Hot Beverage Technology
Brew pressure
Term from the vending glossary
Water pressure as it flows through the coffee puck in the brew group; 9 bar is the espresso standard. Excessive pressure (>10 bar) produces bitter over-extraction; insufficient pressure (<7 bar) produces weak, acidic under-extraction. In vending machines, brew pressure is fixed; on commercial-grade machines, it is adjustable.
Brew pressure is the force with which water is pushed through the coffee grounds. For espresso, approximately 9 bar has become the standard reference; below that, extraction becomes thin and weak; significantly above it, the drink tastes bitter because undesired compounds dissolve alongside the flavor compounds.
On a vending machine, the pressure setting tells only part of the story. What ultimately reaches the cup also depends on grind size, the amount of coffee grounds, and water temperature — three variables that can compensate for one another. Selecting a machine based solely on its pressure specification therefore means comparing a technical parameter, not an actual result.