Gauges
When your coffee extraction begins, the coffee machines pump will push water through the grounds. The gauge will shoot up and sit briefly at around 10 bars of pressure, then it will slowly reduce back down and should settle between 8.5 - 9.5 bars of pressure.
The boiler pressure gauge on most espresso machines measures the pressure of the water tank as well as the pressure that is forced through the espresso. The pressure for brewing should be between 9 and 10 atmospheres. The espresso machine pressure has the essential role of forming the aromatic and volatile crema, and without this component, espresso would only be strong drip coffee.
