Accounting for Total Brew Temperature Stability
I am posting one more item around our recent WBC-protocol temperature stability tests of the Slayer prototype espresso machine. The graph above shows how the two different probe devices we used read and registered temperature and temperature change. The main difference between the Scace meter and the custom K probe device we put together in shop is response time. I think we may have also gotten a small advantage in terms of precision with the K as well, but no one has really sorted through the data to determine this, yet.
When K-probes respond faster than T-probes . . .
Anyway, we were surprised at how slowly our brand new Scace meter responded to changes in temperature. It took around ten seconds to register the actual water temperature coming through the system (C-A). The Scace then continued to read brew temperature for 3-4 seconds after the water flow was shut off completely. We experienced this over numerous tests, at different brew temperature settings.
On the other hand our K-probe device picked up on these deltas in temperature virtually instantaneously (B-A). It took about a second to measure the water temperature coming from the system, and as soon as the brew cycle was stopped, the K-probe readout fell instantaneously, as you would expect it to.
We picked up all the data for both measuring devices using an off-the-shelf data-logger which downloads to a Windows PC.
Dynamic Response versus Static Temperature Reading
For everyone interested in brew temperature stability, accurate and responsive measurements of water temperature coming out of a system are critical. This information needs to be both precise and dynamic.
By dynamic I mean the probe-mounted sensor must reflect virtually real time results of what temperature is doing. Otherwise a lot of poor performing machines will not be identified, and top performers in this category could be missed.
Typically T-probes respond faster than K-probes, so the probe itself is probably not the problem here. The real culprit could be the potting material and most likely the positioning of the Scace probe in the device itself (see illustration above, courtesy of Home Barista.com), even when reconfigured according to the WBC guidelines, essentially moved away from being directly under the diffusor screw (in the case of LM and other group designs with this type of diffuser block configuration).
Eric Perkunder
Posted under Equipment, Experiments & Tests, Lever Machines
Have you contacted Greg to discuss your findings? I’d be curious to hear whether he thought you got a defective unit, whether he agrees that these are design failures, or alternatively, whether the potting material was designed to reflect the temperature change of a coffee cake in the water (and thus that the slower rise to temp and slower fall perhaps illustrate the limitations of what is achieveable with water temp stability).
Thanks for your comment. First off, I am not suggesting that there is a “design failure” with the Scace. My comment is in no way meant as an indictment of anyone or any product. In fact, I love that Greg came up with an actual tool for the purpose of measuring water temp and pressure, purpose-built for our industry, especially one that looks so robust and professional. What I am saying is that I am just not convinced from my own test experience that the Scace tool responds quickly to changing temperature/water conditions–this could be because of the probe configuration, components, or material choice (as you noted around the potting compound). One thing’s for sure, there is always room for improvement–and this may be one of those opportunities for someone.
Eric
My personal opinion on this is that the valuable information is what is coming out of the machine where it hits the coffee. While I like the scace meter in the sense that it simulates coffee in the portafilter, I am not convinced that it truly does justice to some of the equipment that is now coming out into the market. For example, and please feel free to correct me…If I am testing a HX machine that begins its cycle at 212F and drops to say 205F during the brew cycle, it will register on a scace meter as a relatively quick ramp-up to 205 and hold steady, whereas a bead probe mounted in the screen or diffuser screw would register the true brewing temp of the machine instantaneously, showing the initial spike in temperature and the stability (or lack of) throughout the brew.
Also how does one consider stability and temperature between single, double and triple baskets?
Just my 2 cents
Dan
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