Temperature surfing an HX espresso machine?

#1: Post by **EricL** » February 17th, 2009, 5:20 pm

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.

#2: Post by HB » February 17th, 2009, 6:26 pm

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.

February 17th, 2009, 10:47 pm

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.

#4: Post by **Ozark_61** » February 18th, 2009, 12:45 am

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.

February 18th, 2009, 12:45 pm

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.

February 18th, 2009, 7:42 pm

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.

December 5th, 2009, 12:30 am

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

#8: Post by **RapidCoffee** » December 5th, 2009, 8:46 pm

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.

#9: Post by HB » December 5th, 2009, 9:23 pm

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!

December 5th, 2009, 9:24 pm

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