Accounting for Total Brew Temperature Stability

support

Jun 06, 2008

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