What does channel effect mean in coffee? Why are there holes in the coffee powder cake?

Many coffee machine users now use bottomless handles. The so-called bottomless handle means that the bottom of the handle for fixing the powder bowl is open without a diverter nozzle. Using such a handle to extract espresso, we can observe the outflow of espresso from the beginning to the end of extraction, which can be said to be very healing throughout the process.

But occasionally, you should encounter this kind of outflow when using a bottomless handle to extract espresso: the espresso liquor does not penetrate completely vertically downward as usual, and some coffee liquor is "sprayed out" directly from the powder bowl and then splashed everywhere nearby. If this happens occasionally, then we don't need to pay too much attention. But if it appears very frequently, Qianjie will suggest that everyone re-examine their own series of processes before extraction and concentration, because this is likely to be the result of improper operation.

Although this situation does not necessarily make coffee difficult to drink, it will make it easier to extract a cup of coffee that is difficult to drink. There is a professional term for this situation in the circle called channel effect. So today, Qianjie will come to share with you why channel effects occur during extraction and concentration, and then how we should reduce the occurrence of channel effects.

Why is there a channel effect? That's right, we can only reduce the probability of its occurrence, and we cannot completely avoid it. Although Qianjie has shared it many times, in order to prevent some new friends from not understanding what the channel effect is, Qianjie will explain it briefly here. Channel effect is a common negative phenomenon in coffee, which means that water flows preferentially from places with low resistance due to inertia. In the extraction process of espresso, this phenomenon can easily lead us to extract a cup of difficult coffee.

Because the overall resistance of the powder cake is high, and then the coffee extraction time is relatively short, when there is a place where the resistance is small, a large amount of hot water will pass through this place in a short time, resulting in excessive local extraction and insufficient extraction in other places. This phenomenon of uneven extraction. If there is no surprise, the coffee extracted in this way will have a strong sour taste that is under-extracted and then a clear bitter taste. Then the powder cake after extraction will have many small holes, which are the channels created during the extraction process.

As Qian Jie said earlier, most of the reasons for the channel effect are due to improper operation. So if we want to avoid the emergence of channel effects as much as possible, then we can take a look at the following situations that you need to improve ~

1. Uneven powder distribution and powder pressing are two parts of filling coffee powder before extraction and concentration. The correct operation of these two steps is directly related to the probability of channel effects occurring. Front Street starts with cloth powder. The purpose of distributing powder is very simple, that is, to evenly distribute coffee powder in every corner of the powder bowl. Because only by evenly distributing the coffee powder can the resistance in every place of the powder cake be similar, so that hot water will not be concentrated in one place for extraction.

Although the purpose is simple, the reason why many friends frequently trigger channel effects is that they have not made a good job in distributing powder. It may be that it is to pursue speed, or it may be that cloth powder is not very important, so during the operation, you just randomly stir the coffee powder and go through the process. Some friends don't even know how to apply cloth powder and simply fill it. Extraction starts directly after pressing. So situations like these can easily cause channel effects to appear during the extraction process, making the coffee less delicious.

Therefore, if everyone does this when distributing powder, then the Front Street Association recommends that everyone pay attention to the operation of distributing powder. This will make it easier and more stable to extract a good cup of espresso ~

Second, uneven application of pressing powder is followed by pressing powder! After we evenly distribute the powder, the next thing to do is evenly press the powder. If the force we apply to every place when pressing the powder is not uniform enough, then the resistance of the part of the powder cake that is under more force will be higher, and the resistance of the part that is under less force will be lower. Naturally, hot water will preferentially flow to the part with low resistance during the extraction process for concentrated extraction, which will lead to uneven extraction.

From the above, you can know that whether it is cloth powder or pressed powder, correct operation is very important for the extraction of coffee. If you don't know how to make cloth powder and pressing powder well, you can search Qianjie's previous tweets, which will share specific practices in detail ~

3. There are bumps, but even if the cloth powder and pressed powder are prepared, we cannot take it lightly before the extraction begins. Because Qianjie observed that some friends were very casual when snapping the handle. They did not specifically aim or quickly find the accurate position based on habit, but only buckled the handle into the brewing head after bumps.

A situation like this can easily lead to a channel effect, because cracks will occur when the powder cake is bumped, and then hot water will concentrate and pass through these cracks. Therefore, when buckling the handle, we can try to reduce the number of bumps and complete them in one go, so that the occurrence of channel effects can be reduced.

4. The amount of powder is too small and the grinding is too rough. There are also problems with the amount of powder and grinding. When the coffee powder is ground too thick or the amount of powder is too small, it can easily lead to channel effects.

Because these two situations will make the resistance of the powder cake less high, it is easy for hot water to find a breakthrough and then concentrate on passing through this breakthrough, thereby creating a channel effect. Therefore, fine grinding and increasing the amount of powder are the best ways to deal with this situation. In addition, we can also reduce the generation of channels in this case by pressure swing extraction, that is, reducing the pressure during extraction. However, compared with the former, the stability of pressure swing extraction will be slightly lower and the difficulty will be slightly higher. Therefore, the Qianjie Association recommends that everyone use the former to make adjustments.

5. Too much agglomerated powder mentioned in front of Qianjie that operating problems are most but not all of the reasons for the appearance of channels. In addition to operational problems, there may also be problems with the coffee powder itself. Coffee beans tend to generate static electricity when they are ground. The finer the grinding degree and the drier the weather, the more electricity will be generated. The existence of static electricity will give coffee powder adsorption. They will adsorb various objects, or they will attract each other and gather together.

When the amount of lumps in coffee powder is too high, the probability of channel effects occurring is greater. Because the existence of these agglomerated coffee powder in the powder cake will also make differences in resistance in different places, and then allow hot water to slip away from places with low resistance first. A situation like this is also easy to solve. If you find that the ground coffee powder contains a lot of agglomerated coffee powder, you can first break it up with a cloth powder injection before applying the powder, and then press it with the cloth powder.

Well, if you don't have a powder for powder, you can also shake up the agglomerated coffee powder by knocking it. However, relatively speaking, its efficiency will not be as high. The above is the reason why espresso will splash during the extraction process and the solution. You can refer to it. If you make the same mistake, you can make timely improvements, so that it can be easier to make a delicious cup of coffee.

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