Espresso Pressure Profiling: Is 9 Bar Right?
What pressure profiling is, where 9 bar comes from, and what blind tests at 6, 9 and 12 bar found. Includes a test plan for your own machine.
Where the evidence stands. Most espresso machines pull at about 9 bar, and that figure is a convention rather than a law of coffee.
Key takeaways
- A normal pump machine pushes water at a fixed pressure from the first second to the last.
- We found no peer-reviewed study that controls for roast, dose and grind while varying pressure.
- Seven Miles found TDS tracked extraction time more than pressure, and Climpson found extraction percentage did not follow pressure.
- Do I need a machine with profiling? No. A good grinder and a consistent dose change the cup more.
- A gentle start can help, but poor puck prep causes channeling.
Pressure profiling means changing pressure during the shot, typically a gentle low-pressure start, a hold, then a decline. The published evidence is thin and mixed: one cafe's blind tasting preferred 6 bar to 9, another's found 6 bar watery, so test on your own coffee rather than copy a profile.
What pressure profiling is
A normal pump machine pushes water at a fixed pressure from the first second to the last. A profile varies it. The stages people talk about are:
- Pre-infusion: low pressure or flow at the start, to wet the puck before the full load arrives.
- Ramp: the rise from pre-infusion to the main pressure.
- Hold: the main pressure, usually near 9 bar.
- Decline: a drop in the last stretch, which is how a spring lever machine behaves naturally.
Pressure and flow are tied together through the puck. Fines in the bed reduce permeability, slow the flow and lengthen the shot, a point shown in a 2024 Scientific Reports study. On many machines you set flow and the puck sets the pressure.
Where 9 bar comes from
- Lever machines: Achille Gaggia's piston machine of the mid-1940s used a spring that delivered about 8 to 10 bar, falling as the spring relaxed.
- Pump machines: the Faema E61 introduced the pump-driven machine in 1961, which made a steady 9 bar easy.
- Industry standard: the Italian Espresso National Institute describes an espresso as about 7 g of coffee, 88°C water, 9 ± 1 bar, around 25 seconds and 25 ml in the cup. It is an industry association's specification, not a law.
So 9 bar is a sensible default that machines settled on, not a number coffee demands. The question is whether anything else tastes better.
What the tests found
We found no peer-reviewed study that controls for roast, dose and grind while varying pressure. What exists:
| Test | What was compared | Result |
|---|---|---|
| Climpson & Sons | Two identical machines, one at 6 bar and one at 9 bar; blind staff tasting after each was dialled in | Lower pressure won for espresso and milk drinks; described as sweeter and more balanced. Extraction percentages did not track pressure; all sat within 18 to 22% |
| Seven Miles | La Marzocco Linea machines at 6, 9 and 12 bar, 14 g, 17 g and 21 g doses | 6 bar was watery and thin even after finer grinds and higher doses; 12 bar was mixed, with some liking the body; they kept 9 bar. TDS tracked extraction time more than pressure |
| Decent Espresso | Flat 9 bar vs a lever-style decline vs a profiled shot | The maker's demo favoured a profile that ends at a lower pressure than flat 9 bar. It is a demonstration on one roast, not a controlled test |
| Flair 58 manual | Hand-operated lever with a pressure gauge | The manual suggests aiming for 6 to 10 bar and 30 to 35 seconds when starting |
Read this as a split decision. Climpson and Seven Miles disagree about 6 bar, and each used different coffee, machines and tasters. Seven Miles also noted that its blends may have been designed around 9 bar, and that higher pressure lengthened extraction on fresh coffee, possibly because of trapped CO2.
What it means for you
- Change one thing at a time. Pressure, grind and dose interact, because pressure moves flow and flow moves time.
- Pre-infusion is the easiest change to try. It needs no new gear on machines that offer it, and it has the clearest mechanical logic: a more even wet-up of the puck.
- A decline in the final third mimics a lever. Climpson's tasters called lower pressure sweeter, and a decline is the way to get some of that without lowering the whole shot.
- Lower pressure may suit darker roasts and higher pressure lighter ones. Seven Miles floated this and left it for later testing; treat it as a hypothesis.
A test plan
Use the same coffee, dose and yield for every shot. Keep a note of time and taste.
- Baseline: your machine's fixed 9 bar. Record the time and the taste.
- Pre-infusion: add 5 to 10 seconds of low pressure or flow before the main push.
- Decline: hold 9 bar for two-thirds of the shot, then let it fall toward 6 bar. A lever machine does this by itself.
- Lower flat pressure: if you can set a flat 6 or 7 bar, pull it, expecting a longer or finer-ground shot to compensate.
- Taste each shot blind if someone can pour for you. Keep a profile only if you prefer it two times out of three.
These test points are chosen from the 6 to 12 bar range the sources report. They are not validated optima.
What your machine can do
- Fixed pressure: most entry-level pumps. You can only change dose, grind and yield.
- Adjustable pressure valve: some machines let you set the pump limit.
- Flow control: a paddle or valve controls how fast water enters the group, and pressure follows. Lelit's Bianca uses a paddle.
- Fully programmable: machines such as the Decent DE1 let you draw the whole curve.
- Manual lever with gauge: you supply the pressure by hand and watch the gauge.
What people ask about profiling
Is 9 bar the best pressure for espresso?
It is the common default and the safest starting point. Whether lower or higher gives a better cup depends on the coffee, the roast and your taste, and the tests we found do not agree.
Does higher pressure extract more?
Not reliably. Seven Miles found TDS tracked extraction time more than pressure, and Climpson found extraction percentage did not follow pressure.
Is pre-infusion worth using?
Usually yes if your machine has it. It wets the puck evenly before the main push, which is the logic behind it.
Do I need a machine with profiling?
No. A good grinder and a consistent dose change the cup more. See our burr grinder guide.
Will profiling fix channeling?
A gentle start can help, but poor puck prep causes channeling. Fix distribution first.
Related
Sources
- Climpson & Sons: 9 bar vs 6 bar espresso.
- Seven Miles: espresso pressure.
- Decent Espresso: how pressure profiling changes flavor (manufacturer).
- Smrke S, Eiermann A, Yeretzian C. The role of fines in espresso extraction dynamics. Scientific Reports 2024. doi:10.1038/s41598-024-55831-x
- Espresso machine, Wikipedia for lever pressure and the E61.
- The Italian Espresso National Institute specification as reproduced by Philips and Coffee Crew.
- Flair 58 user manual.