Each blend of coffee is the result of the selection of coffee varieties and processing techniques: nevertheless, even if the best raw materials have been chosen and the techniques used are the most sophisticated, for a perfect extraction of the coffee in the cup is important that the machine and the grinder are properly adjusted, and that the bartender uses them correctly.
The pressure due to enhance the creaminess and correct extraction, together with the water temperature. On average we use a coffee pressure of 9 atmospheres that can vary according to the tastes that you want to enhance from the same mixture, such as the degree of acidity, bitterness, sweetness. With a calibration that is too low the coffee would be under-extracted, on the contrary with a higher pressure the same would be over-extracted.
The correct operating parameters of the espresso machine, although varying according to the make and model of the machine used, can be summarized as follows:
Boiler pressure: 0.95 bar ± 0.05
Pump pressure: 9 Bar ± 0.5
Temperature: 90 ° C ± 2
Extraction time: 25 sec ± 2
Dose grams: 7 g
Volume in cup: 25 ml ± 2 (in 25 sec.)
Cream height: 2-3 mm
Pressure of the pump: the pressure gauge lever, during coffee extraction, must be in the green zone, between 8 and 10 bar (correct pressure 9 bar). As the pump pressure increases, delivery speed increases, and time of coffee extraction.
Boiler pressure: it can vary between 0.9 and 1.1 bar; between 0.9 and 1.0 for machines that use relatively few coffees during use, between 1.0 and 1.1 in the case of machines that work a lot (more than 50 coffee / hour) and use boiler water for cappuccinos and tea. The boiler pressure is directly proportional to the temperature reached.