A 3-way solenoid valve relieves the portafilter of pressure and moisture after the extraction. This produces a dry puck which can easily be removed afterwards. It also means that you don’t have to wait for the pressure to equalise, so that you can make back-to-back coffees.
With a pre-infusion function you get a low pressure of water before it ramps up to around 9 bar of pressure. This gently expands the grinds to get a smooth extraction and to help prevent channeling in the cake.
With a double boiler or heat exchanger system, you can brew and steam milk at the same time. This has an advantage over single boiler machines where you have to wait between brewing and steaming for the temperature to adjust.
These buttons can be programmed for different types of coffee such as an espresso, doppio or ristretto. This means once you have mastered a particular style of coffee, you can get it the same every time.
The time taken to pull an espresso shot is one of four key elements, and should be around 19-22 seconds. Once you have the grind, dose and tamp correct, you can use the shot clock to time the pull perfectly.