There are four main factors affecting extraction by bean grinder.

Uniformity: Coarse coffee particles are more easily extracted, while finer particles will be extracted in advance, so the larger the coffee powder, the more turbid and irritating the taste. However, when coffee powder with the same grinding particle size and relatively similar shape is extracted, the taste becomes brighter and stronger, and the performance of flavor characteristics is clearer and more consistent.

Fine powder: Coffee powder close to flour will be easily extracted and even dissolved in water, thus affecting the extraction taste of coffee. The more fines, the easier it is to over-extract coffee and the more bitter it tastes. When making espresso coffee, the fine powder will be washed out into the cup by the water flow. If extracted properly, the dense oil will lift the fine powder, and the fine powder will float on the surface of the oil to form a beautiful "tiger spot". But "tiger spot" doesn't represent how espresso tastes. The production of fine powder can be reduced by selecting a better bean grinder or using a screen. However, if there is no fine powder at all, the brewed coffee will also lack a sense of hierarchy, and the balance can only be practiced, not explained.

3, calorific value: any grinder grinding wheel in the grinding process will generate heat, coffee powder heating will accelerate the oxidation process, accelerate the aroma volatilization, resulting in brewed coffee flavor weakened. The calorific value of the cutter head depends on many factors such as the size of the grinding disc, the material, the structure of the cutter, the fineness of the grinding, the speed of the motor, the hardness of the coffee beans and so on. Therefore, at present, large brands of bean grinders are beginning to be equipped with heat dissipation windows, refrigeration fans, metal that is easier to dissipate heat, or motor motors with higher torque and lower speed to drive the cutter head, thus reducing heat generation.

4, static electricity: In general, the finer the grinding, the faster the grinding machine, the stronger the static electricity generated; the internal material is plastic, the lower powder mouth does not use the static electricity reduction design of the grinding machine, the static electricity generated is stronger; The coffee beans with rich fat and deep roasting degree are ground, and the static electricity generated is stronger. Italian bean mill in the grinding often appear fine powder into a group, affecting the density of the powder after the cloth, resulting in uneven extraction; and single bean mill powder outlet magnet is through electrostatic adsorption silver skin and fine powder, to help reduce excessive extraction taste and miscellaneous taste.