If the three prosumer HX machines mentioned in the how-to had different pressurestat settings and yet their temperature profiles were similar, what's the "right" setting?
For prosumer HX machines (e.g., Andreja Premium, Giotto, Bricoletta, Mia, Valentina, etc.), the pressurestat setting is a tradeoff of the desired brew temperature, steam quality, recovery time between shots, flush amount, and flush frequency. I generally set mine as low as possible (1.0 bar) but that varies from machine-to-machine. Most set their pressurestat somewhere between 0.8 and 1.2 bar (measured at the top of the cycle), and then determine the flush amount to bring the group to the target temperature. The pressurestat setting is therefore just one part of the equation. But how does this setting correlate to temperature? Recall the following table shown in the article:
- Pressure (bar) = Boiler's water temperature (Fahrenheit)
1.0 bar = 253F
1.1 bar = 255F
1.2 bar = 257F
1.3 bar = 259F
The "right" setting for a prosumer machine is thus the pressurestat setting that meets your drink preparation pace, and to some degree, your experience level. However keep in mind that commercial HX machines in general are less influenced by the flush because of their heavier groups and larger heat exchangers. Futzing with the brew temperature outside of the boiler's "comfort zone" by flushing requires more attention to timing the length of the flush and the rebound time, which compared to prosumer machines is very short (e.g., 10 seconds or less).