What is the reason why the hand-brewed coffee is blocked? Why can't I pat the filter cup? How does fine powder make coffee over-ripe?

I believe that there must be friends who, like Qianjie, will bring temporary "obsessive-compulsive disorder" when making coffee! If you see any irregularities in the process, you will always want to "repair" them into a flat appearance. For example, the preparation before brewing coffee, wet filter paper! When the filter paper does not fully fit with the filter cup, you will want to press down the protruding part of the filter paper so that it can fully fit with the filter cup!

Or the waiting time after the second stage of hot water injection, found that the gradually exposed powder bed is not uniform, so it will deliberately pour more water into the powdery area, so as to make the final powder pit more symmetrical. In addition, like when pouring powder, the distribution of powder in the filter cup appears more on the left and less on the right! Then we will want to flatten the powder by slapping the filter cup! It is thought that this will make the hot water extract all the coffee powder more evenly, and the coffee will be more delicious.

But in fact, this may be counterproductive because it is easy to trigger probabilistic events: the extraction process is prone to clogging and rushing out the negative smell of the extract.

Qianjie has done an experiment before, in which two portions of coffee powder are poured in at the same angle, then one is directly brewed, and the other is brewed after several slaps. The results were obvious that the untapped group completed the extraction in 2 minutes, while the slapped group completed the extraction in 2 minutes and 21 seconds, with a bitter taste because the water was blocked during the period.

Why does flattening a powder bed have such a consequence? Because, coffee machine grinding out of the particles are not absolutely uniform! Like extraction, all they can do is to make most of them the same, not all of them. So in a cup of coffee powder, there are both large and small grains. (large and small grains separated from the same coffee powder)

When we knock, the whole powder layer vibrates, which makes the large coffee powder run to the upper layer and the small fine powder to the lower layer. The Brazilian fruit effect that is often mentioned in the front street refers to this phenomenon. When the fine powder is accumulated in the lower layer, it is easier to block the filter paper, thus prolonging the extraction time and causing an accident in the extraction.

Not only that, if you knock too many times, when the fine powder runs to the lower layer, because their particle size is smaller, so the gap between powder and powder will be reduced! Under repeated knocks, the gap will shrink and make it more difficult for hot water to pass through! We can clearly see the consequences of this from steaming: a small amount of hot water will flow to the edge with inertia because it can not break through the powder layer quickly, and uneven extraction will be more likely to occur!

Therefore, the Qianjie Association recommends that you pay attention to the way of adding powder and pour it slowly to the center of the filter cup as far as possible, so as to reduce the uneven distribution of coffee powder, so that you do not have to bear the risk caused by tapping! But if, without paying attention, there is still a deviation in the distribution of powder, it doesn't matter. We only need to pick up the filter cup and shake it slightly to make it relatively flat! Do not use too many times, or the same situation will occur. (the following picture is exaggerated, do not imitate)

Slapping is not impossible, but the strength and frequency need to be mastered to avoid the Brazilian fruit effect! And the use of cloth powder needle will also be a good choice, which can not only flatten the powder bed, but also dredge the caked fine powder, hot water has more flow space, so the extraction is more uniform.

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