Pressure vs flow profiling

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Bluecold
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#1: Post by Bluecold »

DamianWarS wrote:if you're flow profiling than you're tracking the flow and the pressure will be dynamic but you're sitll going to have targets and a window of where you want the pressure to be so you have to adjust the grind/dose/etc... to ensure the pressue is in the right range you want it be while you flow profile. Since the DE tells you all of this stuff then you know if you've hit those targets and are able to adjust accordingly to tweak them.
I understand that when flow profiling, you have an expectation of pressure, but the flow difference between 11 and 9 bars is very slight. Flow profiling implies that you are interested in flowrate, therefore, a small difference in flow yields a small difference in taste. Which would make the difference between 9 and 11 bars not large enough to base adjustments on. At least not in itself.

Note: split from Can the DE1 simulate a cheap high pressure espresso machine by moderator.
LMWDP #232
"Though I Fly Through the Valley of Death I Shall Fear No Evil For I am at 80,000 Feet and Climbing."

Jeff

#2: Post by Jeff »

Surprisingly, a flow-controlled shot that peaked at 11 bar tastes notably different than one that peaked at 6-8 bar, both with the same flow rate. Many people consider the 11 bar shot to be inferior.

Davidm

#3: Post by Davidm » replying to Jeff »

Agree. I have had a DE1 for over two years and for the first six months predominately used flow profiling. My ideal shots were in the 6-8 bar range (dark roast maintaining 2 ml/s flow). Over 9 bar shots were definitely inferior.

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Bluecold
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#4: Post by Bluecold »

decent_espresso wrote:I agree. Maximum flow vs pressure is attained around 8.6 bar, which coincidentally is more-or-less what "9 bar" machines actually deliver.

Yes, those early Italian espresso inventors who figured this stuff out were quite clever.

At around 10.5 bar the coffee puck compresses quickly again, and increasing pressure beyond 10.5 bar results in rapidly diminishing flow. Hoffmann challenged me years ago on this, and I thought it was both counterintuitive and unlikely. I asked the Decent community to do the research, and it turns out I was wrong, and Hoffmann was right.

I haven't found a useful coffee reason to go beyond 10.5 bar, and in a future firmware version we'll enable flow profiles to define their own pressure ceiling.

-john
Doesn't this effect invalidate flow profiling as a concept? If you want a given flow, but you have two pressures to reach that flow, it's impossible to reproduce a shot if you only have flow information.
Jeff wrote:Surprisingly, a flow-controlled shot that peaked at 11 bar tastes notably different than one that peaked at 6-8 bar, both with the same flow rate. Many people consider the 11 bar shot to be inferior.
The graphs and discussion above would lead me to conclude that if you had left the pressure at 6 bar, you would perhaps have slightly less volume, but a much more similar shot.
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"Though I Fly Through the Valley of Death I Shall Fear No Evil For I am at 80,000 Feet and Climbing."

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decent_espresso
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#5: Post by decent_espresso »

Bluecold wrote:Doesn't this effect invalidate flow profiling as a concept? If you want a given flow, but you have two pressures to reach that flow, it's impossible to reproduce a shot if you only have flow information.
I find flow profiling absolutely essential during preinfusion, when there is no pressure on the puck.

Purely pressure-based espresso machines that describe preinfusion with terms like "3 bar" are giving you some sort of flow rate, dependent on the flow constrictor, and not 3 bar on the puck. The pressure that exists during preinfusion is only that of the flow constrictor on those machines. During preinfusion, the puck is not yet providing backpressure. Only by getting your scale out can you figure out what flow rate those machines are giving you.

I've found that pucks can absorb between 3.5 ml/s to 4.5 ml/s of water. If you go faster than that, you compress the puck before it's fully saturated. This can be a useful technique, for example to create a very thick espresso with a dark roast, but generally I prefer the taste of espressos that have a complete preinfusion (fully saturated puck) before rising in pressure.

The "Pressure profiled shots" on the DE1 are in fact flow profiled during preinfusion, and then switch to Pressure profiling, now that the puck is actually providing pressure. Here is our Default pressure profile, annotated to describe this:



I also use Flow profiling to make pour overs and tea, as well as Allongé espresso, where flow is more important than pressure. Otherwise, I usually use Pressure profiling.

But others are welcome to disagree, which is why Flow profiling is in the DE1 as well.
Bluecold wrote:The graphs and discussion above would lead me to conclude that if you had left the pressure at 6 bar, you would perhaps have slightly less volume, but a much more similar shot.
It's counterintuitive, but it's usually the case that a 6 bar shot will flow faster than an 11 bar shot.

-john

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Bluecold
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#6: Post by Bluecold »

decent_espresso wrote:I find flow profiling absolutely essential during preinfusion, when there is no pressure on the puck.
That makes sense, especially since required pressure for a given flow rapidly changes as the puck absorbs water. This does make a strong case for the ability to switch to a different mode during the shot.
It's counterintuitive, but it's usually the case that a 6 bar shot will flow faster than an 11 bar shot.

-john
In retrospect my comments weren't clear. I was under the assumption that the pressure was raised to 11 bar in an effort to increase the flow to the required level (ie, from the 6-8 bar shot). This wouldn't have helped, but still, if the poster had kept the pressure the same, instead of trying to recreate flow, the shots would've been much more similar.
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luca
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#7: Post by luca »

Bluecold wrote:Doesn't this effect invalidate flow profiling as a concept? If you want a given flow, but you have two pressures to reach that flow, it's impossible to reproduce a shot if you only have flow information.
No, it just means that flow profiling occurs by moving to the pressure closest to the current pressure that will achieve that flow. Like if you want to start off with 1ml/s flow, the machine ramps up the pressure slowly until it hits 8 bar or whatever produces that with your grind. Sure, 12.5 bar might also get you to 1ml/s, but the machine (and a barista actuating a paddle, for that matter) isn't going to go to 8 bar and ramp up through 9, 10, 11, 12 bar to get to 12.5 bar to get to 1ml/s. In any event, ramping up to do so would probably increase the flow rate temporarily whilst transitioning to the higher pressure, so it probably wouldn't be good flow profiling in any event.

I suppose if someone gives you some statement in the abstract like " 24 seconds into the shot, you want the flow rate to be 1ml/s", then it makes it hard for you to know what pressure that should be at. But (a) that's not really "flow profiling", (b) people don't usually try to extract at such high pressures and (c) if they did want to, then they could specify both pressure and flow.

But by "invalidate flow profiling as a concept" ... I think you really need to explain what you mean by that. What I can tell you is this - when I extract a flow profiled shot, it doesn't taste any different because of the existence of an alternate higher pressure that might also deliver the required flow rate at an arbitrary and particular point in time in the shot! Sometimes it's quite nice that coffee just decides how it will taste without consulting a shelf full of dictionaries, thesauruses and academic texts.
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decent_espresso
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#8: Post by decent_espresso »

Bluecold wrote:That makes sense, especially since required pressure for a given flow rapidly changes as the puck absorbs water. This does make a strong case for the ability to switch to a different mode during the shot.
I agree, and both the simple profile editor (picture above) and advanced editor (picture below) allow you to switch between pressure and flow profiled sections in a single espresso.

Here, for instance, is the Londinium profile, authored by Decent user Damian (and it's a very popular one) which uses pressure profiling throughout, except at the final step.



Note that you don't need to be a genius to use these abilities of the DE1. You can tap on a profile to load, it, and press the START button.


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RapidCoffee
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#9: Post by RapidCoffee »

decent_espresso wrote:I find flow profiling absolutely essential during preinfusion, when there is no pressure on the puck.

Purely pressure-based espresso machines that describe preinfusion with terms like "3 bar" are giving you some sort of flow rate, dependent on the flow constrictor, and not 3 bar on the puck. The pressure that exists during preinfusion is only that of the flow constrictor on those machines. During preinfusion, the puck is not yet providing backpressure. Only by getting your scale out can you figure out what flow rate those machines are giving you.
I made the same point in my review of the DE1, and it's important enough to bear repeating:
The initial extraction phase is (misleadingly) called preinfusion. In this phase, water flows into the puck and saturates the grinds. The dry puck offers little resistance to flow, and pressure is close to zero. As the puck saturates, the coffee grounds swell, resistance increases, pressure builds, and flow slows...

Some machines provide a "low pressure" preinfusion step (e.g., 3 bar), but this refers to pressure at the pump, not the puck. Pump pressure is only indirectly related to flow rate... During preinfusion, puck pressure is close to zero, and so it makes more sense to specify preinfusion in terms of flow rate. For example, a puck should saturate twice as fast at 8ml/s as 4ml/s.
All machines "preinfuse" to some extent, although those with larger flow rates (e.g., my rotary pump Spaziale) saturate the puck very quickly. Preinfusion flow rate makes a big difference in the extraction. As a general rule, lighter, more acidic roasts benefit from slower preinfusion, whereas darker, more traditional espresso blends work well with faster preinfusion.

FWIW, I did not appreciate these nuances until I had some time to play with the DE1.
John

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Bluecold
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#10: Post by Bluecold »

luca wrote: But by "invalidate flow profiling as a concept" ... I think you really need to explain what you mean by that. What I can tell you is this - when I extract a flow profiled shot, it doesn't taste any different because of the existence of an alternate higher pressure that might also deliver the required flow rate at an arbitrary and particular point in time in the shot! Sometimes it's quite nice that coffee just decides how it will taste without consulting a shelf full of dictionaries, thesauruses and academic texts.
Before continuing this discussion, which I think is interesting, let's try to agree on what the concept of flow profiling is.
As far as I understand, flow profiling is a way to reproduce a shot which isn't exactly the same, by prioritizing flowrate equivalence over pressure equivalence. Ie, you have shot A, and shot A is amazing. Shot B will, despite your best efforts, not be exactly the same. Shot A is defined by dose, grind, pressure profile, flowrate profile and a host of other factors. Flow profiling advocates would say that one should try to keep the flowrate profile the same to reproduce shot A as closely as possible, even if it means sacrificing pressure profile equivalence.

Can you agree on this?
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"Though I Fly Through the Valley of Death I Shall Fear No Evil For I am at 80,000 Feet and Climbing."