What is the reason for the sinking in the middle of hand-made coffee after steaming | A brief analysis of the sunken pit formed by hand-made coffee

In hand-brewed coffee, the steaming stage is our "first game" with coffee powder. If there is a complete and uniform "hamburger" in the coffee powder layer, this lays the foundation for "victory". If the coffee powder layer does not expand at all, there is a good chance that the coffee beans are not fresh and the coffee will not taste good.

But there is a situation, when steaming and injecting water, the coffee powder layer expands, but soon, there is a collapse in the middle, concave in, is this normal?

It has expanded, but it has not completely expanded. First of all, Qianjie first analyzes why this phenomenon occurs. If the coffee powder layer expands, it shows that the coffee powder is emitting gas, which eliminates the situation that the coffee beans are not fresh. The collapse after expansion is mainly due to the fact that the gap between coffee particles becomes larger when the coffee powder layer emits gas, and after the gas is discharged, these structures become loose, and if the pressure at the top of the center is too high, then it is impossible to maintain such a fluffy structure, so it has to collapse in the middle. What is the cause of this situation? -when the amount of water injected is too much, the amount of water injected by steaming is about 2 times that of powder, but sometimes we will inadvertently inject too much water. For example, when we use a simulation of shallow roasted coffee beans in the current street, when 15g powder is steamed around a small circle and injected with water 30ml, the coffee powder layer is still bulging after 30 seconds. When the 15g powder center was injected with water in a small circle of 40ml, it was found that the water level of the powder layer increased, and at 23 seconds, as the steaming liquid flowed down, the center of the powder layer "Hamburg" collapsed slightly.

-Water injection is too violent. Generally, steaming water is injected in a circle from the center to the outside, and the coffee "hamburger" slowly expands around from the center, in some fluffy coffee powder (such as medium and deep roasting). Even a small circle in the center can make the coffee "hamburger" expand from the center to all around.

Therefore, in terms of the results, there is not much difference between a small circle or a big circle, and we can consider using it according to the actual situation. But the gentle and violent way of water injection has a distinctive effect on the state of the powder layer. Gentle water injection will not have much impact on the structure of the powder layer; while for the more intense water injection, if you only focus on the small circle of water injection in the center, then the distance between the powder particles directly impacted by the water column will be larger, and the main reason why the center can stand up is that the gas discharge hinders the decline of water, and when the gas is discharged, the water flows down, and the rest is the empty powder layer, which naturally collapses. If the coffee powder is too coarse, water will flow into the next pot before it can infiltrate into the coffee particles. When coffee powder comes into contact with water at the beginning, gas is discharged from the surface to enlarge the gap between the coffee particles, that is, to expand, while water flows into the lower pot without entering the inside of the coffee particles, making these gaps unsupported and prone to collapse.

Sinking during steaming is obviously not a normal phenomenon, it reflects that there is something wrong with our parameters or techniques. Therefore, when we have the phenomenon of steaming and sinking during cooking, we need to "prescribe the right medicine to the case", find out the problem from the parameters and techniques and solve it.