Almost everybody who is looking to buy an espresso machine has been told that a machine with a 17 bar pump makes better espresso than a machine with a 15 bar pump. It was the old thought process of “if big is good, bigger is better,” and I hear it all the time. There is nothing farther from the truth, so by choosing a machine by the size of its pump you may be directed away from the perfect one that would fit nicely for your lifestyle. Up until recently, just about every commercial espresso machine was set to brew at 9 bars and only a very few brew at higher or variable pressure. In this blog I’m not going to go into the science on how the pressure affects the whole brewing process, we will assume that the Italian engineers, who have been doing it for generations, have it right.
What is “Bar” Pressure?
1 bar = 14.5 pounds per square inch (psi), which means that with a brew pressure of 9 bar we are actually brewing at 130 PSI — and that is a lot of pressure. To put it into perspective, consider that standard car tires hold about 35 PSI.
If We Have a 15 Bar Pump, How Can We Brew At a Lower Pressure?
All good quality machines with vibration pumps will have a valve that reduces the brew pressure by diverting the excess pressure over 9 bar either back into the reservoir, inlet side of the pump, or to the drip tray. These valves are known as an OPV (over pressure valve) valve and they come in different sizes and shapes. They also act as safety valves to relieve excess pressure in the event that a boiler overheats.
When purchasing an espresso machine from a company that has history in espresso, you can trust the engineers who designed the machine. When they choose a pump they know how much pressure is required to pump the water at the proper quantity and velocity through the boiler system that they have chosen. Then they control it with the proper OPV for the style of machine that fits the customer that the machine is designed for. So if the pump is rated for 15 bar or over, there is no need to worry. Sounds complex? Not really, just trust that they did it right and focus on picking the type of machine that fits your lifestyle, wants, and desires. That’s what I would do.