Why is the extraction pressure of espresso 9bar? What does it have to do with the extraction parameters and how to adjust it?

Front Street Coffee often says that a good espresso is easy to get (exaggerating) once we understand the relationship between the extraction parameters of espresso coffee, and these extraction parameters are grinding degree, powder amount, powder/liquid ratio, and extraction time.

But do you know that there is another parameter that is actually more important, but it is more troublesome for some coffee machines to adjust, so the main mention of Qianjie Coffee is the above extraction parameters that are easy to control. So, today! Front Street Coffee wants to share this extracted "hidden minister"-"extraction pressure"!

The golden Crema is what sets espresso apart from regular coffee, because only pressure extraction can produce this dense, thick foam.

Usually, people's impression of the pressure of the coffee machine is almost "9bar", which is largely related to the various Italian teaching methods that are usually searched! Of course, this is true, the coffee machine pressure setting in the factory default is mostly 9bar. So, the question is: do you know why the default pressure of the coffee machine is set at 9bar?

First of all, let's first understand the pressure difference of the coffee machine, the pressure of the coffee machine is divided into extraction pressure and pump pressure! Extraction pressure: As we often refer to 9bar, it refers to "extraction pressure"! That is, when we screw on the handle, to extract the substances in the coffee when the pressure exerted, this is the extraction pressure! Pump pressure: The extraction pressure of the coffee machine is derived from the booster pump in the machine. The pump pressure refers to the pressure directly provided by the booster pump when the extraction key is opened. It and extraction pressure each have a dial, when we just give the coffee machine water, not buckled with any items that need to apply pressure, there will be a dial pointer when pressing the extraction key directly rotating, it is "pump pressure gauge."

And when you buckle the handle with a powder cake, or when the non-porous handle is extracted, the index of a dial will gradually increase after the water is discharged, then it means that it is an "extraction pressure gauge"!

All right! To clarify the difference between the two pressures, let us understand why the extraction pressure of coffee machines is generally 9bar!

Why is the extraction pressure standard for coffee machines at 9bar? To know more clearly why 9bar is used as the standard, we can conduct an extraction experiment to intuitively understand what changes the concentration parameters will have under different pressures! The amount of powder used in this extraction experiment is 20g, and the ratio of powder to liquid is 1:2, that is, 40ml. This is a parameter set by Qianjie Coffee on the basis of 9bar! Under the standard pressure of 9bar, the extraction time of 40ml coffee solution from 20g coffee powder is 30 seconds, and the flow rate per second is in the range of 1.4~1.6!

Then let's use 6bar and 11 bar to see how long they take and what difference they make in taste! When the pressure is adjusted to 6bar for extraction, the extraction pressure gauge can see a large change. Originally, when extracting at 9bar, it took only 5~6 seconds from 0 to 9bar, but after adjusting to 6bar, it took 7 seconds from 0 to 6bar, and the flow rate was slower (0.7~0.9ml per second). It took 38 seconds to extract 40ml of coffee from 20g of coffee powder.

Finally, the 11 bar pressure test! Through the pressure gauge we can see that the time required from 0 to 11 bar is 5 seconds, the initial flow rate is no different from 9bar, but with the advancement of time, the faster the extraction! In the end, it used an extraction time of 27 seconds and a flow rate of 1.5 to 1.8 per second!

After extraction, Qianjie coffee was tasted in time, and the result was as follows: the concentrate extracted from 6bar did not look much different from the concentrate extracted from 9bar in appearance, but the taste of oil would be rough, and its sour aroma was not too rich compared to 9bar, and the layering was not obvious enough. However, it will taste softer and more mellow; 11 bar concentrated similarly, the appearance does not look much different, but through the taste will find that its acid fragrance will be more prominent, rich, and even to the point of stimulation!

Although this is a parameter set on the basis of 9bar, we can also intuitively understand that under the same parameters (grinding, powder amount, powder-water ratio), the lower the extraction pressure, the longer the extraction time, the flavor level will not be so obvious, and the taste will be softer; and the higher the extraction pressure, the shorter the extraction time, and the taste will be more impactful! This is actually related to the sweet, sour and bitter extraction formula often mentioned in Qianjie Coffee, but that is not the focus of today ~

Having said that, the reason why 9bar will be used as the current coffee machine pressure standard is because after the popularity of the coffee machine with the pump supercharged, it completely replaced the coffee machine with only 3~4bar in the ancient time. After all, the new coffee machine has a higher extraction pressure and can extract coffee more quickly, but the problem also arises. It was found that it was not the higher the pressure, the faster the speed, the better the coffee extracted. When the pressure is higher than 10bar, the coffee extracted easily has a charcoal-like burnt wood taste. However, at 9bar, negative conditions were the least common, and the coffee came out with a good taste and flavor. Therefore, the advantages of 9bar are slowly becoming the default pressure of the coffee machine under everyone's praise!

Just like the previous article of Qianjie Coffee said, with the development of the times, the pressure during extraction is no longer just the same 9bar. In the concentrated extraction time can be artificially adjusted, so that the pressure changes, so that the espresso can present their desired taste, this extraction method has a professional term-"pressure swing extraction." When I have time in the future, Front Street Coffee will come back and say ~

- END -

Front Street Cafe

No.10 Baoanqian Street, Yandun Road, Dongshankou, Yuexiu District, Guangzhou City, Guangdong Province