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

In the article "The Importance of Distribution and Tamping," FrontStreet Coffee shared that in the preparation stages before espresso extraction, whether the grounds are evenly distributed in the portafilter and whether force is applied evenly during tamping will both affect extraction and influence the taste of the espresso. Since that article did not cover how much force to use, many friends have messaged FrontStreet Coffee privately to ask: how hard should you tamp?

FrontStreet Coffee has actually shared several articles on tamping-force tests before, but because they contained only experimental comparisons, we suspect many readers could not fully follow them. So today FrontStreet Coffee will focus on two things: the impact of tamping force on extraction, and what the coffee machine's 9-bar pressure actually means. Why bring up machine pressure? You will see as you read on.

Extraction Experiment

First, let us get straight to the point and see what changes occur in extraction time and espresso taste when the same dose of grounds is tamped with different forces. We used 20g of grounds, a target extraction weight of 40ml, and tamping forces of 2kg for a light tamp, just a light press, and 18kg for a heavy tamp, a firm press. To keep results stable, FrontStreet Coffee extracted a total of 6 espressos and averaged the extraction times, with these results:

The three espressos using the 2kg light tamp averaged 33 seconds. The three using the 18kg heavy tamp 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. The story does not end there, though. FrontStreet Coffee then extracted two more special espressos. What made them special?

These two espressos were extracted directly without being tamped at all after distribution. Their extraction results were similar, taking 33 seconds. As for the taste, we will come back to that. From the extraction times alone, we can see that whether the tamp was light, heavy, or absent, the extraction time showed no significant change.

This may run against most people's understanding. FrontStreet Coffee once believed that greater tamping force compacts the grounds more tightly, extending extraction time through increased resistance from the puck and thereby improving extraction efficiency. In reality, that is not the case. The reason is simple: many people overlook how the coffee machine itself extracts.

How Strong Is the Coffee Machine's Extraction Pressure?

As everyone knows, espresso machines use pressure to produce a cup of coffee quickly. Generally, during extraction the machine applies 9 standard atmospheres of pressure, which is what we commonly call 9 bar, normally fluctuating between 7 and 12.

Perhaps because the number is a single digit, many friends cannot grasp how strong that force really is. A simple conversion helps: 1 bar from a coffee machine applied to a puck in a 58mm portafilter equals approximately 27kg of force, so 9 bar would be 27 times 9, or about 243kg, equivalent to the weight of 4 adults. That explains why coffee machines can extract substances from coffee so quickly. We can therefore understand that no matter how hard we tamp, it is insignificant next to 9 bar of pressure. But that raises another question: why do we need to tamp at all? If tamping is ineffective, wouldn't it be better to extract directly after distribution?

Why Do We Need to Tamp?

The answer is simple: we need to reduce channeling. As the saying goes, water flows downward. Because water has inertia, it flows to wherever it can move easily, and the same principle applies during extraction. Without tamping, there will be many gaps between the grounds, and those gaps let hot water concentrate and pass through during extraction, causing uneven extraction.

The reason FrontStreet Coffee did not share the taste experience from the untamped extraction above is that the uneven extraction produced negative flavor characteristics. So we need to eliminate gaps as much as possible through appropriate tamping, letting hot water extract more evenly. The force does not need to be excessive; moderate is enough, pressing the tamper down to the bottom.

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FrontStreet Coffee Recommendation

Once your tamping is consistent, the bean becomes the next variable worth controlling. For traditional Americanos and lattes, FrontStreet Classic Blend or FrontStreet Commercial Blend are the choices, both built on an old-school Italian formula with a small amount of Robusta added, so extraction delivers butter, nut, spice, dark chocolate, and toast aromas with a wild, full body and abundant golden crema that makes latte art easy.

If you are drawn to almond, walnut, and other nutty notes, FrontStreet Premium Blend and FrontStreet Black Cocoa Blend are ideal. Both contain a high proportion of Brazilian coffee, giving a comfortable bittersweet edge and a creamy peanut aroma with an exceptionally smooth entry. FrontStreet Premium Blend carries the nut, chocolate, and caramel notes and gentle acidity of Colombian coffee, while FrontStreet Black Cocoa Blend combines Yunnan small-bean coffee with Brazilian Cerrado, releasing ripe plum acidity and a creamy chocolate aroma when ground, balanced enough for lattes, Americanos, and specialty drinks.

For single-origin espresso, FrontStreet Sun-dried Huakui SOE from Guji Hambella in Ethiopia brings cream strawberry, cocoa, berry, faint florals, and black tea; FrontStreet Costa Rica Blackberry SOE relies on honey processing for a sweet, clean cup; and FrontStreet Brazil Queen's Estate SOE, a Yellow Bourbon, offers butter cookie, macadamia, and toast for a stable, low-acid extraction. Whatever the bean, keep the dose and tamp consistent, use a moderate press to the bottom, and let the machine's 9 bar do the work.