9 Bar Pressure: The Gold Standard
When it comes to the question of pressure, we’re often presented with a false dichotomy, where on the one hand, we’re told that 9 bar pressure is the industry standard for pulling espresso shots. On the other hand, pressure profiling is the only way to unlock the deep mysteries of any given espresso bean. In reality, what initially seems like a rigid binary is a more fluid and rich continuum.
*Disclaimer* Espresso shots can taste great at different pressures, which we cover in Flow Control: Your Questions Answered and All Things Flow Control.
What are BARS?
To keep it simple, nine-bar pressure refers to a unit of measurement used to describe the amount of force used to extract espresso. One bar equals atmospheric sea-level pressure, approximately 14.5 pounds per square inch (psi) or 100 kilopascals (kPa).
A Short History Lesson
Before there were pump-driven and spring-lever machines, we relied upon machines that used steam pressure to extract espresso at 1-2 bar pressure at the group head. These steam-powered shots were watery and bitter, which was the case at the 1906 Milan World’s Fair when “espresso” debuted. While these primitive espresso machines by Bezzera and Pavoni innovated the speed at which you can produce coffee, they did not resemble the crema-laden espresso we know and love today. Not enough pressure = no crema. The following points are not an exhaustive list of innovations but are a few of the most important ones.
- The next major innovation was in the 1940s when Achille Gaggia introduced a spring-powered piston to quickly force hot water through coffee grounds and produce a concentrated beverage, creating a rich, creamy layer on top of the drink we now call crema. The lever machine significantly improved the efficiency of the espresso-making process and helped popularize the drink in Italy.
- Lever machines were roughly a decade's standard configuration for espresso machines until Ernesto Valente introduced the Faema E61 espresso machine in 1961. The E61 mechanically pumps water through the coffee bed at 9 bars of pressure. These machines were driven by an electric pump, which made it much easier to achieve consistent pressure for each shot in the café setting. Almost all semi-automatic and automatic espresso machines today are pump driven and can achieve 9 bar pressure.
What is This Doing to my Coffee?
We’d be stuck in the espresso doldrums without the pump-driven machine. The home espresso machine as we know it would be less accessible to everyday folks passionate about the craft of espresso-making at home. More importantly, coffee would taste worse. The key takeaways are that temperature and 9 bar pressure tend to produce better and more consistent espresso outcomes.
Beware of 15 and 18 Bar Promises
More bars make for a better product, right? Not really. Manufacturers advertise this on machines with low build quality and use inferior parts. Fifteen bars of pressure is way too high to brew for espresso and would result in some unsatisfactory extractions. Semi-automatic espresso machines, especially ones that employ vibratory pumps, will also use an expansion valve or OPV to regulate this pressure at the group head down to 9 bar. Consistency and control are critical.
One thing we can depend on with pump-driven machines is that, generally, pressure is something that, while important, is more or less in the background. This will help you focus on other variables, such as altering your grind size and building an espresso recipe. Happy shot pulling!