For decades, "9 bars" was the law. You pushed a button, the pump slammed onto the puck at 9 bars, and it stayed there until you stopped. But the best espresso in Italy was arguably made on spring levers—machines that did something very different.
What is Flow/Pressure Profiling?
It is the ability to change the pressure (or flow rate) of the water during the shot. Instead of a flat line (9 bars all the way), you can create curves.
The "Spring Lever" Profile (Declining Pressure)
This is the Holy Grail profile that modern machines like the Decent DE1, Slayer, and Lelit Bianca try to emulate.
- Low Pressure Pre-Infusion: Gently wet the puck.
- Peak Pressure (8-9 bars): Ramp up to extract the acids, sugars, and oils.
- Declining Pressure (Taper to 4-6 bars): As the puck erodes, flow resistance drops. If you keep pushing 9 bars, you'll extract bad, astringent compounds. By lowering the pressure at the end, you maintain a steady flow and avoid bitterness.
Why Decline at the End?
Think of the coffee puck like a sugar cube. At the start, it's solid and resistant. By the end of the shot, much of it has dissolved. The puck is weaker. Hitting a weak puck with high pressure causes "channeling" and washes out tannins (dry, woody flavors).
Tapering the pressure saves the finish of your shot. It keeps the body thick and the aftertaste sweet rather than harsh.
How to Do It
1. The Slayer Shot (High Flow Restriction)
Machines like the Slayer use a needle valve to restrict flow dramatically for a long, slow pre-infusion, allowing you to grind ultra-fine.
2. E61 Flow Control Kits
You can retrofit many production machines (Profitec, Rocket, Lelit) with a flow control mushroom. This adds a paddle to the top of the group head.
- Start: Paddle open a tiny bit (2g/s flow).
- Middle: Paddle open wide (9 bars).
- End: Slowly close the paddle to drop pressure as the shot blondes.
3. "Saving" a Shot
Flow control is also a rescue tool. If you ground too coarse and the shot is running fast, you can restrict the flow to slow it down and still get a decent extraction. If you ground too fine and it's choking, you can open the flow to force it through.