How much pressure should I use to press the espresso cloth powder? Does the pressing power affect the extraction time of espresso?

Many friends have this understanding of the pressing process of espresso coffee when they first started, that is, they think that the strength of pressing powder will have a great impact on the extraction of espresso coffee! For example, if the greater the force used to press the powder, the more firm the powder will be, and the longer the time it will take to extract espresso coffee, because hot water cannot easily pass through the powder; conversely, the lighter the powder is, the looser the powder will be, and hot water can easily pass through the powder, which will shorten the extraction time, which will affect the extraction rate and taste of the coffee.

This is the truth, but is it really the case? Qianjie once conducted such an experiment to verify the authenticity of things-using three different strengths to fill a portion of coffee, and then extract it to see if there were obvious differences in the time they were extracted and the taste of the coffee. The coffee beans used are the medium-to-deep baked Italian blend in Qianjie Bean List-Qianjie Classic Blend. The extraction parameters are 20g of powder and a powder-to-liquid ratio of 1:2. Then, the forces used to compress the coffee powder were 2 kg, 5kg, and 20kg respectively.

After the extraction is completed, the extraction times used by them are: 29s, 30s, and 30s respectively. It can be seen that there is almost no difference. Since the parameters have not changed much, the taste will naturally not be much different. The performance of the three is the same, and they all have a balanced taste. The flavors of chocolate, caramel, butter, and cream are mellow and have a long aftertaste, which is very good. Does this result mean that the strength of pressing the powder will not affect the extraction? Of course not. It has an impact, but the impact is not as great as everyone thinks. The reason is also simple, because the pressure we use to extract coffee is much greater than the force we use when pressing the powder.

Generally speaking, the average pressure used by coffee machines to extract espresso is around 9bar. If a pressure of about 9bar is converted into force, then for a powder cake with a diameter of 58mm, the force exerted on them is about 243kg, which is equivalent to the weight of four adults. It is precisely because this force is so extreme that hot water can penetrate through the extremely high density coffee powder cake in a short period of time to dissolve the flavor substances inside. At the same time, it is precisely because of this that the strength with which we fill the powder cake before extraction will not have much impact on the extraction of coffee. After all, it is almost negligible in comparison.

However, there is no effect at all. Pressing hard can indeed make the powder cake more solid, but the main object of the impact is not time, but the probability of the channel effect occurring. The extraction of espresso usually involves injecting water first, and then starting pressure and extraction. If you don't fill the powder cake well in the powder distribution process, there will be a lot of gaps inside the powder cake. This will have a relatively high impact on the extraction of coffee, because hot water will preferentially flow to these channels during the extraction process, promoting the formation of channel effects.

So when filling the coffee powder before extraction, we can use a little force to fill the coffee powder, so that there are not many channels for hot water to flow easily, reducing the probability of channel effects. Of course, instead of using too much force to press the powder, the Qianjie Association recommends that everyone focus on how to evenly press the powder and try not to press the powder bed with one side high and the other low. Because if the powder bed is uneven, then the inert hot water will preferentially flow to the low point where it is easy to flow during the extraction process, which will also cause uneven extraction.

Therefore, it is not only the intensity of powder suppression, but the method of powder suppression is also something worthy of everyone's attention. Qian Jie has shared it in previous tweets, so I won't go into it too much here ~

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