HOW IT WORKS

The principle of operation of an espresso machine is the same for all, regardless of the model. A boiler, usually equipped with a heating element, is used to produce hot water, which is then pressurized with the aid of a pump and forced through the coffee grounds.

TEMPERATURE 198°F + PRESSURE 9 BAR = GOOD EXTRACTION OF THE AROMAS AND FLAVORS SO THE AIM IS ALWAYS TO MAINTAIN A TEMPERATURE OF 198°F (SEE here)

It is, technically speaking, easy to maintain stable pressure. But temperature is another matter. It is tricky enough to keep the temperature stable during the time it takes to pull one shot of coffee, let alone when you are pulling several shots in succession. Any variations in temperature then cause inconsistency in the taste of the coffee.

HIGH PRESSURE = A QUALITY SHOT?

Some espresso machine manufacturers offer pressures of up to 18 bar, suggesting this improves the quality of the extraction. The optimum pressure for espresso is 8 to 10 bar; if it is > 10 bar, there is a risk of overextraction of the grounds, yielding a bitter coffee. Professional machines are set to 9 bar by installers, and serious domestic machines come with a built-in pressure limiter in case the pump has a tendency to become overzealous. So don’t let yourself be impressed by high numbers!

BUT WHAT IS PRESSURE?

Pressure is a force that acts on a surface. Its unit of measurement is the bar, with 1 bar equal to the pressure exerted by a mass of 1 kg on an area of 1 cm². We find examples of different pressure levels in daily life: atmospheric pressure, that is, the pressure of the air that surrounds us (approximately 1 bar); submarine pressure, which increases by 1 bar for every 10 m (33 ft) you go down; car tire pressure (2 bar); public works water pressure (3 bar), etc.