We were very fortunate enough to have 3 very investigative professional baristas to visit us last Saturday.
Not only they brought beans but also a scace 2 for us to see how Bosco Spring Level pressure and temperature works.
Within the short afternoon we concluded the following:
We did two rounds of routine to have more data to reduce one offs.
Each measurement were measured as if we were making espresso/ milk base drinks
A Espresso making: with 30 sec between shots
B Milk base drink: 45-55 sec in between
A & B pressure unchanged
Both case starts off low at 5psi at preinfusion stage
Ramps up to 95psi 6.55 Bar only ! at highest pressure +/- 13 sec on releasing +/-10sec
Drops dramatically to almost 0 at 30sec
Pressure does not change from steaming or pulling shots on other group as all independent.
A & B didn’t seems to affect much this time
If machine is left on standby, first shot temp is roughly 83c highest at 5s (from the moment you pull the lever) then drop 3c through out.
On same routine, 3rd shot highest reach 91c
Only at 5th shot it reaches 93.2, drops 3c again during shot
Then temperature of water at
this stage seems to reach a fairly constant point and drops consistently a 3c lower from 93.2c during extraction.
At first we couldn’t figure out why lever machine taste so nice with such low pressure, but thinking carefully we believe the long contact time of hot water to coffee helped. The whole process is about 35sec.
Moreover, after preinfusion on releasing the lever, pressure rise is very instant, then drops smoothly. That means the the nicest part of the grind is extracted with highest pressure and temperature. As extraction continues, the fall in temperature and pressure extract less of the unwanted taste from grind. So making a ‘fine tuned’ espresso.
All was very revealing to understand how machine actually behaves.
Now we really wish we have stable temp machine that doesn’t need so many warm up shots and with a 9 bar pressure side by side to understand properly! Best if one can change actual
brew pressure to double check what constitute the whole brewing and affect the taste in the cup to complete an investigation!!