@Pizzaman383 yes, exactly.

For some reason I was thinking (hoping) that it was actually measured as the flow was coming out of the portafilter.
You know and it just clicked of what led Rao to put the filter above the puck.

@luca, first I must apologize because I am on my phone so my responses are all around discombobulated.
I was asking flow/pressure for the DE, yes it does matter. And unfortunately this is the main reason why most technology and code is trash. I am truly sorry for that. Because the feed back is coming from the response that the thing did what it was supposed to and not on how it affected the system. And why it make sense to have an ET and BT probe. Hence why in this system flow and pressure are tied. Limited, or rather, acted against by the resistance either by the puck or the portafilter holes. So the total puck environment is not acted on equally (unless you put an equal resistance above And below the puck). Flow will determine how much pressure needed to achieve a rate. Pressure will result in a rate and alter temp inevitably simply because the puck is at a lower temp than the water.

I wouldn't worry about a pressure stat boiler you already have a more advanced machine because it creates a more precise measurement going into the system aka portafilter. The machine you'd be copying is like $100 machine you get from big box stores.

You can write out an experiment, it doesn't have to be lavish. TDS and % yield would be nice of course but I'll go out on a limb and trust your palate if you say one profile has more "x" than another.

Me, I'm just a mad scientist that majored in speculation

pizzaman383 wrote:It is easier to add heat to the group more quickly than it is to let it cool down so it might be worth trying rising temperature profiles.

Yep, will do, per my earlier post:

luca wrote:I think the next logical bite is probably looking at what we can do in changing the temp the other way. It looks like we've established that there is a limit to how much temp the system can lose across the shot (at least with the current firmware). What about how much temp the system can gain? So the next step is for me to set stage 1 to 80 C (the minimum) and the remaining relevant stages to 98C (I think that you can actually choose 99C if you want) and see what we get!

Hopefully I can do that graph tonight, then taste some shots this weekend, then have my refractometer back for next weekend.

Well according to the article by Dr Fekete, she and Craig found that 90C->95C had some pretty significant increases in aftertaste and balance compared with most of the other shots ... well, maybe 0.25 on what looks like it was probably a SCA/Q-ish scale (Craig is not just a Q grader but also a Q instructor), and up maybe 0.5% in extraction compared with the flat 95C shot. In their article, they preferred 90C->95C.

Anyway, I'd prefer to just do it, rather than speculate, since it's easy enough. I guess that, logically, it looks like 8C is the biggest drop I can get, so I should probably try flat 90C, flat 94C, flat 98C, 90C->98C, 98C->90C or some combination thereof moving the 94C midpoint to something that makes sense for whatever coffee I'm trying. There are also endless permutations of the flow profile that could impact this, so rather than getting lost on them, I'm just going to arbitrarily pick something, tell y'all what I do and we can take it from there. For example, it occurred to me I could fillet the preinfusion into two, only feed in half of the PI water at 98C, request the rest of the PI water at 80C and see what happens.

Crunchybean, I'm still not entirely sure that I get what you're saying in terms of the interaction between flow and temperature. If you're saying that high temp reduces flow rate, as Craig and Dr Fekete observed, therefore there is some dependency between the two, that's a fair enough observation, but my understanding is that the machine will counteract this by pushing at a higher pressure to get the same volume through. We can never decouple this interaction, but by using a flow profile for a segment, at least we can keep the volume of water delivered at a given temp pretty constant. But all of that's probably pretty moot the way I've set up these temp profiles, since they're just sloping and the segments beyond the initial high temp one are all set to the same temp. So I don't think we need to worry too much about it for the moment.

OK, so I did a bit more groundwork to investigate what we can do.

First question: The max temp drop above was more or less 98C -> 90C or about 8C. Maybe that shot was a little short; let's give ourselves a margin of error and say it's 9C. But the max temp drop is limited by (1) the minimum 80C temp set, which influences the group catridge heater as well as the water temp and (2) how much heat the system can actually lose; its insulation. So we speculated that the max temperature gain that is possible might be able to exceed the max temperature loss. That's all background. Is it true? Answer: Yes:




We can go from 80C to 91C, for a temp gain of about 11C. This was over a 50g shot.

Next question: Having established that we can add more temp than we can drop, is creating mirror image temp profiles as simple as setting the starting temp of the increasing temp profile to the end temp of the decreasing temp profile and vice-versa for the ending temp? Answer: Yes:




In the above example, I cut the shot ramping up at about 43g and, consequently, it didn't ramp up quite high enough to more or less reach the starting temp of the shot ramping down. Had I not preempted it and let it run for about 50g, I think we would have gotten a slightly more satisfying graph.

For completeness, I should point out that I dialled in the sacrificial coffee for this exercise to produce pressure profiles that look like what I like on the blooming espresso profile using my grinder, so, in that sense, the conditions are realistic:



Aside: The second pressure peak is what I use as my secondary reference point when dialling in (the primary reference point being what's in the cup, of course). The slope of the pressure dropoff from that peak seems to be a characteristic of the grinder/burrs (well, assuming that there hasn't been some sort of barista error in pulling the shot).

Bonus round: Having this pressure profile programmed, I wondered what would happen if I simply deleted the "bloom"/soak phase (ie. after preinfusion when the pump isn't running). The answer is that the pressure jumped up a lot, dropped off quickly, and a large part of the shot volume was pulled at a very low pressure (and looked terrible). Dosing 4g less wasn't enough to lower the pressure peak significantly, nor was grinding a whole number coarser on my EK ... on my particular dial (sigh ... can someone please make a 360 degree EK dial that becomes the new standard, so that we can talk in objective, consistent, translateable numbers?) and neither remedied the marked transition between a very high pressure phase and a very low pressure phase. I think Rao has said that the bloom allows the use of a finer grind setting and this exercise certainly showed that. So I don't think that this particular profile is going to be a productive thing to investigate. Anyway, here's an ugly graph for you of these ugly shots. Parental guidance recommended:




I feel all of that gets enough background out of the way that I can now make some shots, taste them and report back. We've also established that for these sorts of temp profiles, we only need two temp segments, so later on I can probably program a pressure profile that's more generic, like a standard e61 profile or something, with an overlaid temp profile. That way, we can sort of take more oddball temp/pressure profile out of the equation. Actually, if I can do that easily, I might do that before tasting anything and use it for the shots that I taste.

... and after all of this, I'm seriously considering referring to the machine as the temp-a-sketch ...

@Jim, presumably it is for the same reason we do not cannonball into a jacuzzi. If I were to guess, it would be mainly based on the limitations on how quickly we can heat up water and its synergistic effect when it comes into contact with coffee molecules. If I were to be scientific about it, I would say that as the water come into contact with the grounds it is seeping into the cellular structure and pores creating highways and also eroding/dissolving some of the broken down cell walls. Gaining access to the globlets of oils within the pores and fissures. CO2 and other gases trapped in the cell structure also help push out the sweet nectar of the gods, the gases are adjitated by the heat and release throughout the extraction and gain more energy (internal pressure) with a temp increase. Possibly because of the temp gradient there are more pathways of uneven resistances and/or causes the built in gases to be released more gradually. And so as the gases are released they carry with them more flavors/ oil globlets from the pores through the paths of least resistance. By this explaination it would make sense to me if more could extracted by increasing the pressure and temperature gradually.

@luca, all hail the sacrificial coffee!

crunchybean wrote:@luca, all hail the sacrificial coffee!

LOL.

Actually, this particular sacrificial coffee made me quite sad. It was some Burundi green that I was kindly donated to use as fodder to dial in my roaster. I got some surprisingly good results out of it, save that it has this amazingly intense earthy/potato aroma; I've had the extraction fan running for a while. I feel really terrible for the producers. I mean, who wouldn't love coffee producers in Burundi being paid a quality premium? I googled a bit on it and it looks like this might be caused by a beetle that not only causes this defect, but also lowers yield. Well the good news is that this is something that has had money tipped into it (some by ACE, which runs COE, I think) and I read somewhere or other that it looked like there might be some sort of pyrethrum type insecticide that might fix the problem, and is apparently able to be derived from some plant that they can grow, so it seems like it could be a pretty environmentally friendly solution and hopefully a cheap one. So I'm hoping that I see this green on the market in a year or two, sans potato ... and that the producers adopt a beetle flipped on its back as a logo.

Now there's a digression.

I'm paraphrasing a bit from the DE forum, but back in March, there was a firmware update that would "turn on group heater for low flow". It was for flow priority only though and for flows less than 0.5 ml/s.
For those very slow flows, it proved to be great as the 0.5ml/s trickle would not be enough to keep the heat in the group. If a shot would take 60s to complete the temperature would drop from the requested temp. There just isn't enough water to maintain the heat and the group constantly wants to cool.
The firmware was to be updated (I don't think it has yet, maybe I missed it) so that it triggers for all low flows (when pressure profiling too), and up the threshold to 1 ml/s.
So, from this information, we know that it's possible to heat the group independently from the water temp, though that feature is not yet exposed.
Luca, I think this is important to keep in mind in case your flows are below 0.5 ml/s with flow priority. If you're using pressure or above 1 ml/s it's probably a mute point.