My short list for upgrade is down to 3, (come on April 15, get here already) but have a question about temperature surfing with the VBM Domobar Super.

I've read the various threads on temperature surfing, but I'm not sure what is different about the Domobar Super. Let's say it's adjusted for a stable 200 degF like in the review, and I'm pulling a shot with Vivace Dolce with a recommended temp of 203.5. Can I do a flush and recover, and start the shot at 199 on the EricS group thermometer?

I know it is all about the taste, and in the end on any coffee it's experimentation to fine tune, just curious if there are limitations placed on the brew temperature by the thermosyphon restrictor.

Thanks.

You can manipulate the brew temperature outside of most prosumer/semi-commercial HX espresso machine's "comfort zone" a couple degrees up or down, but it's difficult to go outside of that range (say 198 to 202F) without changing the pressurestat setting. For example, if your target brew temperature is 204F and the pressurestat setting is too low, lengthening the recovery time after the flush or shortening the flush itself will distort the brew temperature profile.

In other words, to produce a reasonably flat brew profile, the group must be within reasonable range of the brew temperature. Trying to "trick" the group into producing radically lower or higher brew temperatures doesn't work well for most prosumer/semi-commercial HX espresso machines and fails miserably if it has a flush-agnostic commercial group like the La Cimbali Junior.

Thanks, that makes perfect sense. It's seems like a balanced system that's always trying to maintain equilibrium. I imagine different techniques help you explore the upper or lower end of the comfort zone, flush & recover may be better for the lower end, flush & go or blind flush may be better for the upper end?
All I can say is the wait for the new machine is killing me.

Dan is right on. You're also on the right track with EricS' thermocouple adapter (absolutely necessary accessory!).

Just to add - if you want to have a cool shot, then you need to overflush (compared to your normal shot), and then wait the right amount of time to have a constant brew temp (longer than your normal shot - if you want a flat profile). If you want a hotter shot, then you underflush and have a shorter recovery time. You might want to use a stopwatch in the beginning to get a better idea of how to manipulate the variables. After a while, you'll get a better feel for how to pull a 201' vs. 205' shot.

Different set-ups will tend to favour a particular sweet spot. My Elektra runs at 1.05 bar at the top of cycle. That tunes it into the 199-201 range depending on the flush. I can get lower and higher by varying the flush and recovery time but at that setting, it wants to run around 200. Right now I am working a coffee that takes a higher temp, 202. So I have to flush 3 seconds and wait 10 seconds before I pull my shot to get 202. If I had the boiler at 1.2 bar, a 3 second flush and 10 second wait would get me another flash boil. You just have to play with you system and learn how it responds. Eric's adapter will help you.

This is where experience comes into play. There is no magic bullet, you just have to pay attention to what you are doing and see how the coffee tastes. Then adjust accordingly. After a few months you wont need the adapter any more because you know how your machine will respond. This is where a double boiler shines. You just set the temperature you want and go, which is handy but you pay a premium for that. I can reliably get half degree or less target temperatures on my HX machine on the fly. No need to make a PID change, wait 15 then try again, just adjust the flush a little and pull another shot.

Once I upgrade I'll have to see about getting my hands on a scace thermofilter. It would be informative to run a series simulated shots to show thermal performance over time. I'd love to see for instance if you do a flush & recover to various temps (down to 180, 185, 190, etc.) do the recovery curves line up, and test limits or what you do around the sweet spot, and where the linearity of the temperature curve starts to break down. Sounds like a good experiment for a rainy afternoon. I've already seen where someone has charted the steady state grouphead temp's for a VBM at different pressure stat settings.

A quick way to judge visually & it works on my Bezz
Lock in an empty group handle
Turn on machine to flush
View the water cascade and when it runs like an ideal coffee pour turn off
It will be spot on temperature
Then load tamp & proceed with your coffee extraction as normal

KK

Koffee Kosmo wrote:A quick way to judge visually & it works on my Bezz
Lock in an empty group handle
Turn on machine to flush
View the water cascade and when it runs like an ideal coffee pour turn off
It will be spot on temperature
Then load tamp & proceed with your coffee extraction as normal

Espresso flow rate is about 1ml/sec for singles, 2ml/sec for doubles. The unimpeded flow rate is many times this (7-8ml/sec on my machine). Espresso pours as crema, and looks nothing like water at any flow rate on any machine that I've ever used. The comment about temperature is even harder to justify.

No disrespect intended, but I don't see how this can possibly be correct.

I assume Paul refers to how the water calms down during the flush. This transition is especially easy to see on "Dragon" espresso machines like the Olympia Maximatic, Elektra A3/Semiautomatica, and I presume the Bezzera. From Olympia Maximatic - Second Look:


Hint: Don't watch the video, LISTEN to the video!

The questions was

Temperature surfing an HX espresso machine?

The method I use and posted is more to do with how to consistently judge a cooling flush that has a visual sign

I suggest you try the method & report back on your observations

KK

Strangely I find the same type of audio cues in steaming milk. Milk will talk to you and tell you when it is done steaming by sound more than it will by a thermometer.

-C

HB wrote:I assume Paul refers to how the water calms down during the flush.

That was my understanding as well.

Koffee Kosmo wrote:View the water cascade and when it runs like an ideal coffee pour turn off
It will be spot on temperature

Apologies if I've misinterpreted your post. I'm assuming "coffee pour" refers to an espresso pour. If so - no, the end of the water dance does not look the slightest bit like an espresso pour to me. And the temperature comment sounds like a flush & go recommendation, which is not optimal for all machines.

No problem RC
I do understand and agree on what you are saying in that it may not be optimal for all machines
Many other factors also come into play over and above the machine design

But its a good way to learn about cooling flushes and the method has a repeatability factor
I have also observed that in summer a cooling flush runs longer in time than in winter

It may just be that it works on my machine
KK

Koffee Kosmo wrote:It may just be that it works on my machine

No doubt. I expounded on this point here and excerpt it below:

HB wrote:Having written a number of reviews, I've come to recognize differing degrees of how heat exchanger-centric a particular espresso machine is. My shorthand for these distinctions are:

• Dragon - key characteristics are lots of flash boiling, fast recovery, nearly zero thermal memory, and slowly rising brew temperature profile. Simply stated, after the cooling flush, the heat exchanger output is the brew temperature. Examples include the Elektra Semiautomatica, Gaggia Achille, and the Olympia Maximatic.
• Mixer - key characteristics are modest flush, medium to slow recovery, considerable thermal memory, and initial rising then falling brew profile. Unlike the Dragon, the Mixer's brew temperature isn't determined solely by the output of the heat exchanger. Other factors, such as cool water mixing via an heat exchanger injector, backflow from a thermosyphon, and the attenuating effect of a heavy grouphead temper the final brew temperature. Examples include HX E61 espresso machines like the Vibiemme Domobar Super and Quickmill Vetrano.
• Agnostic - key characteristics are small, fixed volume flush or none at all, and long thermal memory. Careful tuning of a Mixer with tweaks in the design can produce an espresso machine that is heat exchanger in name only. Examples include the Cimbali Junior and Nuova Simonelli Aurelia.

As the last entry suggests, these categories are not immutable. With minor modifications or boiler pressure adjustments coupled with barista techniques, an espresso machine that naturally fits in one category can morph into one of the other categories (e.g, Ian's HX Heaven or 1½ Boiler).

I need to integrate these points into the HX Love article.

Back to your comment, Jim will be posting a review of the Bezzera BZ07. He reports that it's a "Dragon" type HX that responds well to the flush-n-go technique you describe. Some HX espresso machines (e.g., Quickmill Anita/Vetrano) fare much better with the flush/rebound technique described in HX Love; others are somewhere in between (e.g., Vibiemme Domobar Super).