Why does espresso espresso machine use 9bar to extract coffee under pressure

Qianjie often talks about the extraction relationship among powder quantity, proportion, grinding degree and time when sharing the knowledge of espresso extraction. As long as you master these four parameters, you can operate the espresso machine flexibly. However, there is another parameter, which is usually mentioned at once, but it is the most critical parameter of espresso extraction, which is pressure.

We know that the extraction method of the espresso machine is different from that of brewing coffee in that the former is pressurized and the latter is atmospheric pressure. Pressure extraction makes it easier to make full-bodied coffee, and the golden Crema can only be made under pressure. In all kinds of espresso extraction teaching and coffee machine instructions, the extraction pressure of espresso is 9bar, as if "espresso extraction pressure = 9bar" is engraved in everyone's memory as a truth. So why does everyone take the pressure of 9bar as the standard?

In front of the street, let's first talk about a concept, pressure is divided into pump pressure and extraction pressure, what we call 9bar pressure refers to the pressure of extraction, you can observe the pressure gauge, if you open the button, the pressure gauge starts to move, which represents the pressure of the pump. If you do not buckle the handle, the pressure gauge does not respond, the powder filling button is fastened to the handle and then the pressure gauge starts to move. This means that the pressure gauge is the extraction pressure gauge. Because the pressure source of the espresso machine mainly depends on the booster pump in the body, the machines on the market are mainly divided into vibration pump and rotary pump. Vibrating pumps generate pressure through high-speed and repeated vibrations of a piston-like structure, so it is difficult to ensure that the pressure is maintained in a short period of 30 seconds. This type of pump is usually set at the pressure of 15bar, but it may be able to climb slowly to 15bar at first, and then quickly reduce the pressure, lower than 9bar. There are also some household machines whose water flow is small, so the extraction pressure is lower than the pump pressure. The rotary pump produces pressure through the high-speed rotation of the metal sheet, the pressure output response is fast, and the pressure is more stable. It is generally used in commercial machines and high-end household machines, and the pump pressure is basically the same as the extraction pressure. Since you want to know why 9bar is used as the standard, you can do a small experiment to see how espresso performs under different pressures. The coffee machine with rotary pump is used in the front street, and the pressure can ensure that the pressure is in a stable range during the extraction process. The parameters are based on 9bar. Under the standard 9bar pressure extraction, 40g espresso is extracted with 20g coffee powder and the extraction time is 29 seconds. Then the front street uses the same parameters, but the pressure is adjusted to 6bar extraction. According to the pressure gauge of the boiling head, it takes 7 seconds for 0bar-6bar to extract 0-9bar (usually 5-6 seconds for 9bar extraction), the overall flow rate is slower than 9bar, and the final extraction time for 40g espresso is 36 seconds.

From the point of view of the richness of oil, it is comparable to 9bar, but the oil is relatively rough and dissipates faster than 9bar. Compared with the taste, the espresso liquid extracted by 6bar is less rich in aroma and sour taste, softer and heavier.

The next step is to adjust the pressure to 11bar. According to the pressure gauge, it takes 5 seconds from 0 to 11bar. At first, the flow rate is similar to that of 9bar, but the later flow rate is slightly faster than that of 9bar, and the final time is 27 seconds.

There is not much difference in grease. By tasting, 11bar's espresso will be more exciting and full-bodied than 9bar.

Qianjie makes this comparison, just to make it clear that when the pressure is lower, the extraction time will be longer, and the performance of the oil will be inferior, and the taste will be "insipid". When the pressure is greater, the extraction time will be shorter, and the taste will be more intense and exciting. And 9bar was used as the extraction pressure standard of espresso because in Italy in the 1960s and 1970s, when the pump-pressurized coffee machine and its popularity replaced the ancient version of the 3-4bar coffee machine, the new coffee machine had higher pressure, and then there was a problem. It was not that the higher the pressure, the better the coffee. They found that the coffee was extracted with a pressure higher than 9-10bar. Prone to the smell of charred wood, this taste is not pleasant, so slowly, we will find that 9bar pressure extraction of coffee concentration, taste have a good performance, so they default to use 9bar pressure extraction espresso. With the popularity of the pressure swing function of the new coffee machine, more and more people use pressure swing extraction, that is, to choose the flavor substances of coffee by artificially changing the extraction pressure. The whole process of 9bar extraction is not the only standard for the extraction of coffee.