What is the reason why the coffee powder from the coffee grinder smells bad?

What is the reason why the coffee powder from the coffee grinder smells bad?

The problems of grinding speed and heat energy range from raw beans to baking to grinding into powder and making coffee. The closer to the finished product, the more "fragile" the coffee is. As long as the raw beans are properly stored, there will be no problem with them for a few months. Roasted coffee beans had better be finished within 3 weeks. If it is extracted under low pressure, one week is the best life cycle. If it is made of coffee, it will lose 50% of its fragrance in less than two minutes. The grinding process of the grinder will produce a lot of heat. Ground coffee is easy to oxidize and volatilize when exposed to air. (that's why coffee beans are ground.)

Therefore, the heat generated by the speed of the grinder has a considerable impact on coffee. In other words, the slower the speed of coffee, the less heat will be generated and the rate of oxidation of coffee will eventually decrease, but there is a paradox: "if the speed is slow, then the speed of flour will be slower." If the coffee shop is busy, don't you have to use a high-speed grinder? " Yes, but another way to achieve high output and low speed is to use a large diameter blade. Due to torque, grinding can be completed quickly even if the rotational speed is very low. For example, mazzer's current flagship product robur,73mm knife head can basically produce 20g powder in about 4 seconds, while the rotational speed as low as 450RPM (it takes about 20-30 seconds for Mazzer supper jolly 1500RPM to complete 20g powder production) has mentioned that the speed of the grinder has two effects on coffee, one is the speed of the powder itself, and the heat generated.

When grinding beans, the size of the powder depends on the way it is cooked. The shorter the cooking time, the finer the ground powder; the longer the cooking time, the thicker the ground powder. Sixth, in terms of the actual way of cooking, it takes a very short time for the ESPRESSO machine to make coffee, so the grinding is the finest, and the coffee powder is as fine as flour; it takes more than a minute to cook coffee in the "plug wind" way, and the coffee powder belongs to medium-sized grinding; American filter coffee takes a long time to make, so the coffee powder is the thickest, one by one like Beijing grains on a shell beach. Grinding coffee powder with appropriate thickness is very important for making a good cup of coffee, because the extraction of water-soluble substances in coffee powder has its ideal time, if the powder is very fine and cooked for a long time, resulting in over-extraction, the coffee may be very bitter and lose its aroma. On the other hand, if the powder is coarse and cooked too fast, resulting in insufficient extraction, the coffee will be tasteless because there is no time to dissolve the water-soluble substance in the powder.