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What is the concept of 9 bar in an espresso machine? How much pressure should be applied when tamping coffee grounds for espresso?

Published: 2026-01-27 Author: FrontStreet Coffee

Last Updated: 2026/01/27, FrontStreet Coffee shared in the article 'The Importance of Distribution and Tamping' that in the preparation steps before espresso extraction, whether the coffee grounds are evenly distributed in the portafilter and whether force is applied evenly during tamping will affect the extraction and influence the taste of espresso. However, since it didn't mention the amount of force that should be used for tamping, many people

In the article "The Importance of Distribution and Tamping," FrontStreet Coffee shared that in the preparation stages before espresso extraction, whether the coffee grounds are evenly distributed in the portafilter and whether force is applied evenly during tamping will both affect the extraction and influence the taste of the espresso. However, since the article didn't mention how much force should be used for tamping, many friends have privately messaged FrontStreet Coffee: How much force should be used for tamping?

In fact, FrontStreet Coffee has previously shared several articles about tamping force tests, but because these articles only contained experimental comparisons, we believe many friends couldn't fully understand them. Therefore, today FrontStreet Coffee will focus on sharing: the impact of tamping force on extraction, and what exactly the concept of 9bar pressure from a coffee machine means. Why mention the coffee machine's pressure? You'll understand as you read on!

Extraction Experiment

So first, let's get straight to the point and see what changes occur in extraction time and espresso taste when using the same amount of coffee grounds with different tamping forces. We used 20g of coffee grounds, with a target extraction weight of 40ml, and tamping forces of 2kg for light tamping (just a light press) and 18kg for heavy tamping (a firm press). To ensure stable results, FrontStreet Coffee extracted a total of 6 espressos and took the average extraction time, with the following results:

The three espressos using 2kg light tamping averaged: 33 seconds. The three espressos using 18kg heavy tamping averaged: 34 seconds. In terms of flavor, there was almost no significant difference between the two: balanced sweet, sour, and bitter notes, with prominent flavors. But the story doesn't end here. FrontStreet Coffee then extracted two more special espressos. What made them special?

The special thing about these two espressos is that they were extracted directly without being tamped after distribution. And their extraction results were similar, taking 33 seconds (as for the taste... we'll discuss that later). From the extraction times, we can see that whether using light tamping, heavy tamping, or no tamping at all, the extraction time didn't show significant changes.

This might differ from most friends' understanding. FrontStreet Coffee once believed that when we use greater tamping force, the coffee grounds can be compacted more tightly, and extraction time would be relatively extended due to increased resistance from the coffee puck, thereby improving extraction efficiency. In reality, this is not the case. The reason is simple because many people overlook the extraction method of coffee machines.

How Strong is the Coffee Machine's Extraction Pressure?

As we all know, espresso machines use pressurization to quickly produce a cup of coffee in a short amount of time. Generally, during the espresso extraction process, the coffee machine will use 9 standard atmospheres of pressure for extraction, which is what we commonly refer to as 9bar (normally fluctuating between 7-12).

Perhaps because the number is a single digit, many friends cannot comprehend how strong this force actually is. That's okay - let's do a simple conversion: 1bar from a coffee machine applied to a puck in a 58mm portafilter equals approximately 27kg of force, so 9bar would be 27*9 = about 243kg, which is equivalent to the weight of 4 adults. One can imagine why coffee machines can extract substances from coffee so quickly. Therefore, we can understand that no matter how hard we tamp, it's insignificant in the face of 9bar pressure. But this raises another question: why do we need to tamp at all? If tamping is ineffective, wouldn't it be better to just extract directly after distribution?

Why Do We Need to Tamp?

This question is actually quite simple because we need to reduce channeling effects. As the saying goes: water flows downward. Because water has inertia, it will flow to places where it can move easily. The same principle applies during extraction! Without tamping, there will be many gaps between coffee grounds. These gaps will allow hot water to concentrate and pass through during extraction, causing uneven extraction.

The reason FrontStreet Coffee didn't share the taste experience from the untamped extraction above is because the uneven extraction resulted in negative flavor characteristics. Therefore, we need to eliminate gaps as much as possible through appropriate tamping to allow hot water to extract more evenly. The force doesn't need to be excessive - moderate is sufficient (press the tamper down to the bottom).

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