Getting accurate shot temperature displays on PIDed double boilers without a thermometer - Page 2

#11: Post by **ailevin** » October 27th, 2018, 7:24 pm

I haven't done the experiment with my DB Vetrano, but with my HX Vetrano the GH would idle 3-4 degrees F hotter with the bottomless portafilter. Apparently the ability of the regular portafilter to act as a radiator into the room was more significant than adding thermal mass to the GH. I will be interested to see if your results change at all.

Thanks for doing the experiments and posting the method.

Alan

October 27th, 2018, 9:37 pm

ailevin wrote:I haven't done the experiment with my DB Vetrano, but with my HX Vetrano the GH would idle 3-4 degrees F hotter with the bottomless portafilter.

I just tried it; there was a 1C drop in the group (the flash boil point moved up to 101C). Maybe with the smaller difference between boiler and group temperatures in a DB than an HX, there is a smaller effect on adding more heats sinking.

#13: Post by **maki** » October 28th, 2018, 3:08 am

i am interested in that video, preferably for some points to make it easier to differentiate say 98C from 100 or 102C?

#14: Post by **ShelbiRyan** » October 28th, 2018, 11:29 am

Great information, I have a Profitec Pro 700 which I'm sure many know, had issues with offsets when changing from C to F. I'm curious to see how this method will line up to my current offsets. I too would also be interested in a video as a reference point.

October 28th, 2018, 7:07 pm

maki wrote:i am interested in that video, preferably for some points to make it easier to differentiate say 98C from 100 or 102C?

I've added a video to the first post

October 28th, 2018, 8:36 pm

It looks to me that they all reach the point of steaming, bubbling, and boiling, with the only significant difference being the time it takes, and the hotter you get the more aggressive it is.

It is interesting too that they all coalesce to a single stream. My E61 never does that with a Lelit or IMS screen. It looks like the bubbles are causing the coalescence.

October 28th, 2018, 9:10 pm

When you watch water coming to a boil in a pot, you'll see it start to steam and bubble starting about 95C, and getting more energetic as it gets hotter. At 100C, the entire body of water boils. It's the difference between "simmering" and a "rolling boil".

Also, the brew boiler is well over the boiling point, at panel temperature + offset. This means that the stream will heat the group and come to a rolling boiler eventually. You are looking for an almost immediate boil (there will always be some water in the group bell below boiling). The video shows this quite clearly, at 99 it comes to a boil at around 6 seconds; at 100, its almost immediate.

#18: Post by **RyanJE** » October 28th, 2018, 9:57 pm

I played around with this in past so it's interesting to see from someone else's point of view. The one thing I always wondered (maybe specific to e61s) was about flow rate. Wouldn't the offset need to be higher when the flow is slowed down to normal brew rates? I think since the water moves faster from boiler to group with no restriction it loses less heat than it would with coffee...

I also observed on a Quickmill Alexia with Eric's e61 thermo that flow rate significantly influenced actual brew temps. Slower flows were much cooler as heat was lost... when Scace tested the offset would be reliable every time since the flow rate on a Scace never changed from shot start to finish...

Because of all of this, I actually thought it was odd to have a machine like Vesuvius where one would profile pressure and flow because there's an inadvertent temp profile as well. And now Bianca too it would appear.

I sense this is a non issue in actively heated groups?

October 28th, 2018, 10:40 pm

The goal of the calibration is to set the panel temperature to the group temperature, which is also the initial shot temperature. Your post raises two issues. The first is whether this is appropriate, the second is how flow rate affects the measurement process.

If you want to explore the temperature dynamics of the shot, you need a Scace thermofilter, Schomer PF, or something equivalent. The shot may have a rising, flat or falling profile. But these dynmaics have no bearing on the offset, since it is a constant. For the offset, you have to pick one temperature. I'm convinced the only possibility that is easy to standardize is the initial shot temperature, which is roughly the same as the group's idling temperature.

The flash boiling method is meant to set the offset so the panel displays this idling group temperature. The second issue is when the water debit is high, and the group is light, the water will not have time to equalize temperature with the group, so the flash boil will occur when the group is cooler than 100C. Since most DBs have heavy groups and reasonable water debits, I'm hoping this won't happen.

October 29th, 2018, 12:27 pm

That all makes sense. What I was thinking was, what happens to the temperature of the water once it leaves the boiler comparing flow resistance and no flow resistance? With a packed coffee puck, lets just say it takes about 8 seconds for boiler temp water to get from the boiler to the exit of the group. AND, there is a lot less of it moving due to the OPV / Bypass, etc. Along the way its arguably losing heat in a SBDU e61 since there's tubing inside the unit and a typically cooler group (may not be the same issue on an HX with an overheated group). With no puck a higher volume of boiler temp water rushes from boiler to group in basically 1-3 seconds. Wouldn't that not lose as much heat along the way?... Would that affect a true offset?

My only hang up with the Scace is that I dont think it simulates dynamics of a real shot since its flow rate is pretty linear vs a shot that dramatically increases in flow during the shot. That may not be the same issue when testing using flow profiling machines.