CN108175279B

CN108175279B - Coffee brewing method

Info

Publication number: CN108175279B
Application number: CN201711483633.2A
Authority: CN
Inventors: 王德涛
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-12-29
Filing date: 2017-12-29
Publication date: 2020-11-06
Anticipated expiration: 2037-12-29
Also published as: CN108175279A

Abstract

The invention provides a coffee brewing method, which comprises the following steps: wetting the coffee powder by hot water in the brewing device; extracting a portion of the coffee grounds with hot water in the brewing device at a first predetermined pressure; extracting the rest of the coffee powder with hot water in the brewing device at a second predetermined pressure, wherein the second predetermined pressure is less than the first predetermined pressure. The invention solves the problem that the extraction pressure can not be adjusted according to the requirements of different stages in the prior art.

Description

Coffee brewing method

Technical Field

The invention relates to the technical field of coffee brewing, in particular to a coffee brewing method.

Background

In daily life, coffee is popular with a wide range of consumers, and the following parameters mainly affect the taste of coffee in the process of brewing coffee: the coffee brewing method is easy to excessively extract in the final extraction stage, so that the taste of coffee is influenced, and the coffee brewing method capable of adjusting the extraction pressure according to requirements of different stages is needed.

Disclosure of Invention

The invention mainly aims to provide a coffee brewing method, which aims to solve the problem that the extraction pressure cannot be adjusted according to different stage requirements in the prior art.

In order to achieve the above object, the present invention provides a coffee brewing method, comprising the steps of:

wetting the coffee powder by using hot water in the brewing device;

extracting a portion of the coffee grounds with hot water in a brewing device at a first predetermined pressure;

the remaining portion of the coffee grounds are extracted with hot water in the brewing device at a second predetermined pressure, wherein the second predetermined pressure is less than the first predetermined pressure.

Further, the coffee brewing method uses a coffee machine for moistening and extracting coffee powder, the coffee machine comprising: the coffee powder extracting device comprises a main boiler, a sub boiler, a water supply device for supplying cold water and a brewing device, wherein the sub boiler is arranged in the main boiler, a water inlet of the main boiler and a water inlet of the sub boiler are respectively communicated with the water supply device, the main boiler is provided with a first heating device for heating water in the main boiler, the brewing device is respectively communicated with the water supply device and a water outlet of the sub boiler, the brewing device is provided with a water outlet hole, a water pump and a pressure reducing electromagnetic valve are arranged between the brewing device and the water supply device in parallel, the water pump is opened in the process of moistening and extracting one part of coffee powder, the pressure reducing electromagnetic valve is closed, the water pump is closed in the process of extracting the rest parts of the coffee powder, and the pressure reducing electromagnetic valve.

Further, the first predetermined pressure is in the range of 9-10 bar.

Furthermore, the time for extracting a part of the coffee powder is within the range of 14-18 s.

Further, in the process of extracting the rest part of the coffee powder, the first preset pressure is reduced to a second preset pressure, and the second preset pressure is 5-6 bar.

Further, the time for extracting the rest of the coffee powder is within the range of 0-6 s.

Further, the coffee powder is moistened at a third predetermined pressure, which is in the range of 2-4 bar.

Furthermore, the wetting time is within the range of 3-8 s.

Further, according to a coffee brewing method of any one of the above, the sum of the time of moistening, the time of extracting a part of the ground coffee and the time of extracting the rest of the ground coffee does not exceed 30 s.

Further, the temperature of the hot water in the brewing device remains constant during the wetting and extraction.

Further, the coffee machine also comprises a mixing device which uniformly mixes the hot water in the sub boiler with the cold water in the water supply device so as to keep the temperature of the hot water in the brewing device unchanged.

Furthermore, the brewing device comprises a brewing boiler and a brewing device which are arranged at intervals, the brewing boiler is communicated with the water outlet of the sub-boiler and the water supply device, the water containers of the brewing boiler and the brewing device are communicated through a first water flow channel and a second water flow channel which are arranged up and down, the brewing boiler, the second water flow channel, the water containers and the first water flow channel form a circulation loop, the brewing device is provided with a second heating device, the inner top wall of the brewing boiler is higher than the inner top wall of the water containers, the second heating device and the circulation loop form a mixing device, and the water outlet hole is formed in the bottom of the water containers.

The technical scheme of the invention has the following advantages: in actual use, water in the water supply device enters the main boiler 10, the main boiler 10 is heated by the first heating device 30, so that the sub-boiler 20 arranged in the main boiler 10 is heated, and hot water flowing out of the sub-boiler 20 and cold water flowing out of the water supply device are mixed in the brewing device. The brewing device can mix hot water and cold water to any temperature suitable for brewing coffee, so that the problem that the taste is poor due to overhigh water temperature for brewing coffee is solved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts. In the drawings:

figure 1 shows a schematic view of the internal structure of a coffee machine according to the invention;

FIG. 2 is a graph showing the pressure change during coffee brewing using a prior art coffee maker;

FIG. 3 is a graph showing the pressure change during coffee brewing using the coffee maker of the present application;

fig. 4 shows a schematic flow diagram of a coffee brewing method according to the invention.

Wherein the reference numerals in the above figures are:

10. a mother boiler; 11. steam boiling head; 12. a thermal head; 13. a pressure switch; 14. a water level probe; 15. a barometer; 16. an exhaust valve; 17. a safety valve; 20. a sub-boiler; 30. a first heating device; 41. a brewing boiler; 411. a water pressure gauge; 421. a water container; 4211. a water outlet; 422. a base; 4221. boiling the mixture; 4231. a first interface; 4232. a second interface; 4233. a third interface; 424. a water supply pipeline; 425. a brewing pipeline; 43. a first water flow passage; 44. a second water flow passage; 45. a second heating device; 51. a first tube section; 52. a second tube section; 521. a first check valve; 522. a flow regulating valve; 53. a third tube section; 54. a fourth tube section; 541. a water pump; 542. a water inlet electromagnetic valve; 55. a fifth pipe section; 552. a second check valve; 60. and (4) releasing the valve.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

An embodiment of a coffee maker as shown in fig. 1, comprises: the coffee machine comprises a main boiler 10, a sub boiler 20 and a water supply device for supplying cold water, wherein the sub boiler 20 is arranged in the main boiler 10, a water inlet of the main boiler 10 and a water inlet of the sub boiler 20 are respectively communicated with the water supply device, a first heating device 30 for heating water in the main boiler 10 is arranged on the main boiler 10, the coffee machine further comprises a brewing device with a water outlet 4211, and the brewing device is respectively communicated with the water supply device and the sub boiler 20 so as to enable hot water in the sub boiler 20 to be mixed with the cold water in the water supply device.

In actual use, water in the water supply device enters the main boiler 10, the main boiler 10 is heated by the first heating device 30, so that the sub-boiler 20 arranged in the main boiler 10 is heated, and hot water flowing out of the sub-boiler 20 and cold water flowing out of the water supply device are mixed in the brewing device. The brewing device can mix hot water and cold water to any temperature suitable for brewing coffee, so that the problem that the taste is poor due to overhigh water temperature for brewing coffee is solved.

Specifically, the coffee maker further includes a mixing device for uniformly mixing the hot water in the sub-boiler 20 and the cold water in the water supply device. The mixing device can uniformly mix cold water and hot water, and the brewed coffee has better taste.

Specifically, the coffee machine further comprises a PID temperature controller which is respectively electrically connected with the first heating device and the temperature sensor and controls the first heating device to work.

Specifically, the brewing device comprises a brewing boiler 41 and a brewing device which are arranged at intervals, the brewing boiler 41 is communicated with the sub-boiler 20 and the water supply device, the brewing boiler 41 is communicated with a water container 421 of the brewing device through a first water flow channel 43 and a second water flow channel 44 which are arranged up and down, the brewing boiler 41, the second water flow channel 44, the water container 421 and the first water flow channel 43 form a circulation loop, the brewing device is provided with a second heating device 45, the inner top wall of the brewing boiler 41 is higher than the inner top wall of the water container 421, the second heating device 45 and the circulation loop form a mixing device, and a water outlet 4211 is arranged at the bottom of the water container 421. The second heating means 45 is operated so that the temperature of the water around the second heating means 45 becomes high, because the density of the hot water is lower than that of the cold water, the hot water moves upward and flows to the brewing boiler 41 through the first water flow channel 43, at this time, the cold water at the lower part of the brewing boiler flows into the water container through the second water flow channel 44, and because the inner top wall of the brewing boiler 41 is higher than the inner top wall of the water container 421, according to the pressure formula of the liquid, the higher the height of the liquid is, the higher the pressure is on the bottom surface, and therefore, the pressure of the water in the brewing boiler 41 at the first water flow channel 43 and the second water flow channel 44 is higher than the pressure of the water in the water container 421 at the same density, so that the water in the boiler 41 also flows to the water container 421 through the first water flow channel 43 and the second water flow channel 44, but at this time, the hot water and the cold water are still not completely mixed uniformly, and the actual water temperature is, and the second heating device is controlled to work by utilizing the PID temperature controller, so that the actual temperature is consistent with the set temperature, and the actual water temperature can be accurately controlled by the mode.

Specifically, a water pressure gauge 411 is arranged on the brewing boiler, and the water pressure gauge can measure the water pressure in the brewing boiler and ensure that the water pressure in the brewing boiler is within a certain range through the cooperation of the water pressure gauge and the pressure release valve 60.

Specifically, the brewing device comprises a base 422 and a water container 421, the water container 421 is arranged on the base 422, a water outlet pipe is connected downwards at the water outlet 4211, a brewing opening 4221 is formed at one end of the water outlet pipe far away from the water outlet 4211, and a switch valve is arranged on the water outlet pipe. The water flowing out of the brewing port 4221 can brew coffee, and the on-off valve can control the opening or closing of the water outlet pipe.

Specifically, the switch valve is a two-position three-way valve, the two-position three-way valve divides the water outlet pipeline into a water supply pipeline 424 and a brewing pipeline 425 which are communicated with the water outlet 4211, a first connector 4231 of the two-position three-way valve is connected with the water supply pipeline 424, a second connector 4232 of the two-position three-way valve is communicated with the brewing pipeline 425, the two-position three-way valve has a first working position for communicating the first connector 4231 with the second connector 4232 and a second working position for communicating a third connector 4233 of the two-position three-way valve with the second connector 4232, the position of the brewing port 4221 is higher than that of the second connector 4232, and when the two-position three-way valve is located at the second working position, water in the brewing pipeline 425 is discharged through the second connector 4232 and. When the two-position three-way valve is in the first working position, the water in the water container 421 flows from the water supply pipeline 424 to the brewing pipeline 425 and finally flows out of the brewing opening 4221 for brewing coffee; when the two-position three-way valve is in the second working position, the water in the water container 421 flows from the brewing pipe 425 to the third port 4233 through the second port 4232, so that the waste water remained in the brewing pipe 425 is discharged, and the problem that the cold water remained in the brewing pipe 425 when the two-position three-way valve is in the first working position next time influences the temperature of the water for brewing coffee is avoided.

Specifically, a temperature sensor for detecting the temperature of the water at the water outlet 4211 or a position close to the water outlet 4211 is arranged on the brewing device. The temperature sensor is arranged near the water outlet 4211, so that the actual temperature of the water flowing out of the water outlet 4211 can be accurately measured.

Specifically, a water pump 541 is provided between the brewing device and the water supply device. The water pump 541 may increase the pressure of the water to conveniently supply water to the main boiler and to conveniently extract the coffee powder at a first predetermined pressure.

Specifically, the coffee maker further includes a pressure regulating solenoid valve disposed in parallel with the water pump 541. The pressure regulating solenoid valve can adjust the pressure of water.

Specifically, the pressure regulating solenoid valve is a pressure reducing solenoid valve. When the pressure reducing solenoid valve is opened and the water pump 541 is closed, the pressure reducing solenoid valve causes the pressure of the water to be reduced, which in turn causes the pressure of the water inside the brewing device to be reduced, and thus the pressure of the water eventually flowing out of the brewing orifice 4221 is reduced.

Specifically, a flow regulating valve 522 is provided between the water pump 541 and the brewing device. The flow control valve 522 facilitates regulating the flow of water, which may be varied by controlling the flow of water into the brewing device.

Specifically, the main boiler 10 is further provided with a steam boiling head 11 capable of foaming milk, a hot water head 12 for cleaning cups, a pressure switch 13 for controlling the operation of the first heating device 30, a water level probe 14 for measuring the water level, a gas pressure gauge 15 for measuring the gas pressure in the main boiler 10, a gas exhaust valve 16 capable of exhausting gas and a safety valve 17 for ensuring that the pressure in the main boiler 10 is within a safe range.

In particular, the coffee machine further comprises: the boiler comprises a first pipe section 51, a second pipe section 52 and a third pipe section 53, wherein one end of the first pipe section 51 is communicated with the sub boiler 20, one end of the second pipe section 52 is communicated with a water supply device, the other ends of the first pipe section 51 and the second pipe section 52 are both communicated with the third pipe section 53, the other end of the third pipe section 53 is communicated with a brewing device, and hot water flowing out of the sub boiler 20 and cold water flowing out of the water supply device flow through the third pipe section 53, so that the hot water and the cold water can be uniformly mixed in the brewing device conveniently.

Specifically, a water pump 541 and a water inlet solenoid valve 542 are arranged on the fourth pipe section 54 connected between the water supply device and the main boiler 10 along the water flow direction, the second pipe section 52 is connected on the fourth pipe section 54 between the water pump 541 and the water inlet solenoid valve 542, a first check valve 521 and a flow regulating valve 522 are arranged on the second pipe section 52 along the water flow direction, the first check valve 521 prevents the water from flowing backwards, and the flow regulating valve 522 controls the flow of the water.

Specifically, the third pipe section 53 is connected to a pressure relief pipe section, and a pressure relief valve 60 is provided on the pressure relief pipe section. Opening the pressure relief valve allows the water to drain, so that the pressure of the brewing boiler is reduced.

Specifically, the fifth pipe segment 55 is connected to the second pipe segment 52 located upstream of the first check valve 521, the fifth pipe segment 55 is communicated with the sub boiler 20, the second check valve 552 is arranged on the fifth pipe segment 55, the second check valve 552 prevents water from flowing backwards, and the cold water in the water supply device flows into the sub boiler 20 from the fifth pipe segment 55 through the fourth pipe segment 54 and the second pipe segment 52 in sequence.

The operation of the coffee maker in practical use will be described in detail with reference to fig. 1:

after the coffee machine is powered on, the water level probe 14 controls the water pump 541 to work, the water inlet electromagnetic valve 542 is opened, the water pump 541 starts to work, the water supply device supplies water to the main boiler 10 and the sub boiler 20, the water pump 541 and the water inlet electromagnetic valve 542 are closed after the main boiler 10 enters water to a normal water level, and when the water level probe 14 detects that the water level is lower than the normal water level, the water pump 541 and the water inlet electromagnetic valve 542 work, so that the water level in the main boiler 10 is kept within the range of the normal water level; the pressure switch 13 controls the first heating device 30 to work, the first heating device 30 heats water in the main boiler 10 to raise the temperature in the main boiler 10, when the temperature reaches a certain temperature, the exhaust valve 16 is opened and exhaust gas is discharged, the situation that the first heating device stops heating after the pressure reaches a certain value is avoided, then the heating pipe continues to work, the exhaust valve 16 is closed, the pressure in the boiler continuously rises, when the steam pressure in the main boiler reaches 1.1bar, namely the temperature is about 120 ℃, the pressure switch 13 controls the first heating device to stop heating, when the steam pressure in the main boiler is lower than 1.1bar, the first heating device continues to work, the temperature in the sub boiler 20 rises along with the temperature rise in the main boiler 10, water in the sub boiler 20 flows into the device to raise the temperature in the brewing boiler 41, and further the pressure in the brewing boiler 41 rises, when the pressure in the brewing boiler 41 exceeds 9bar, the pressure relief valve 60 is opened to discharge water and relieve pressure, so that the pressure in the brewing boiler 41 is always kept at 9 bar.

The coffee brewing process comprises the following steps:

setting different temperatures according to different coffee powders through a temperature control panel;

a wetting stage: the water pump 541 does not work, the two-position three-way valve is positioned at the first working position, water in the water container 421 flows out from the brewing opening 4221 to moisten coffee, the pressure is reduced from 9bar to 3bar, and the time of a moistening stage can be adjusted optionally according to requirements;

a high-pressure extraction stage: the water pump 541 and the flow control valve 522 are operated, the cold water in the water supply device and the hot water in the sub-boiler 20 are mixed in the brewing device, the second heating device 45 is operated, so that the temperature of the water around the second heating device 45 becomes high, because the density of the hot water is lower than that of the cold water, the hot water moves upward and flows to the brewing boiler 41 through the first water flow channel 43, at this time, the cold water in the lower part of the brewing boiler flows into the water container through the second water flow channel 44, and since the inner top wall of the brewing boiler 41 is higher than the inner top wall of the water container 421, according to the pressure formula of the liquid, the higher the height of the liquid is at the same density, the pressure to the bottom surface is larger, so that the pressure of the water in the brewing boiler 41 at the first water flow channel 43 and the second water flow channel 44 is higher than the pressure of the water in the water container 421, and therefore, the water in the brewing boiler 41 also flows to the water container 421 through the first water flow channel, but hot water and cold water still can not be mixed completely at this moment, and rethread temperature sensor detects actual temperature to utilize PID temperature controller to control second heating device work, make actual temperature unanimous with the settlement temperature, can accurate control actual temperature through above-mentioned mode. When the water pump 541 works, the pressure of water can reach 9bar, the flow regulating valve 522 can slightly increase the water pressure, and finally the water flows out of the brewing opening 4221 at the pressure of 9-10 bar to extract coffee powder, wherein the time of a high-pressure extraction stage can be randomly regulated;

a low-pressure extraction stage: the pressure reduction electromagnetic valve starts to work, the brewing pressure is reduced to 5-7 bar from 9-10 bar, the final low-pressure extraction is completed, then the two-position three-way valve is located at the second working position, water in the water container flows to the third connector from the brewing pipeline through the second connector, so that waste water remained in the brewing pipeline is discharged, and the problem that cold water remained in the brewing pipeline when the two-position three-way valve is located at the first working position next time influences the water temperature of water for brewing coffee is avoided. Set for the pressure in different low pressure extraction stages through controlling the step-down solenoid valve, can set for the pressure in different low pressure extraction stages according to the self characteristic of coffee powder to can extract the pressure too high when can avoid extracting at the end by the low pressure, and then lead to the coffee taste of extracting out bitter and astringent, wherein, the time in low pressure extraction stage can be adjusted wantonly.

As shown in FIG. 4, the method of brewing coffee by using such a coffee maker will be described in detail below:

the method specifically comprises the following steps:

wetting the coffee powder by using hot water in the brewing device;

the remaining portion of the coffee grounds are extracted with hot water in the brewing device at a second predetermined pressure, wherein the second predetermined pressure is less than the first predetermined pressure. The first preset pressure is set to fully extract the grease in the coffee powder, and the last-stage extraction is carried out under the second preset pressure, so that the phenomenon that the taste of the coffee is bitter due to excessive extraction is avoided.

Specifically, the first predetermined pressure is in the range of 9-10 bar. The water pressure in the brewing boiler is kept at 9bar all the time, the water pressure is slightly fluctuated by the control of the flow regulating valve, and finally, the coffee powder is extracted by high pressure in the range of 9-10 bar, so that the grease in the coffee powder is fully extracted.

Specifically, the time for extracting a part of the coffee powder is within the range of 14-18 s. The grease in the coffee powder can be fully extracted by high-pressure extraction, so that the coffee has mellow taste.

Specifically, in the process of extracting the rest part of the coffee powder, the water pressure in the brewing device is reduced from a first preset pressure to a second preset pressure and then is kept at the second preset pressure, and the second preset pressure is 5-6 bar. The end section adopts low-pressure extraction, so that the bitter taste of the coffee caused by excessive extraction is avoided.

Specifically, the time for extracting the rest of the coffee powder is within the range of 0-6 s. The time of the low-pressure extraction stage is shorter than that of the high-pressure extraction stage, so that the bitter taste of the coffee caused by excessive extraction is avoided.

Specifically, in the process of wetting the coffee powder, the water pressure in the brewing device is reduced from a first preset pressure to a third preset pressure and then is maintained at the third preset pressure, the third preset pressure is in the range of 2-4 bar, and in the process of extracting a part of the coffee powder, the water pressure in the brewing device is increased from the third preset pressure to the third preset pressure and then is maintained at the first preset pressure. The wetting process is similar to the stuffy steaming process when coffee is brewed by hands, grease in the coffee powder can be in mild contact with water in the stuffy steaming process, the grease is easier to separate from the coffee powder, meanwhile, carbon dioxide in the coffee powder can be discharged in a proper amount, and the grease is finer and smoother.

Specifically, the wetting time is within the range of 3-8 s. The moistening process makes the coffee more mellow in mouthfeel.

In particular, the sum of the time of moistening, the time of extraction of a portion of the coffee powder and the time of extraction of the remaining portion of the coffee powder does not exceed 30 s. The brewing time can be determined according to different coffee powders.

In particular, the temperature of the hot water in the brewing device remains constant during the wetting and extraction. The water temperature in the brewing device can be kept constant through the mutual matching of the second heating device and the temperature sensor.

The specific steps for brewing espresso are described below:

setting the water temperature to be 93 ℃;

a wetting stage: the wetting time is 5s, the water pressure in the brewing boiler is rapidly reduced from 9bar to 3bar and is stabilized to about 3 bar; the water pressure in the brewing boiler is naturally reduced due to the hot water flow.

A high-pressure extraction stage: setting the first preset pressure to be 9bar, rapidly increasing the water pressure in the brewing boiler from 3bar to 9bar, stabilizing the water pressure to be about 9bar, and setting the time of high-pressure extraction to be 15 s; the pressure in the brewing boiler rises continuously as the water in the brewing boiler is gradually heated and eventually stabilizes at 9 bar.

A low-pressure extraction stage: the second predetermined pressure was set at 6bar, the time for the low-pressure extraction was set at 6s, and the pressure was reduced from 9bar to 6bar in a time range of 6 s. The pressure reducing solenoid valve starts to work to reduce the brewing pressure and finish the final low-pressure extraction.

The process of brewing espresso coffee in a coffee machine of the prior art and the process of brewing espresso coffee in a coffee machine of the present application are described below:

fig. 2 is a pressure change situation of a conventional coffee machine in the prior art when espresso is brewed, the pressure of the conventional coffee machine is always constant, no wetting process is performed in the initial stage of brewing coffee, coffee powder is directly extracted through high pressure, a large amount of carbon dioxide is easily discharged, the drinking taste of coffee is further influenced, 9bar pressure is still kept in the final stage of extraction, and the coffee powder is easily subjected to transitional extraction, so that the bitterness is generated.

Fig. 3 is the pressure change condition when the coffee machine of this application is used to brew Italian coffee, the pressure of each stage is constantly changed when the coffee machine is used to brew coffee, the pressure of the wetting stage is gradually decreased from 9bar to 3bar, similar to the process of braising the coffee powder when the coffee is brewed by hand, the grease in the coffee powder can be gently contacted with water in the braising process, so that the coffee powder is more easily separated from the grease, meanwhile, the carbon dioxide in the coffee powder can be properly discharged, and the grease is more delicate. The pressure of the high-pressure extraction stage is about 9bar, and the grease in the coffee powder can be fully extracted at the pressure of 9 bar. When coffee is extracted to the tail section, soluble substances in coffee powder are less and less, the coffee machine in the application can adopt low-pressure extraction at the stage, the pressure can be reduced to 6bar from 9bar, the coffee taste is ensured to be complete, excessive extraction is prevented, and the Italian coffee with perfect taste is made.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.

Claims

1. A method of brewing coffee, comprising the steps of:

wetting the coffee powder by using hot water in the brewing device;

extracting a portion of the coffee grounds with hot water in the brewing device at a first predetermined pressure;

extracting the rest of the coffee powder with hot water in the brewing device at a second predetermined pressure, wherein the second predetermined pressure is less than the first predetermined pressure;

the coffee brewing method uses a coffee machine to wet and extract the coffee powder, the coffee machine comprising: the water supply device comprises a main boiler, a sub boiler, a water supply device for supplying cold water and the brewing device, wherein the sub boiler is arranged in the main boiler, a water inlet of the main boiler and a water inlet of the sub boiler are respectively communicated with the water supply device, the main boiler is provided with a first heating device for heating water in the main boiler, the brewing device is respectively communicated with the water supply device and a water outlet of the sub boiler, and the brewing device is provided with a water outlet hole;

the coffee machine also comprises a mixing device for uniformly mixing hot water in the sub boiler and cold water in the water supply device, wherein the brewing device comprises a brewing boiler and a brewing device which are arranged at intervals, the brewing boiler is communicated with the water outlet of the sub boiler and the water supply device, the brewing boiler is communicated with a water container of the brewing device through a first water flow channel and a second water flow channel which are arranged up and down, the brewing boiler, the second water flow channel, the water container and the first water flow channel form a circulation loop, the brewing device is provided with a second heating device, and the inner top wall of the brewing boiler is higher than the inner top wall of the water container, the second heating device and the circulation loop form the mixing device.

2. The coffee brewing method according to claim 1, wherein a water pump and a pressure reducing solenoid valve are connected in parallel between the brewing device and the water supply device, the water pump is turned on and the pressure reducing solenoid valve is turned off during extraction of a part of the coffee grounds, and the water pump is turned off and the pressure reducing solenoid valve is turned on during extraction of the rest of the coffee grounds.

3. A coffee brewing method according to claim 1, characterized in that said first predetermined pressure is in the range of 9-10 bar and/or the time for extracting a portion of said coffee powder is in the range of 14-18 s.

4. A coffee brewing method as claimed in claim 1, characterized in that during the extraction of the rest of the coffee powder, the water pressure in the brewing device is reduced from the first predetermined pressure to the second predetermined pressure and maintained at the second predetermined pressure, the second predetermined pressure being 5-6 bar, and/or the time for the extraction of the rest of the coffee powder is in the range of 0-6 s.

5. A coffee brewing method as claimed in claim 1, characterized in that during the moistening of the coffee powder, the water pressure in the brewing device is reduced from the first predetermined pressure to a third predetermined pressure and is maintained at the third predetermined pressure, the third predetermined pressure being in the range of 2-4 bar; during the process of extracting a part of the coffee powder, the water pressure in the brewing device is increased from the third preset pressure to the first preset pressure and then is kept at the first preset pressure; and/or the wetting time is within the range of 3-8 s.

6. A coffee brewing method as claimed in any one of the claims 1 to 5, characterized in that the sum of the time of moistening, the time of extracting a part of the coffee powder and the time of extracting the remaining part of the coffee powder does not exceed 30 s.

7. A method of brewing coffee as claimed in claim 2, wherein the temperature of the hot water in the brewing device is kept constant during the wetting and extraction.

8. A method as claimed in claim 1, wherein the outlet is provided at the bottom of the water container.