Why Use 9 Bar for Espresso? How Does Pressure Affect Espresso?

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Introduction

As everyone knows, espresso is the foundation of Italian coffee. The taste of Italian coffee is influenced by espresso to some extent. Good Italian coffee often requires a properly extracted espresso base, making the importance of espresso self-evident.

The steps to make espresso are actually quite simple, but there are many details to pay attention to during preparation. First, ensure that the coffee beans are fresh enough and fully rested. The first step is to remove the portafilter and wipe the filter basket clean. The second step is to grind the coffee beans and let the coffee grounds fall into the portafilter's filter basket. The third step is distribution and tamping. The fourth step is to lock the portafilter for extraction. Finally, end the extraction, remove the portafilter and clean it.

While it may seem simple, there are many details to pay attention to. Before receiving the grounds, ensure the filter basket is clean and dry. When receiving and distributing the grounds, try to make the coffee grounds evenly distributed in the filter basket as much as possible. When tamping, the force should be vertical downward, and the tamping force should be consistent each time. Therefore, learning to make a cup of espresso is not difficult, but making a good espresso and making every espresso well requires more learning and practice.

But today, FrontStreet Coffee wants to share not just about espresso, but also a major element of espresso - the pressure during espresso extraction.

The Characteristic of Espresso - Pressurized Extraction

Common pour-over coffee, such as coffee brewed with a V60 dripper, we generally classify as drip extraction. For methods like French press and cupping, we call them immersion extraction. Drip extraction relies on the flow of water to extract coffee substances, while immersion extraction relies on soaking to directly extract coffee flavors. However, espresso is difficult to classify into the above two categories. Compared to most brewing methods, the biggest characteristic of espresso lies in the pressure during extraction.

When making espresso, the coffee grounds in the portafilter's filter basket are extracted under 9 bar pressure. Substances in the coffee grounds are quickly dissolved under pressure, so espresso extraction time is very short. Pour-over coffee typically takes 2 to 3 minutes on average, while espresso can complete extraction mostly between 20 to 30 seconds. This extraction method also leads us to classify espresso as "pressurized extraction."

Espresso machines mainly rely on pumps to provide pressure, divided into two main types: vibratory pumps and rotary pumps. Vibratory pumps generate pressure through high-speed repeated vibrations of a piston-like structure. The disadvantages are loud noise, short lifespan, and gradually increasing pressure, making it impossible to ensure stable pressure at 9 bar throughout the entire extraction process.

Rotary pumps, on the other hand, generate pressure through high-speed rotation of metal vanes. Compared to vibratory pumps, they eliminate reciprocating motion, have less noise, longer lifespan, and provide pressure in one step. Therefore, commercial coffee machines generally use rotary pumps mainly, with better stability for continuous cup production.

The Product of Pressure - Crema

Because of pressure, espresso also has an attractive layer of oils in appearance. During the extraction process, hot water passes through the coffee puck. Due to excessive pressure, the carbon dioxide in the coffee grounds becomes supersaturated in water. The carbon dioxide cannot be released and directly integrates into the coffee liquid. The high-pressure environment also forces the fats contained in the coffee to separate from the coffee puck, thus being carried out by the hot water.

After extraction ends, the coffee liquid flows from the machine, and atmospheric pressure returns to normal. At this time, the carbon dioxide still remaining in the coffee liquid is ready to return to the air, but during this process, it encounters the fats in the coffee liquid. The fats envelop the carbon dioxide and float on the surface of the coffee liquid. This is how this layer of crema is produced.

Espresso crema is mainly influenced by several factors: the freshness of coffee beans, the roast degree of coffee beans, and the extraction degree of coffee beans. The fresher the coffee beans, the more carbon dioxide content, and the richer the crema. Similarly, the deeper the roast degree, the richer the crema will also be.

In addition to these, espresso crema is also affected by the pressure of the espresso machine. The production of crema mainly relies on the high-pressure extraction environment. Insufficient pressure will reduce the extraction of fats from the coffee beans, naturally resulting in less crema.

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