What do you need to pay attention to when making cold coffee? Why is it that the finer the grinding, the lighter the cold-extracted coffee?

Recently, Qianjie received such a private message backstage that a friend wanted to drink cold coffee with a stronger flavor, so he adjusted the grinding to a very fine state. As a result, the taste of cold coffee is much lighter than the original! This puzzled him. It was obvious that the grinding had been fine-tuned, but why was it lighter?

Normally, we want to adjust the extraction efficiency of cold-extracted coffee, starting from grinding is really a good way! However, we cannot apply the conventional grinding theory to cold-extracted coffee. The conventional grinding theory is: if you want to reduce the extraction efficiency, then the grinding needs to be coarsely adjusted; if you want to increase the extraction efficiency, then the grinding needs to be adjusted finely! This is mainly by controlling the total surface area of the powder to adjust the extraction rate. The finer the grinding, the larger the total surface area and the larger the surface area, the easier it is to be infiltrated by hot water and extract rich coffee substances!

However, why is this theory not practical when it comes to cold extraction? The answer is actually very simple. Let's take a look at an experiment done under the front street.

In front of the extraction experiment, two kinds of coffee powder of different thickness will be used to make cold extracted coffee to see what is the difference between them! The coffee beans used in this experiment are Baja, Costa Rica, and the grinding used in hand flushing is the 9.5 scale of Ek43. When applied to cold-extracted coffee, it needs to be 0.5 fine, so it is the 9 scale of Ek43! Then we prepare another coffee powder which is finer than it and compare it with the extraction. The extraction parameters are as follows: amount of powder: 20g grinding scale: 9 scale of Ek43, 8 scale of y&Ek43

Ratio of powder to water: 1:10 (200ml) refrigerated time: 8h

After the cold storage is over, we filter it out and test the concentration separately! The results are as follows: the Baja cold extraction concentration of conventional grinding is 2.3%, while that of finer grinding is 2.1%. It can be seen that the coffee concentration after fine adjustment is indeed a little lower. The reason for the low concentration is actually very simple, that is, the coffee is in a long-standing state in the process of cold extraction. At first, most of the coffee powder will float on the liquid surface after being impacted by the water. As the soaking time lengthens, these floating particles gradually absorb enough water, so at this time, they begin to sink as they gain weight.

The coffee powder that sinks to the bottom will evolve different extraction efficiency according to the size of the particles! Coarse ground coffee powder because its own particles are uneven and large, when stacked together, there are a lot of gaps to supply water through, so that water has a rich extraction space; while grinding fine particles will be because their own particles are smaller, can be perfectly bordered with other particles, form a ball, the water area is greatly reduced, resulting in low extraction efficiency. Therefore, it can be extracted more slowly than coarse powder! This is why coffee powder is ground more finely, but the concentration of coffee extracted is lighter than that of coarse powder.

Therefore, Qianjie suggested that grinding and fine adjustment is a good way to increase the concentration, but please do not adjust it too much. After all, we have no way to shake and stir it regularly, which is too cumbersome for the production of Lengjie. Then, when the grinding degree is out of control, reducing the ratio of powder to water and prolonging the time of cold storage and soaking can also increase the concentration of cold extracted coffee. If it is too strong, it can also be diluted by ice! After all, thick can be diluted, but light, can not be saved!

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Front Street Cafe

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