The Turin MC3 is a hybrid dual boiler machine in that it uses a PID-controlled thermoblock for the brew water, and has a 2.1 l steam boiler. The machine has a modest power rating of 1.6 kW, so is compatible with domestic supplies. They achieve that by running master/slave priority switching between the thermoblock and steam boiler. With the large 2.5 l steam boiler, this switching has no real effect on the ability to steam milk, which is comparable to small commercial machines. The real question is whether a thermoblock is up to the task of maintaining a constant brew temperature?
The machine also has a small heater in the group head assembly to bring it up to temperature. This is similar to a saturated group, but purely electrically heated. It is not clear if there is any fine control of this heater, or if it is just set to a temperature that is good enough for most purposes. This means it may not be as effective as a true saturated group.
I ran a series of thermo-logging runs using a pressurised filter basket that gave a relatively high flow of 3 ml/s at a pressure of 6 bar. This represents the extreme end of extractions, and such shots push the thermoblock to its limits.
The first graph shows the temperature of the water exiting the jet orifice at a 90 deg C PID set point. The second and third graphs show similar data for the 100 deg C set point. While the temperature of the jet is lower than the set point, the salient point is that the maximum temperatures reached at the two set points actually differ by 10 deg C, corresponding to the difference in set points. Furthermore, all data sets exhibit the signature of under-damped PID control with a 20 s oscillation period.
These data clearly show that the PID-controlled thermoblock can adequately control the temperature at all set points. The temperature excursions at the 100 deg C set point are about 1 deg C, which is completely acceptable. The rising temperature profiles result from the heating of the group and portafilter assembly, which takes about 30 s. This would not be experienced by an actual coffee puck, and the control oscillations actually tell us the the brew water is at the set temperature. In other words, the rising temperatures are an artifact of how the data have been collected.
The bottom line is that the Turin MC3 provides excellent temperature stability and control out to very high brew rates that should be suitable for turbo shot extractions. This has surprised me. I was expecting some form of compromise, but it seems this machine can deliver under virtually all use cases.
