Why is Espresso Extraction Pressure 9 Bar? How Does It Relate to Extraction Parameters and How to Adjust?

The Hidden Key Player: Understanding Extraction Pressure in Espresso

FrontStreet Coffee often says that once we understand the relationship between espresso extraction parameters, a delicious cup of espresso is practically effortless (slight exaggeration). These extraction parameters include grind size, dose, brew ratio, and extraction time.

But did you know that there's actually another parameter that's quite important? However, for some coffee machines, adjusting this parameter can be quite troublesome, which is why FrontStreet Coffee typically focuses on those easily controllable extraction parameters mentioned above. Therefore, today! FrontStreet Coffee is going to share this "hidden heavyweight" of extraction—extraction pressure!

The golden Crema obtained through pressure is what distinguishes espresso from regular coffee, because only pressurized extraction can produce this layer of dense, thick foam.

Typically, people's impression of coffee machine pressure is almost always "9bar," which largely relates to the various espresso tutorials commonly found online! Of course, this isn't wrong—coffee machines are generally set to 9bar as the default pressure at the factory. So, here comes the question: do you know why coffee machines have their default pressure set to 9bar?

Understanding Coffee Machine Pressure Differences

First, let's understand the different types of pressure in coffee machines. Coffee machine pressure is divided into extraction pressure and pump pressure!

Extraction Pressure: When we often mention 9bar, we're referring to "extraction pressure"! This is the pressure applied when we lock in the portafilter to extract substances from the coffee—this is extraction pressure!

Pump Pressure: The extraction pressure of a coffee machine comes from the pressure pump inside the machine. Pump pressure refers to the direct pressure provided by the pressure pump when the extraction button is activated. Both extraction pressure and pump pressure have their own gauges. When we're simply running water through the coffee machine without anything requiring pressure attached, there's a gauge pointer that moves directly when pressing the extraction button—that's the "pump pressure gauge."

When you lock in a portafilter with a coffee puck or use a bottomless portafilter for extraction, one gauge's reading will gradually increase after the water starts flowing, indicating it's the "extraction pressure gauge"!

Alright! Now that we understand the difference between these two types of pressure, let's explore why coffee machine extraction pressure is typically set at 9bar!

Why is 9bar the Standard for Coffee Machine Extraction Pressure?

To better understand why 9bar is used as the standard, we can conduct an extraction experiment to visually understand how espresso parameters change under different pressures! This extraction experiment uses a 20g dose with a 1:2 brew ratio (40ml), which is a parameter FrontStreet Coffee has set based on 9bar! At the standard 9bar pressure, extracting 40ml of espresso from 20g of coffee grounds takes 30 seconds, with a flow rate of 1.4-1.6ml per second!

Then we'll use 6bar and 11bar respectively to see how much time they take and what differences in flavor they produce! When the pressure is adjusted to 6bar for extraction, you can see significant changes on the extraction pressure gauge. Originally, with 9bar extraction, going from 0 to 9bar took only 5-6 seconds, but after adjusting to 6bar, going from 0 to 6bar takes 7 seconds, with a slower flow rate (0.7-0.9ml per second). Extracting 40ml of espresso from 20g of coffee grounds took 38 seconds.

Finally comes the 11bar pressure test! Through the pressure gauge, we can see that reaching 11bar from 0 takes 5 seconds. The initial flow rate is no different from 9bar, but as time progresses, it extracts faster and faster! Ultimately, it used 27 seconds for extraction, with a flow rate of 1.5-1.8ml per second!

After extraction, FrontStreet Coffee conducted immediate tastings, and here are the results: The 6bar extracted espresso looks similar to the 9bar espresso in appearance, but the crema tastes somewhat coarser, and its acidic aroma isn't as rich as the 9bar version, with less distinct layers. However, it tastes smoother and richer; The 11bar espresso similarly shows no significant difference in appearance, but through tasting, you'll find its acidic aroma is more prominent and intense, even reaching the point of being stimulating!

Although this experiment used parameters based on 9bar, it allows us to intuitively understand that under the same parameters (grind, dose, brew ratio), lower extraction pressure requires longer extraction time, with less distinct flavor layers and a smoother taste; while higher extraction pressure requires shorter extraction time, with a more impactful flavor! This actually relates to the sour-sweet-bitter extraction formula that FrontStreet Coffee often mentions, but that's not our focus today~

The History Behind 9bar as the Standard

Getting back to why 9bar became the current coffee machine pressure standard, it's because when pump-pressurized coffee machines became widespread, they completely replaced the early machines that only had 3-4bar pressure. After all, modern coffee machines have higher extraction pressure and can extract coffee more quickly, but this created problems! People discovered that higher pressure and faster speed don't necessarily produce better-tasting coffee. When pressure exceeds 10bar, the extracted coffee easily develops burnt wood flavors like charcoal. Then, when using 9bar pressure, negative conditions occur least frequently, and the resulting coffee tastes pleasant with good flavor performance. Thus, the advantages of 9bar were gradually passed around and slowly became the default pressure for coffee machines!

As FrontStreet Coffee mentioned in a recent article, with the development of our times, extraction pressure is no longer fixed at 9bar. During espresso extraction, pressure can be manually adjusted to create changes, allowing espresso to present desired flavors. This extraction method has a professional name—"variable pressure extraction." When time permits, FrontStreet Coffee will elaborate on this further~

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