Temperature Stability . . . . from a Heat Exchanger - Page 3

Need help with equipment usage or want to share your latest discovery?
User avatar
Supporter ❤

#21: Post by cafeIKE »

Ken Fox wrote:If anyone else out there has a PID'd HEX machine, it sure would be nice to see this duplicated on another type of machine.
Just so you know your effort is appreciated, your post was a major influence on my decision to PID an HX when I decided to change from the Solis SL-90. I'd modded the SL-90 to get very good temperature repeatability, so did not want to go backwards. The SL-90 made great espresso for many years, but I got tired of serving whipper foam on cappas. And the e61 screams espresso to the guests :lol:

After months of compiling stats on machines I decided on the Vibiemme Domobar Super.
The PID project went very well and I insulated the boiler as well at the same time.

My goal was to be able to walk up to the machine whenever I felt like a shot and pull as good or better than the SL-90 without the temp surf delay and minimal flushing.

I've always been curious about the correlation between taste, brew temperature profile and how dosing affects them. I made up a Schomer style basket with a bead probe set in the center with the bead midway between the top and bottom of the puck.

The graph shows real shots pulled over 3 days from the same batch of coffee. The leading edge of the curves show the changes in the brew temp profile with changes in the dose and grind. Note this is the internal coffee puck temperature.

The interesting part of the graph is the flat area. Temperatures are well controlled within about 3 degrees. These shots are pulled with no flushing whatsoever and at completely random intervals from about 7 to 45 minutes. The PID is set to 232.5. The group inlet temperature hovers around 210F, rising from 209 to 211 over the course of two hours. The machine is on a timer and starts from cold at about 55F and warms for an hour before any shots are pulled.

Thanks for all your good work.

User avatar
Team HB

#22: Post by luca »

All of these posts are very interesting, but how does the espresso actually taste?
LMWDP #034 | 2011: Q Exam, WBrC #3, Aus Cup Tasting #1 | Insta: @lucacoffeenotes

User avatar

#23: Post by danblev »

Thanks Ken,
This is a great article.

It is hard to ignore that the shots temperature are all much flatter after the 15 seconds mark. Seeing this I have a (not surprising) thought that the temperature is dependent on the flow rate much more than other parameters. So here are some points that it looks like are still not controlled.
-The flow rate isn't controlled during flushing -> thus it cools the HX to an unknown temperature.
-The time from the end of flushing to start of brew is not controlled -> enables the HX to heat back to an unknown temperature.
-The packed coffee is not controlled, although it looks like Ken is a master in his ability to control the repeatability of building the puck, it doesn't adhere to most of the semi-professional readers of HB.

My thoughts about this are:
a.To take a blind basket and make a small hole in it to slow down the cool flush; thus have some control over it and have more of what is on the right side of the graphs.
b.Compare results of PID HX to listening to when the HX has cooled to your preferred temp.


User avatar
Supporter ❤

#24: Post by cafeIKE »

luca wrote:All of these posts are very interesting, but how does the espresso actually taste?
Taste? We don't need no stinking taste!
We've got numberz!!! :P

So far, since I got the Vibiemme, I've pulled two G-Shots in about 8 months. Lest you think that number low, I've been drinking espresso for more than 4 decades and the average is about 1 per decade pulled in shops.

Compared to the best baristas, I'd rate the average about an 8.5.
Compared to the ROTM 'barista', about 9.99.

Dinner party guests have made comments like:
  • - This is the best latte I've ever had
    - I've never had an espresso before that wasn't bitter
    - Wow, I don't need any sugar in this
    - Wow, the crema is like honey
Drop by and judge for yourself. :wink: