Hi All,

I recently read someone say that if they adjusted the PID on their VBM Domobar Super by 2F it made a massive difference in taste. Does anyone know what difference a change of one degree F in boiler temperature makes to brew temperature (ie. the plateau on the graph)? Is this something that is going to be influenced hugely by the position of the probe and, thus, basically incomparable? I know that Ken's lovely graphs will shed a lot of light for the Cimbali group, but I'm kind of interested in the e61 type groups, which more people seem to have.

Cheers,

Luca

(EDIT: Chanced Domobar to Domobar Super - someone pointed out that the Domobar is the single boiler, whilst the Domobar Super is the HX)

gauge pressure --> boiler temp F


1.1 --> 251
1.2 --> 254
1.3 --> 256


how much the change is translated into brew temp depends upon the system.

Here is my steam chart cheat sheet


If their VBM has the group flow restrictor, it could make a noticeable difference in the flush but the heat exchanger temperature will seek equilibrium with the boiler. I have run a 0.8 boiler pressure at top of cycle before which cuts the flushing but you need a big boiler with that low setting. My VBM has a flow restrictor and the group idles at 200-201 all day at 1.15bar.

luca wrote:I recently read someone say that if they adjusted the PID on their VBM Domobar Super by 2F it made a massive difference in taste. Does anyone know what difference a change of one degree F in boiler temperature makes to brew temperature (ie. the plateau on the graph)? Is this something that is going to be influenced hugely by the position of the probe and, thus, basically incomparable?

Barry and Dave, I think you missed that this is a (hypothetical) PID temperature controlled boiler, not a pressure controlled system.

Luca, I have no idea. Changing the temperature gradient by two degrees F would seem to be a small change. I wonder if there may be a point in the steam boiler temperature that may have a drastic influence on the E61 thermosyphon behavior that may result in large brew temperature changes?

Luca -

I recently read someone say that if they adjusted the PID on their VBM Domobar Super by 2F it made a massive difference in taste.

Working backwards from the 2.0 degree change in boiler temperature, this results in a pressure change of ABOUT 0.05 bar. That pressure change results in a grouphead temperature change of ABOUT a little over 1.0 degree in the Quickmilll machines. I suspect that the same would hold true for Vibiemme but . . . ya never can tell.



It is possible to set a PID (and likewise, a pstat) on many of the machines discussed here such that one could simply walk up to the machine and pull a shot. Machine recovery would suffer as would steaming.

Later on today or tomorrow, I may try that just to see what difference it makes in thermofilter results. But, I would foresee about a 1.0 degree change in average brew temperature and this all gets back to the sensitivity of one's taste AND the sensitivity of the particular coffee.

luca wrote:I recently read someone say that if they adjusted the PID on their VBM Domobar Super by 2F it made a massive difference in taste.

Please don't exaggerate. The OP said the 2F change removed a defect. No mention at all about massive, Mate!

As Ken Fox has so ably shown, it's about a 2 : 1 ratio for boiler to brew temp adjustment.

luca wrote:Is this something that is going to be influenced hugely by the position of the probe and, thus, basically incomparable?

Assuming the probe in question is the boiler probe, regardless of the position, a 2F change in boiler temperature is the same. The likelihood that a 2F boiler delta produces the identical brew delta on another machine is probably unlikely.

luca wrote: Is this something that is going to be influenced hugely by the position of the probe and, thus, basically incomparable?

I believe that the position of the probe can have profound effects on the machine's behavior. What kind of reading the probe is getting depends on its placement in relation to things like the incoming water supply currents and the proximity to the heat element.

When I was considering some modifications to my previous machine, I exchanged a couple of brief emails with Sean Lennon for advice. He pretty much confirmed my above statement with his experiences. He further went on to state that when PID'ing a few Brewtus machines, they all demonstrated different characteristics in temp stability - some benefited from insulated boilers, while for others, the insulation had a negative impact. As you know, these are all similar DB machines. I would imagine that the variances with an HX would have the potential to be more profound.


Matt

Matthew Brinski wrote:I believe that the position of the probe can have profound effects on the machine's behavior. What kind of reading the probe is getting depends on its placement in relation to things like the incoming water supply currents and the proximity to the heat element.

No one would doubt this.

The topic is how changing HX boiler temp affects the brew temp. Brewtus is not an HX. Amica and Alexia are not HX. Incoming water has minimal effect as the water is injected into the HX and is completely isolated from the boiler probe.

Regardless of where an HX boiler probe is located, changing the set point will change the brew temp once the machine has restablizied, assuming the barista does not change the build process.