The Pressure Paradox: Why "20 Bar" is a Physics Lesson, Not a Feature

In the crowded market of entry-level espresso machines, a number often screams from the box: 20 Bar Pressure. The FOHERE CM5418-UL is no exception. To the uninitiated, this sounds like “more is better.” If 9 bars make good espresso, surely 20 bars make it twice as good?

The reality is a lesson in fluid dynamics. In professional espresso extraction, 9 bars is the “Goldilocks” zone. It creates enough force to emulsify oils into crema without compressing the coffee puck so hard that water cannot pass through.

So why do machines like the FOHERE advertise 20 bars? It comes down to the type of pump used: the Vibration Pump.

The Vibration Pump vs. The Puck

Commercial machines use Rotary Pumps, which deliver constant pressure instantly. Home machines use Vibration Pumps, which operate on a piston oscillating inside a magnetic coil. The “20 Bar” rating is the pump’s static limit—how hard it can push against a complete blockage.

However, coffee brewing is dynamic. As water flows through the coffee grounds, pressure drops. The actual pressure at the group head is determined by the Hydraulic Resistance of the coffee puck. * Too Coarse: Water flows fast, pressure stays low (sour, weak coffee). * Too Fine: Water is blocked, pressure climbs towards 20 bars.

At 20 bars, strange things happen. The coffee puck compresses into a solid brick. Water, unable to pass through evenly, blasts a hole through the weakest point. This is Channeling. The result is a shot that is simultaneously bitter (from the channel) and sour (from the rest of the puck).

Taming the Beast: The Role of the OPV

High-end machines use an Over-Pressure Valve (OPV) to bleed off excess pressure, capping it at 9 bars. Budget machines often lack this expensive component.

Does this mean the FOHERE is flawed? Not necessarily. It means the user must become the regulator. By carefully adjusting the Grind Size and Tamp Pressure, you are manually tuning the resistance of the puck. You are aiming for a grind that allows water to flow at a rate that naturally generates about 9 bars of back-pressure, without triggering the pump’s maximum 20-bar output.

The Safety Net: Pressurized Baskets

To help beginners, FOHERE includes Pressurized Filter Baskets. These baskets have a single tiny hole on the bottom. This artificial restriction creates the necessary back-pressure regardless of your grind size. It forces the coffee to foam, creating a “faux crema.”

While purists scoff, from a physics standpoint, this is a brilliant solution. It guarantees a consistent extraction pressure even if your grinder isn’t capable of espresso-fine precision. It democratizes the physics of espresso, making it accessible without a $500 grinder.

Conclusion: You Are the Engineer

The FOHERE CM5418-UL is a tool that invites you to understand the relationship between flow, resistance, and pressure. The “20 Bar” label is a reminder of the power at your disposal. Your challenge is to harness that power, using the physics of the puck to tame the pump and extract liquid gold.