What is the concept of 9bar for an espresso machine? How much pressure does it take to make espresso coffee?

Qianjie shared in the article "the importance of cloth and pressing Powder" that in the preparation before concentrated extraction, whether the coffee powder is evenly distributed in the powder bowl and whether there is a uniform force during filling will affect the extraction and affect the taste of espresso. But because there is no mention of the strength that the powder should use, so many friends are in the background private letter in front of the street: how much force should the powder use?

In fact, Qianjie has shared several test articles about the strength of powder pressing before, but because the article is only for experimental comparison, I believe many friends can not understand it very thoroughly. Therefore, today the front street will focus on sharing the effect of the force of pressed powder on the extraction, and what is the concept of the pressure 9bar of the coffee machine. Why mention the pressure of the coffee machine? Just look down and see!

Extraction experiment

So first of all, let's get to the point and take a look at how the same amount of powder changes in the time of extraction and concentration and the taste of espresso under different filling pressures. The amount of powder used is 20g, the target liquid weight of the extraction is 40ml, the filling pressure is light filling 2kg (that is, light pressure), and the heavy packing pressure is 18kg (that is, severe pressure). In order to ensure the stability of the results, Qianjie extracted a total of 6 concentrated parts, and then took the average extraction time, the results are as follows:

The average time for three servings of pressed powder lightly filled with 2kg was 33s. The average time of the three pressed powder refilled with 18kg was 34s. In the performance of the taste, there is almost no big difference between the two: the sweet and sour is balanced and the flavor is outstanding. But the matter is not over here, Qianjie then extracted two special concentrates, especially where?

What is special is that these two parts are not filled and pressed after the cloth powder is finished, but are extracted directly. And the result of their extraction is the same, the use time is 33s (as for taste. Talk about it later). We can see from the extraction time, whether it is light filling pressure, heavy packing pressure, or no packing pressure, the extraction time has not changed greatly.

This may be somewhat different from the understanding of most friends. Qianjie once believed that the greater the pressure of the powder we use, the tighter the powder can be pressed, and the extraction time will be relatively prolonged because of the increase in the resistance of pressed powder. As a result, the extraction efficiency is improved. In fact, this is not the case. The reason is simple, because many people ignore the way coffee machines are extracted.

How strong is the extraction pressure of the coffee machine? As we all know, the espresso machine uses a pressurized way to quickly make a cup of coffee in a short time. Generally speaking, in the concentrated extraction process, the coffee machine will use 9 standard atmospheric pressure for extraction, which is what we often call 9bar (normally fluctuates between 7 and 12).

Perhaps because the number is single digits, so many friends can not understand how big this force is, it doesn't matter, let's simply convert: the 1bar of the coffee machine applies about the force of 27kg on the pressed powder in a 58mm powder bowl, then 9bar is about 27*9=243kg, which is equivalent to the weight of four adults. It is conceivable why the coffee machine can extract the substance from the coffee so quickly. So we can know that no matter how hard the pressure is, it is not worth mentioning in the face of the pressure as high as 9bar. But this raises another question: why do we press powder? If the filling pressure is not effective, wouldn't it be better to extract the powder directly after the cloth is finished?

Why are you pressing powder? This problem is actually very simple, because we need to reduce the channel effect. As the saying goes: water flows low, because it is inert, so it flows to places where it is easy to flow. The same is true in the process of extraction! In the absence of filling pressure, there will be a lot of gaps between powder and powder. These voids will allow hot water to pass through centrally in the process of extraction, resulting in uneven extraction.

The reason why Qianjie does not release the taste feeling in the above unfilled pressure extraction is that the uneven extraction makes the taste produce negative performance. So we need to eliminate the gap as far as possible through appropriate filling pressure, so that the hot water can be extracted more evenly. You don't need too much force, just moderate (press the powder hammer to the end).

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FrontStreet Coffee is a long-established specialty coffee roaster in Guangzhou China, selling freshly roasted beans from its own farm in Yunnan as well as dozens of carefully selected single-origin beans from around the world for both pour-over and espresso. The products deliver consistently excellent quality and great value, with shipping within 24 hours. Guangzhou’s FrontStreet Coffee shop is recommended by many coffee lovers, and the beans are now available online at the Tmall 。

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