What happened when the flushed pink wall broke in two?

Last week, we discussed the topic of why hand-brewed coffee is filled with water in a circle, and learned that it is to improve the extraction rate, at the same time to prevent the flow of water everywhere, to help it set the flow route, so as to achieve the goal of uniform extraction. When the flushed powder pit is in a "bowl shape", the powder wall at the edge of the filter cup and the bottom form a flat gentle slope, which indicates that the whole ring water injection process has been ideally controlled.

In the past two days, some novice friends felt that the coffee they made was not very good, and the powder pit did not seem to be consistent with the one in the tutorial, so they asked what the reason would be in front of the street. The "pit" provided by this friend looks like this: the powder wall on the filter cup is obviously broken in two, the middle circle of powder wall is very thin with a little bubble, there are few particles, and part of the coffee grounds is washed to the bottom, probably just like the picture below.

This kind of powder pit problem should be caused by the method of water injection, and the main reason why the powder wall is broken in two is that the water injected at the end is too strong. We might as well imagine that when the steaming is over, the second stage of target water is injected into the filter cup according to the cooking plan, and the stirring of the water column makes the coffee powder dissociate where the liquid surface touches, and as the liquid level gradually drops, the surface particles stick to the filter paper to form a powder wall of uniform thickness.

When the liquid level falls to 2GP3 of the height of the filter cup, if you are anxious to inject the last section in a large circle with a large current at the same time, the water column with excessive strength will break through the original stacked wall, and at the same time, this section of coffee powder will be washed down, thus forming a form of breaking into two parts. If you continue to inject water into the broken part, the hot water will flow directly through the filter paper from the ribs at the edge of the cup, resulting in a "channel effect", that is, uneven extraction. This explains why the coffee made by that friend doesn't taste right.

In addition to faults, in fact, there are also some cases because the circle is too large, this kind of powder pit looks like this.

Such pits usually occur because the water injection surface of the back section completely overflows the original powder wall, although it does not reach the filter paper, but because the overflowing water will slip away directly from the edge of the ribs, resulting in insufficient extraction or reduced concentration. The fine powder washed to the bottom may block the filter paper, causing stagnant water. The judgment is based on the fact that the powder wall at the top of the powder pit is covered with scattered coffee particles, the extraction time is usually more than 2 minutes and 10 seconds, and the coffee has an unpleasant bitter taste.

The above two situations are believed to have been encountered by many brewers during the novice period. If you want to improve the taste of coffee and at the same time improve your extraction skills, Qianjie suggests using a steady approach to practice the basic skills of flow control. The higher the water flow, the stronger the penetration, the more obvious the strength of scouring the coffee powder layer; on the contrary, the lower the water column, the softer the strength, the smaller the tumbling degree of the coffee powder layer. After understanding this truth, we can adjust the flow and the size of the circle according to different stages of water injection.

Take the three-stage style commonly used in the front street, for example, at the end of steaming, it will first take a steady vertical flow, maintain a uniform distance from the liquid level 3-4cm to wash the powder layer around, and constantly expand the range clockwise from the center to the periphery until the weight of the timing scale shows 125g.

As the liquid level rises, there will be less and less coffee powder that can be attached to the filter paper. when the water level falls to half, it can be injected gently with a small flow of high 2cm around a concentric circle along the radius of the liquid level. In this way, the particles in the filter cup can be "stained with rain and dew", the flavor substances can be fully released, and the original powder wall can be effectively avoided, resulting in uneven extraction.

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Front Street Cafe

No. 10 Baoqian street, Yandun road, Dongshankou, Yuexiu district, Guangzhou, Guangdong province