I have no idea what you mean by this comment. The Aurelia is a heat exchanger. And all machines benefit from a flush.

Endo wrote:Apparently the Baristas at the WRBC were flushing it like a regular HX machine. So much for sophistication.

That's because they lose a tech point per drink if they don't do a cleaning flush on the machine, whether it's an HX or DB. Three points is often enough to move someone in or out of the finals. Check the score sheet and the recent standings.

As far as I know, the Aurelia is the only machine on the market that needs absolutely no flush either after idle or after any sort of use pattern for temperature stability.

I stand corrected: all machines except the Aurelia. Be nice to know how they accomplish that magic.

"Tech point". That's a good one. They should lose a point for flushing already stable machines.

The Aurelia sounds like an interesting machine. If they can use the steam source as the pre-heater and still control brew temp without a flush (and use fresh brew water at that?), then this sounds like the perfect solution.

RapidCoffee wrote:I stand corrected: all machines except the Aurelia. Be nice to know how they accomplish that magic.

No magic. Have the flow rate on the thermosyphon adjustable, and the group is at a fixed temperature X. Adjust the length of the heat exchanger and boiler temperature so the flow out of the HX is also at temperature X. And for the real trick, adjust the relation between the thermosyphon return and the cold water inlet so that just enough cold water flows into the group at the start of the shopt to temper the overheated HX water, also to X.

Two years ago, at the SCAA, Greg Scace was more or less trying to ambush the machine ("nobody expects the temperature inquisition") to get it to read something other than 93C. He never did.

The NS people didn't think this was a big deal, since high end machines had been tunable like this since the E61 (the "prosumer" models leave all the required jets and valves out). However, they were proud to have made an exceptionally stable model. What they did find astonishing is that the WBC wanted the machines tuned to a flat profile; since the SOP is to tune a humped one.

shadowfax wrote:I was quite impressed by the video in the Appia Tour, and that thing is not even as big (or, presumably, as stable) as the Aurelia. If you didn't see the (quite short) flush and the ~20s wait, you'd swear that was a double boiler temperature curve, yes?

The Aurelia is a different beast. Comparisons with the Appia are inappropriate. Har Har.

-Greg

RapidCoffee wrote:I stand corrected: all machines except the Aurelia. Be nice to know how they accomplish that magic.

Actually most of the machines that we tested for the WBC machine trials last year were capable of walkup shots with no flush. The flush is mandated because it's considered good practice to clean the dispersion screen off prior to brewing.

-Greg

another_jim wrote:No magic. Have the flow rate on the thermosyphon adjustable, and the group is at a fixed temperature X. Adjust the length of the heat exchanger and boiler temperature so the flow out of the HX is also at temperature X. And for the real trick, adjust the relation between the thermosyphon return and the cold water inlet so that just enough cold water flows into the group at the start of the shot to temper the overheated HX water, also to X.

The Aurelia has a very nice scheme for tuning the group temperature so that it idles at the right brew temperature. It's clever and easy for technicians to tune.

Two years ago, at the SCAA, Greg Scace was more or less trying to ambush the machine ("nobody expects the temperature inquisition") to get it to read something other than 93C. He never did.

The NS people didn't think this was a big deal, since high end machines had been tunable like this since the E61 (the "prosumer" models leave all the required jets and valves out). However, they were proud to have made an exceptionally stable model. What they did find astonishing is that the WBC wanted the machines tuned to a flat profile; since the SOP is to tune a humped one.

Actually they did think it was a big deal. They had worked quite hard on it, and were justly proud of what they did. I should clarify that WBC doesn't want flat profiles at all. They just want something repeatable under a variety of duty cycles. Currently the state of espresso machine design is archaic enuff that no machine seems capable of producing other than flat profiles if one is interested in all duty cycles. FWIW the usage in competition resembles intermittent duty, not a busy bar.

Manufacturers reps at the WBC machine trials had the liberty to set up their machine as they desired, when we did usability tests. Test baristas included James Hoffman, Heather Perry, Bronwen Serna. Coffee supplied was Heather Perry's WBC blend and some others that I can't remember. But the coffees performed best on the most reproducible machines. Coffee taste improved on machines lacking reproducibility when the initial temperature was lowered and the profile made more flat, compared to declining. I dunno whether or not this is because the blends were developed to suit the WBC conditions. We didn't explore it further.

My opinion on the matter is that coffee doesn't give a rats ass about what machine it's brewed on. The important things are that the brewing conditions need to be consistent time after time. It helps if the conditions are favorable for producing good tasting coffee. Perhaps declining temp profiles are good, but I don't know at this point because I don't have a machine that can produce them. But you've got a lot less to worry about if you've got a platform that's at all reproducible. Now you can begin to think about sourcing good coffee and doing a good job of roasting. So hx or db doesn't all that much matter if the thing can reproduce. Now if you want to get into a discussion about the ease of achieving engineering goals using... Uh, had to go bail my kid out of daycare or pay the late fee..

Oh, yeah, where was I. Right! Ease of achieving engineering goals - I think it's easier to get reproducible results, with less fiddling about and less potential for machine behavior change over the long term if the steam boiler and brew boiler are decoupled from each other - the double boiler scheme. The newest designs do a better job of managing heat loss in the brew boiler, so that the machines are truly capable of walkup shots. Smaller, more dynamic brew boilers are capable of being adjusted quickly and easily to produce specific temperatures, without affecting steam pressure, and without having to change jets. With properly designed double boiler systems temperature changes from a setpoint controller map one-to-one with temperature change at the coffee. This makes machine setup easier.

WRT engineering "elegance" - an elegant solution to me is the simple solution that satisfies the requirements. I don't really think of hx designs as elegant. Thermosyphon groups, re-entrant heat exchangers, group jets, thermosyphon flow-control valves, are all elegant (particularly the thermosyphon concept) solutions to problems that are easily avoided in the first place, just by separating steam production from hot water production.

So why did heat exchangers come about? I'd like to know more about this if anyone can point to an evolution tree. My guess is that the heat exchanger was originally developed as a method of providing fresh water to lever machine groups. This would have been a big advantage over lever machines with groups fed from a large boiler. I'm guessing that baristas and engineers learned that the relatively colder water from a small hx required less cycling among the lever groups to keep the temperature down to levels that produced good coffee taste. This would have pointed engineers toward the next logical step of developing schemes to produce these lower temperatures without the need for baristas to cycle between groups. Heat exchangers would still have been used because that is what most manufacturers were accustomed to using. Examples of other institutional inbreeding are easily found. Just look at our own auto industry, which still uses archaic pushrod-actuated V-8 engines in trucks and large cars.

It's a mistake to think that folks who designed hx machines were idiots. To my mind, there is a clear evolutionary path that makes sense enough, and given the nature of folks to adapt what they already use. We should also keep in mind that process controllers, fast electronic thermometers, etc are fairly new compared to how temperature got measured in the '50s and '60s, when these measurements were more difficult.

I cut those guys some slack, but I also think that the time has come to move on, and prolly move on beyond what is done today as well. You'd think that in these days of modern control systems that espresso machines would be highly dynamic systems whose pressure and temperature profiles were not only reproducible, but highly tuneable and adjustable with pressure and temperature profiles developed specifically for the coffee being showcased - possibly linked via network. Note that Dalla Corte is already doing some of this, with grinders and espresso machines networked together, and remote brew parameter adjustment and fault diagnosis possible over GSM phone connection.

I also think that if we are gonna have another hx vs db debate, we should get out of home machines, even though this is home barista. Home hx and db machines exemplify some of the worst engineering in the coffee business. With rare exceptions, most of our precious machines are afterthoughts cobbled together by manufacturers who can make lots more money servicing industrial need rather than the home user. Examples of such cobbling is the use of thermosyphon groups in double boiler machines. There really is no good reason for this. The thermosyphon group works properly when there is a large temperature difference between the boiler and the group. The double boiler idea is that the brew water should be very close to brewing temperature. What gives here, other than the groups look cool and they are widely available.

-Greg

Thank you Greg.
Sanity at last.

gscace wrote:Currently the state of espresso machine design is archaic enuff that no machine seems capable of producing other than flat profiles if one is interested in all duty cycles.
...
But the coffees performed best on the most reproducible machines. Coffee taste improved on machines lacking reproducibility when the initial temperature was lowered and the profile made more flat, compared to declining.
...
So hx or db doesn't all that much matter if the thing can reproduce... I think it's easier to get reproducible results, with less fiddling about and less potential for machine behavior change over the long term if the steam boiler and brew boiler are decoupled from each other - the double boiler scheme.
...
You'd think that in these days of modern control systems that espresso machines would be highly dynamic systems whose pressure and temperature profiles were not only reproducible, but highly tuneable and adjustable with pressure and temperature profiles developed specifically for the coffee being showcased - possibly linked via network.
...
Home hx and db machines exemplify some of the worst engineering in the coffee business. With rare exceptions, most of our precious machines are afterthoughts cobbled together by manufacturers who can make lots more money servicing industrial need rather than the home user. Examples of such cobbling is the use of thermosyphon groups in double boiler machines. There really is no good reason for this. The thermosyphon group works properly when there is a large temperature difference between the boiler and the group. The double boiler idea is that the brew water should be very close to brewing temperature.

Greg, thanks for a great post. You introduced several profoundly important ideas into this discussion, which I have excerpted above. Reproducible temperatures, decoupling brewing and steaming to simplify design, flat brew temperature profiles easier to achieve, all really fundamental points. Perhaps a naive response, but why have these relatively modest design goals been so difficult to achieve for a reasonably economical price point?

In some ways, your last point is most relevant here at H-B. Large multi-group machines like the Aurelia are not geared for home use. And until very recently, double boiler offerings for the home barista were limited to the Expobar Brewtus and Spaziale S1. Now Dalla Corte, Izzo, and VBM have introduced double boiler machines. But it appears as though questionable design choices may have been made in all these machines.

Are there any prosumer espresso machines (HX or DB) that, in your opinion, embody some of the better engineering in the biz? Or are home baristas doomed to enjoy the worst of all possible worlds?