The traditional nine-bar pump pressure standard for espresso machines is facing growing scrutiny among coffee specialists, who argue that the rigid benchmark often harms light-roast beans and overlooks modern technological alternatives.
While some manufacturers of portafilter machines still market 15 bar, the actual pressure at the pressed coffee in the filter is nine bar for nearly all espresso machines. The figure echoes a mechanical convention established in the 1940s.
Roots in Mid-Century Muscle Power
The persistence of the nine-bar benchmark stems directly from mid-20th-century engineering constraints rather than absolute flavor optimization.
In the 1940s, Achille Gaggia implemented this specific pressure level in lever machines to ensure users could still push the spring in the piston down with their muscle power. Coffee expert Lance Hendrick highlights that Faema later simply adopted the nine-bar pressure for its E61 brew group even when a different pressure would have been technically possible. Consequently, this historical figure became entrenched across nearly all standard portafilter machines.
The Light-Roast Extraction Problem
While some beans yield an excellent espresso under standard nine-bar extraction, lighter roasts often react poorly to identical conditions.
Lightly roasted coffee beans demand different handling to properly dissolve fruit acids, sugars, and aromatic compounds. Advice online increasingly suggests dialing extraction down to six bars or adjusting pressure during the extraction to improve the result, particularly when playing with the saturation of the puck as the extraction starts.
Shifting to Flow Rate and Software
To break away from static pressure limitations, contemporary equipment manufacturers utilize internal sensors and software that prioritize a different metric altogether: flow rate, measured in milliliters per second.
Modern machines such as the Decent, Maro, Roxy, and Zuriga allow users to define brew profiles dictating how much hot water passes through the puck per second. Because the coffee behaves differently during extraction and the grind size is variable, the internal pump continuously adjusts its pressure—frequently dropping below the traditional nine-bar threshold—to maintain the flow rate.
