pressure and flow rates on Dick's first graph of the shot with the pump on constant power: if you replot them flow versus pressure without a time axis, it shows the classic pump curve of decreased pressure with increased flow. The third graph shows that to maintain flow with the less resistant puck, you have to drop the pressure more via controls than it would drop naturally. My point is that you shouldn't expect constant pressure in non-profiled shots.

The graphs of flow rates as the puck saturates, before seeing or weighing a flow; how good are these? I'm not doubting that the flow metering is accurate; I'm wondering how many nooks and crannies in the water delivery are filling up along with the puck.

For instance, the head space above the puck. Imagine the puck is impermeable below 3 bar, and totally permeable above 3 bar. Then the head space would fill first, and the puck would fill second. If the puck is permeable at every pressure except for the lowest layer, it would fill first, and then the head space would fill second.

When you do pour over, you see the coffee absorbing water at a certain rate, when the pour rate is higher, the water pools over the coffee, if it is lower, the water soaks in. If the puck is like that, and you have gicleurs and and cavities in the water path, what rate at which the puck gets wet may not very precisely parallel the flow rate measured at the pump.
I think this is a very good observation. After Scott Rao posted about how he was getting great extractions with a "bloom", I repeated the line pressure preinfusion experiment post that declared that the whole puck didn't get wet until above 3 bar (if I recall correctly). I found that to not be accurate, and it had more to do with time opposed to pressure. IE at 2 bar if I pulled the portafilter and inspected the puck immediately after seeing the bottom of the basket covered in coffee, there were indeed dry spots in the middle of the puck. If however, I instead shut the flow off when only the edges of the basket showed extraction, and then let the coffee sit for 30 seconds and bloom, the puck was fully saturated. Even though flow was off, the pressurized environment of the basket and expansion from co2 being released from the coffee, completed forcing water through the entire puck.

I completed the experiment at 1 and 3 bar line pressure and decided that pressure made almost no difference and time was everything. My general conclusion was that flow can stop, but there is still lots of water and co2 pressure that will create another type of expansive flow that will keep water moving.

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another_jim (original poster)
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#74: Post by another_jim (original poster) »

mike guy wrote: ... I completed the experiment at 1 and 3 bar line pressure and decided that pressure made almost no difference and time was everything. My general conclusion was that flow can stop, but there is still lots of water and co2 pressure that will create another type of expansive flow that will keep water moving.
Interesting. So, a recipe like "get the water into the puck by filling the head space and waiting 30 seconds for it to soak, then get the brew out by turning the pump back on, and filling the cup" might be a general recipe for high, even extractions.

But I'm wondering how machine and grind dependent this all is: Ken Fox did a similar experiment with Cimbali Juniors many yeears ago, and saw complete soaking in 6 seconds with a 3 bar preinfusion. This was back in the high dose, coarse grind days. Could it be that the current use of fine grinds has such a dramatic effect on puck soaking times?
Jim Schulman

mike guy

#75: Post by mike guy »

another_jim wrote:Interesting. So, a recipe like "get the water into the puck by filling the head space and waiting 30 seconds for it to soak, then get the brew out by turning the pump back on, and filling the cup" might be a general recipe for high, even extractions.
Yes, that's the general strategy. I find it quite useful for light roasts that are hard to extract. I grind finer, lower the brew pressure, do a line preinfuse / bloom for 30 seconds, and then start the pump. I've been able to get some really nice extractions on lighter roasts that I previously only enjoyed as pour over. As with everything, the recipe varies a lot and what works for one coffee will easily make another one worse. The bloom is not a panacea, at least with my equipment.

For example I find that this does not work well for medium traditional espressos and they will trade their sweetness for bitterness. But as you point out, maybe the direction to go on those is coarse grinds and a more coffee brew style.

I'm using an e61, so my options for doing this kind of thing are very limited compared to those with a full pressure and flow control.

The link you mentioned was the experiment was the exact one that I referenced in my post (could not find it earlier) where my findings where different. My strategy was a bit different though. Instead of letting the line pressure just go and then turning on the pump, I cease the line pressure, but do not trigger the 3 way valve so the group head and basket are also under pressure. I can try and get a video of this happening, but you can tell some kind of expansive flow is still happening even with the line pressure off. In that you can observe coffee forming at the outer edges of the basket, but by the time the 30 seconds are up, the entire bottom of the basket shows coffee. Not every e61 can do this I believe, there is an extra engagement point on the p700 / synchronika lever design that makes it possible to maintain valve pressure.

Here is the article that prompted me to try adding a bloom to certain roasts:
https://www.scottrao.com/blog/2018/7/18 ... on-the-de1

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Peppersass
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#76: Post by Peppersass »

Just based on my GS/3 experience, there may be too much variation between machines, and/or too many limitations, for profiling recipes to be widely applicable.

For example, the stock GS/3 AV can't do a "soak" after preinfusion if it's plumbed in because water will continue to flow unless you close the 3-way. Then, if there's any pressure in the basket, which would almost certainly be the case, the pressure will be released, drawing some of the water and puck up and out the exhaust. The puck usually breaks up when this happens, even if the pressure is relatively low.

My modified GS/3 has the same limitation because it's plumbed in. I could get around it by manually turning off the input water line, though it would be awkward because it's in the cabinet under the machine. Sort of a tricky manual maneuver to do that just as preinfusion ends, too. I guess I could continue to preinfuse at 1.5-2.0 BAR for another XX seconds, which is close to a soak because it doesn't push much water through the puck, but it's not the same as a true soak.

A soak may be possible with the reservoir option and volumetric buttons, but it's been 9 years since I played with that and I can't recall if the motor is turned of with the 3-way left open.

The MP doesn't have a 3-way, per se, but I think the group valve incorporates a similar exhaust function. If so, it would have similar constraints when plumbed in.

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AssafL
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#77: Post by AssafL »

The GS/3 AV (at least the software versions I know of) links the motor to the 3-way. Hence no line level PI built in. Which is a shame as it is a handicap of the software.

I was told it was because most AV are not plumbed in.

I can do a soak of sorts by closing the FLB (flow Limit bypass), and closing the needle valve.

Metering valves are not designed for on-off (the needle binds in the orifice destroying the valve), but one can easily go under 1ml/Sec. As low as 0.5ml/ Sec at which point it nearly stalls.

Personally, I don't know If soak is at best a literal soak or whether some (minimal) pressure is better to maintain puck integrity.

As an example, letting go of the Cafelat Robot arms (the gravitational equivalent of a soak, doesn't seem to work well. But I don't have enough experience to be confident it never works. Maybe a finer grind?

I think I stated earlier - PI is a function of the puck. You can PI mid pull. I've tried it and it is somewhat silly. But if you grind fine, ramp up pressure quickly (brick wall it), and get it to seal, you can pull back slowly until pressure decreases to PI level pressure, wait for PI to finish and continue the pull normally.

In other words - a puck sans PI is not yet a puck. It is more like pressure only sintered pack of coffee powder. I am reasonably confident in my assertion to all those who pretend to dislike PI, that indeed (if they have flow) their puck had indeed completed PI. Even if it was a coarse grind 2 second gicleur PI. Or a lever detent 1 second pause. Or the second it took the faucet to open. Or a chamber somewhere filled up. Get over it. You PI'd. Or you'd have no flow.
Scraping away (slowly) at the tyranny of biases and dogma.

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RapidCoffee
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#78: Post by RapidCoffee »

AssafL wrote:PI is a function of the puck... a puck sans PI is not yet a puck.
Not sure I agree with your provocative statements, but I think we're on the same page. Pumps cannot ramp up pressure instantaneously. So every espresso extraction has a "preinfusion" stage, in which the puck gets infused/saturated. Only then does pressure build to 9 bar (or whatever).

Some machines offer control over this step, and some do not. My Spaziale S1V1 has no preinfusion control, and ramps up pressure very rapidly, largely as a function of the high-water debit rotary pump. Nonetheless, there is a preinfusion step.

The preinfusion step is critically important in the overall extraction. This was noted over a decade ago by Andy Schecter:
I've been saying for years that it's the pressure/volume relationship in the first few seconds of the extraction that is most critical in determining flow rate.
A greater understanding and manipulation of the preinfusion stage will undoubtedly result in better extractions.
John

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AssafL
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#79: Post by AssafL »

RapidCoffee wrote:Not sure I agree with your provocative statements, but I think we're on the same page. Pumps cannot ramp up pressure instantaneously. So every espresso extraction has a "preinfusion" stage, in which the puck gets infused/saturated. Only then does pressure build to 9 bar (or whatever).

Some machines offer control over this step, and some do not. My Spaziale S1V1 has no preinfusion control, and ramps up pressure very rapidly, largely as a function of the high-water debit rotary pump. Nonetheless, there is a preinfusion step.
So there are unique puck parameters (dose, grind, roast, etc.) for which the Speziale's PI setuyp works.

Other pucks would need a different machine. It is the puck that determines what PI would work for it (if at all).

Modifiable PI allows various pucks to to used on the same machine.
The preinfusion step is critically important in the overall extraction. This was noted over a decade ago by Andy Schecter:


A greater understanding and manipulation of the preinfusion stage will undoubtedly result in better extractions.
Yup - not invented here. But new and inexpensive profiling allows one to put into practice what we thought we knew.
Scraping away (slowly) at the tyranny of biases and dogma.

Bret

#80: Post by Bret »

RapidCoffee wrote:....but I think we're on the same page. Pumps cannot ramp up pressure instantaneously. So every espresso extraction has a "preinfusion" stage, in which the puck gets infused/saturated. Only then does pressure build to 9 bar (or whatever).
I'm not sure I agree with this: I am using medium dark roasts, grinding very fine, and doing long extractions that go to 9.5b at the start, and it is several seconds at high pressure before drips are seen. Oftentimes, once the thick syrupy drips switch to flow (30-45 seconds later) then the pressure drops toward 9 bar. So I would say that with a fine enough grind, the PI pressure is 9+ bars