LaSpaziale S1 Vivaldi II
LaSpaziale S1 Vivaldi II Temperature Tests
The PDF attachment below shows the results of VII temperature measurements performed five consecutive times at each programmable temperature: 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, and 97°C. The initial set of measurements were taken using the default offset of -1°C as tested and set by the Chris Coffee techs prior to shipment. In order to see the actual difference the offset makes, I repeated all measurement at offsets 0°C and at -2°C. (See Note below.)
The results showed that the water temperature over all readings averaged +1°C high with my default offset of -1°C. As expected the water temperature readings with an offset of 0°C measured 2°C higher than the programmed temperature and the temperature readings with an offset of -2°C were almost spot on with the programmed water temperature. From this data one would think I should change my offset to -2°C. However, there is one key aspect of my test methodology that does not mirror real world use. I did not remove the portafilter between tests which would have simulated additional cool down of the PF and group while coffee was being loaded. Below is Chris Nachtrieb's explanation of how his techs test and adjust the offset before each VII is shipped:
We test each machine and set the offset accordingly. Some machines 0°C offset, some -2°C, some -1°C. We use the Scace device and a digital Fluke.
Here is how we perform the test to calibrate.
The 30 seconds represents the time it take someone to grind and tamp coffee before putting the portafilter back into the group. We repeat it three or four times before making any adjustments.
After reading Chris' description of testing, I set my VII back to the -1°C offset at 95°C. I reran the tests the same as I had previously except that I removed the PF between shots just as Chris described above. This time my readings ranged from 94.9°C to 95.6°C for an average of 95.3°C. Given that in real use adding the coffee and tamping with a stainless steel tamper will remove a little more heat than just letting the PF sit out of the group for 40 seconds, I think the -1°C "factory set" offset is exactly right for my machine. My recommendation is for VII owners to leave the offset as it is and just use the standard water temperature adjustments to optimize their coffee extraction to personal taste preference. However, if you wish to adjust the offset, here are the instructions.
Note: Offsets are programmable in 1°C increments from 0°C to -8°C. This seems backwards since one would think that there would be a temperature drop between the boiler and the group head thus requiring a positive offset to make the water temperature at the group equal the water temperature in the boiler. According to Chris Coffee, the theory is that the VII software programmer already has hard coded in an offset that is too high. Therefore the new programmable negative offset provides a way to counter that.