Nav: Home > Coffee >

Why Espresso Machines Use 9 Bar Pressure to Extract Coffee

Published: 2026-01-28 Author: FrontStreet Coffee

Last Updated: 2026/01/28, When FrontStreet Coffee shares knowledge about extracting espresso, we often discuss the extraction relationship between dose, ratio, grind size, and time. Once you master these 4 parameters, you can skillfully operate an espresso machine. However, there's another parameter that's often glossed over but is actually the most critical to espresso extraction

For more premium coffee knowledge, please follow the WeChat official account: FrontStreet Coffee

The Critical Role of Pressure in Espresso Extraction

When FrontStreet Coffee shares knowledge about espresso extraction, we frequently discuss the extraction relationships between dose, ratio, grind size, and time. Mastering these four parameters allows for flexible operation of an espresso machine. However, there's another parameter that's often briefly mentioned but is actually the most critical factor in espresso extraction: pressure.

We know that espresso extraction differs from other brewing methods in that it uses pressure, while others operate under normal pressure. Pressurized extraction can more easily produce rich coffee, and that golden crema can only be created through pressure.

In various espresso extraction tutorials and coffee machine manuals, the extraction pressure for espresso is always 9bar, as if "espresso extraction pressure = 9bar" is a truth etched into everyone's memory. So why does everyone use 9bar as the standard?

Understanding Pump Pressure vs. Extraction Pressure

FrontStreet Coffee will first explain a concept: pressure is divided into pump pressure and extraction pressure. The 9bar pressure we refer to is the extraction pressure. You can observe the pressure gauge - if it starts moving when you turn on the button, it represents pump pressure. If you turn on the button without attaching the portafilter and the pressure gauge doesn't respond, but when you add coffee grounds and attach the portafilter then turn on the button and the pressure gauge starts moving, this indicates it's measuring extraction pressure.

Types of Espresso Machine Pumps

The pressure source for espresso machines mainly relies on pressure pumps within the machine body. Currently, machines on the market are mainly divided into two types of pressure generation: vibration pumps and rotary pumps. Vibration pumps generate pressure through high-speed repeated vibrations of a piston-like structure, making it difficult to maintain stable pressure within just 30 seconds. These pumps are typically set at 15bar pressure, but might slowly climb to 15bar initially, then rapidly decrease below 9bar. Some home machines have lower water flow, causing extraction pressure to be lower than pump pressure.

Rotary pumps generate pressure through high-speed rotation of metal plates, providing fast pressure response and more stable pressure. They are generally used in commercial machines and high-end home machines, where pump pressure and extraction pressure are basically consistent.

Pressure Experiment: Different Bars, Different Results

Since we want to understand why 9bar is used as the standard, let's conduct a small experiment to see how espresso performs under different pressures. FrontStreet Coffee uses a rotary pump machine, which can guarantee stable pressure during extraction. The parameters are based on 9bar settings: under standard 9bar pressure extraction, 20g of coffee grounds extracts 40g of espresso in 29 seconds.

Extraction at 6bar

Then FrontStreet Coffee used the same parameters but adjusted the pressure to 6bar for extraction. Through the pressure gauge on the group head, it took 7 seconds to go from 0bar to 6bar (normally 9bar extraction takes 5-6 seconds to go from 0-9bar). The overall flow rate was slower compared to 9bar, and the final time to extract 40g of espresso was 36 seconds.

In terms of crema richness, it was comparable to 9bar, but the crema was coarser and dissipated faster than the 9bar version. Tasting comparison showed that the espresso extracted at 6bar was less rich in aroma and acidity, with a softer, heavier profile.

Extraction at 11bar

Next, the pressure was adjusted to 11bar. Through the pressure gauge, it took 5 seconds to go from 0-11bar. The initial flow rate was similar to 9bar, but as time went on, it became slightly faster than 9bar, with a final time of 27 seconds.

There wasn't much difference in the crema. Through tasting, the 11bar espresso was more intense and rich than the 9bar version.

FrontStreet Coffee conducted this comparison to demonstrate that when pressure is lower, extraction time becomes longer, crema performance is inferior, and the flavor becomes more "mild." When pressure is higher, extraction time is shorter, and the flavor becomes richer and more intense.

The Historical Origin of 9bar Standard

The reason 9bar became the standard for espresso extraction dates back to Italy in the 1960s and 1970s. At that time, pump-powered coffee machines were becoming popular, replacing the older 3-4bar machines. The new machines had higher pressure, but this brought a problem - higher pressure didn't necessarily mean better-tasting coffee. They discovered that using pressures above 9-10bar for extraction often produced burnt, woody flavors that were unpleasant. Gradually, everyone found that 9bar pressure extraction provided good performance in both richness and flavor profile, so 9bar became the default pressure for extracting espresso.

Modern Variable Pressure Extraction

With the popularization of variable pressure functions in modern coffee machines, more and more people are using variable pressure extraction - manually changing extraction pressure to balance coffee flavor compounds. Full 9bar extraction is no longer the only standard for extracting concentrated coffee.