GB2598528A

GB2598528A - A method of preparing a re-boiled soy milk

Info

Publication number: GB2598528A
Application number: GB1715024.4A
Authority: GB
Inventors: Chen Baoguo; Meng Haipeng; Li Xiaojun; Wen Wenxian
Original assignee: Fujian Dali Food Technology Co Ltd
Current assignee: Fujian Dali Food Technology Co Ltd
Priority date: 2017-07-04
Filing date: 2017-09-19
Publication date: 2022-03-09
Also published as: GB201715024D0; CN107183198A

Abstract

A method of preparing a re-boiled soy milk comprises the steps of (a) initial preparation of soybeans to obtain soy liquid, (b) boiling of the soy liquid, (c) separating of the bean dregs from the boiled liquid, (d) re-boiling of the separated soy liquid, (e) centrifugal separating to remove residues and obtain a soy milk, (f), cooling of the soy milk, and (g) standardising the protein content. The initial preparation step (a) includes soaking the soybeans at constant temperature for a predetermined time in a sealed tank 1, and grinding the soaked beans in a grinder (6, fig. 2) to obtain the soy liquid. During soaking, oxygen is expelled using nitrogen 123. The boiling step (b) comprises heating the soy liquid under normal pressure to 70-80°C, then boiling under micro pressure for 5-10 minutes. The re-boiling step (d) comprises maintaining the separated soy liquid at 85-95°C, then re-boiling under micro pressure for 5-10 minutes. The micro pressure in steps (b) and (d) is 0.03MPa-0.08MPa. The prepared soy milk may be sterilised by UHT sterilisation and packaged. The soaking in step (a) may be for 6-8 hours at 20-28°C, and the grinder 6 may be a stone mill.

Description

A METHOD OF PREPARING A RE-BOILED SOY MILK

The present invention relates to a processing method of soy milk, and more specifically relates to a method of preparing a re-boiled soy milk.

Soy milk is rich in high quality protein and a plurality of micro nutrients that a human body needs. Its nutritional value is similar to milk. Unlike milk, soy milk does not contain lactose. Lactose requires the action of lactase so as to be absorbed by a human body. However, many adults in China do not have enough lactase and suffer from lactose intolerance. The lack of lactase is also the major reason for diarrhea after consuming milk.

Further, soy milk is also rich in several substances such as unsaturated fatty acid, soy isoflavones and lecithin that are beneficial to human body for lowering cholesterol level and preventing high blood pressure and other diseases like coronary diseases and diabetes. Also, soy milk can strengthen the immune system and slow down general aging. Thus, soy milk which is rich in nutrition is suitable for breakfast, and it is very adaptable to the bodies of Chinese people.

Soy bean contains anti-nutritional factors such as saponin. The bitter taste of saponin affects the taste of soy milk. Also, saponin can easily create bubbles which have poorer heat conductive property. Conventionally, industrialized production of soy milk involves boiling once only. However, boiling soy liquid having bubbles once only usually cannot completely destroy the enzymes, and so resulting in poorer taste of the soy milk. Boiling is a crucial step for preparing soy milk, and so the handling of substances like saponin will directly affect the taste of the soy milk.

Moreover, soy liquid is conventionally boiled under normal pressure. Usually, boiling under normal pressure requires longer heating time for destroying enzymes and killing micro bacteria. Yet, boiling under normal pressure usually cannot eliminate enzymes and micro bacteria completely, and thus affecting the quality of the resulting soy milk product. CN103749708A discloses a soy milk and a method of micro pressure boiling for preparation thereof, in which soy liquid before boiling has to be de-aerated first. Therefore, the preparation is more complicated. Also, boiling the soy liquid for once only may still result in the aforesaid problem of incomplete elimination of enzymes and micro bacteria, hence affecting the product quality and inflicting the risk of food safety.

Nowadays, the market provides a lot of soy milk products made from peeled soy beans. The taste of soy milk made from peeled soy beans is simple without variations, and it contains lesser nutrition and has an unsatisfactory taste. Soy bean skin contains soybean polysaccharides which can better dissolve into the soy milk after several steaming and boiling, thereby enriching the taste of the soy milk and increasing its nutritional value.

In view of the aforesaid disadvantages of the prior art, the present invention provides a method of preparing a re-boiled soy milk. The soy milk prepared by the method disclosed herein has a rich taste and is safe to consume.

The present invention has the following technical scheme: A method of preparing a re-boiled soy milk, comprising the following steps: (1) Initial preparation: Remove impurities in raw soy beans to obtain soy beans; soak the soy beans in a constant temperature soy bean soaking tank under constant temperature for a predetermined time duration; during soaking, feed materials via a material inlet into the constant temperature soy bean soaking tank which is connected and in communication with a constant temperature water storage tank via a pipeline system, wherein an amount of the materials being fed is determined by a ratio of soy beans to water for soaking; when a thermometer provided at a water outlet end of a constant temperature heating device connected to a pipe section between the constant temperature water storage tank and the constant temperature soy bean soaking tank shows a temperature which meets a predetermined temperature required for soaking the soy beans, pure water is filled into the constant temperature soy bean soaking tank; after feeding of materials into the constant temperature soy bean soaking tank, amounts of soy beans and water in the constant temperature soy bean soaking tank meet a predetermined beans to water ratio required; when soaking the soy beans, the constant temperature soy bean soaking tank is maintained in a sealed condition a nitrogen supply device connected and in communication with the constant temperature soy bean soaking tank via a pipeline system supplies nitrogen into the constant temperature soy bean soaking tank, thus the constant temperature soy bean soaking tank is filled with nitrogen, and oxygen inside is expelled; stir the soy beans with nitrogen once an hour; after a predetermined period of soaking under constant temperature, the soy beans can be released; the soaked soy beans are grinded to obtain a soy liquid; (2) Boiling: heating up the soy liquid under normal pressure to 70-80°C, and then boiling the heated up soy liquid under micro pressure which is 0.03MPa-0.08MPa for 510 minutes to obtain a boiled soy liquid; (3) Separating: pressing the boiled soy liquid to separate bean dregs therefrom; wherein a filter net used for separating the bean dregs has a mesh hole diameter of 0.35-0.6mm; (4) Re-boiling: keeping the boiled soy liquid with the bean dregs separated at 8595°C, and then re-boiling the soy liquid under micro pressure which is 0.03MPa0.08MPa for 5-10 minutes to obtain a re-boiled soy liquid; (5) Centrifugal separating: subjecting the re-boiled soy liquid to high speed centrifugation at a speed of 3600-4500r/min to eliminate residues, thereby obtaining a soy milk; (6) Cooling: cooling down the soy milk to 4-15°C; (7) Standardizing index: detecting a protein index of the cooled down soy milk and then adjusting its protein contents to 2.5-4.5%; (8) Sterilizing sterilizing the soy milk after index standardization by UHT sterilization under 137-142°C for 5-35 seconds; (9) Sterile packaging: filling the soy milk sterilized by UHT sterilization into packaging bottles.

When soaking the soy beans in step (1), the soy beans are soaked in the constant temperature soy bean soaking tank at a temperature of 20-28°C for 6-8 hours. Grinding of the soy beans in step (1) is performed by stone milling.

The soy beans in step (1) are organic soy beans, and impurities in the soy beans are removed in step (1) by one or more than one of the following methods: winnowing, magnetic separation and specific gravity sorting.

After step (7), bag-type filtering of the soy milk using a filter net having 100-300 meshes is performed; sterilizing and sterile packaging are performed after filtering.

The method of preparing a re-boiled soy milk of the present invention has the following beneficial effects: (1) Safer and more hygienic, and has a longer preservation period. Soy beans contain saponin which forms bubbles. Bubbles have poor heat conductivity. Therefore, after soy liquid is boiled for the first time, substances especially like enzymes and micro bacteria on the bubbles may not be completely killed and destroyed due to insufficient heat caused by poor heat conductivity. Accordingly, there is a risk of unhygienic and unsafe food. Also, saponin has a bitter tone that affects the general taste, but saponin can be destroyed and partially eliminated under high temperature, thereby resulting in less bubbles and reducing the bitter tone. Besides, soy beans contain a large amount of unsaturated fatty acids and various enzymes such as lipoxidase catalyzing fat oxidation, and thus forming substances carrying the so called beany flavor. Destroying enzymes can inactivate lipoxidase and isoenzymes and can therefore suppress enzymatic reactions and thus the formation of substances carrying beany flavor.

In the present invention, by means of re-boiling, saponin is more significantly destroyed, thus minimizing the bitterness and improving the taste. By reducing bubbles, enzymes and micro bacteria especially those left on the bubbles after the soy liquid is boiled for the first time are thoroughly and completely destroyed. The safe and thorough handling of enzymes and micro bacteria can improve the stability of product quality during storage, thereby lengthening the preservation period of the product.

(2) Richer taste. Soy bean skin contains soybean polysaccharides which can be released more from the soy bean skin after re-boiling so that the soy milk can have a richer taste and a higher nutritional value. Re-boiling can also produce more flavoring substances like aldehydes to enrich the aroma of the soy milk.

FIG. 1 is a schematic view showing the structure of the soy bean soaking device of the present invention.

FIG. 2 is a schematic view showing the structure of the grinding device of the present invention.

In the figures: 1 denotes the constant temperature soy bean soaking tank; 11 denotes the cover; 111 denotes the material inlet; 112 denotes the water inlet; 113 denotes the air vent cap; 114 denotes the observation manhole; denotes the CIP cleaning nozzle; 116 denotes the driving device; 117 denotes the connection shaft; 12 denotes the body; 121 denotes the material outlet pipe; 122 denotes the soy bean blocking net; 123 denotes the nitrogen inlet; 124 denotes the first pneumatic valve; denotes the second pneumatic valve; 2 denotes the constant temperature heating device; 21 denotes the pipe heater; 22 denotes the steam inlet; 23 denotes the iced water inlet; 24 denotes the steam processing valve assembly; 3 denotes the constant temperature water storage tank; 31 denotes the CIP cleaning nozzle; 32 denotes the water outlet pipe; 321 denotes the sewage discharge opening; 322 denotes the water supply opening; 33 denotes the water inlet pipe; 331 denotes the backf low port; 4 denotes the thermometer; denotes the pump; 6 denotes the grinder; 61 denotes the seat; 62 denotes the casing; 63 denotes the liquid outlet tube; 64 denotes the gas and water inlet; denotes the water inlet; 66 denotes the material feeding tube; 7 denotes the liquid storage tank; 71 denotes the tank cover; 711 denotes the observation manhole; 712 denotes the air vent cap; 713 denotes the gas and water inlet; 72 denotes the tank body; 73 denotes the liquid outlet; 8 denotes the bean storage tank; 81 denotes the tank body; 82 denotes the tank bottom; 821 denotes the material outlet end; 83 denotes the water inlet; 9 denotes the separator; 91 denotes the cover 92 denotes the separator body; 93 denotes the filter net; 94 denotes the bean water inlet end; denotes the bean outlet end; 96 denotes the water outlet end; denotes the spiral material feeder.

In order to further describe the technical scheme of the present invention, the present invention is described in detail below with reference to an embodiment.

(I) A method of preparing a re-boiled soy milk, comprising the following steps: (1) Initial preparation: a. Selecting soy beans: select large and plump organic soy beans which are free of mould and impurities or which have only a small amount of impurities; b. Removing impurities: remov impurities in the soy beans by one or more than one of the following methods: winnowing, magnetic separation and specific gravity sorting.

c. Soaking: soaking the soy beans of step (b) in a soy bean soaking tank under constant temperature for a predetermined time duration; specifically, soaking is performed at a ratio of soy beans to water of 1: (1.8-3.5), a temperature of 2028°C, and a time duration of 6-8 hours; preferably, the ratio of soy beans to water is 1: (2.5-3.0); after soaking the soy beans, the water for soaking the soy beans is poured out; clean water is then poured in to rinse the soy beans, which are then ready to be used.

Specifically, feed materials via a material inlet into a constant temperature soy bean soaking tank which is connected and in communication with a constant temperature water storage tank via a pipeline system, wherein an amount of the materials being fed is determined by a ratio of soy beans to water for soaking; when a thermometer provided at a water outlet end of a constant temperature heating device connected to a pipe section between the constant temperature water storage tank and the constant temperature soy bean soaking tank shows a temperature which meets a predetermined temperature required for soaking the soy beans, pure water is filled into the constant temperature soy bean soaking tank; after feeding of materials into the constant temperature soy bean soaking tank, amounts of soy beans and water in the constant temperature soy bean soaking tank meet a predetermined beans to water ratio required; when soaking the soy beans, the constant temperature soy bean soaking tank is maintained in a sealed condition; a nitrogen supply device connected and in communication with the constant temperature soy bean soaking tank via a pipeline system supplies nitrogen into the constant temperature soy bean soaking tank, thus the constant temperature soy bean soaking tank is filled with nitrogen, and oxygen inside is expelled. Stir the soy beans with nitrogen once an hour. After a predetermined period of soaking under constant temperature, the soy beans can be released.

d. Grinding: adding in an appropriate amount of water to the organic soy beans which have been soaked in step (c), grinding the soy beans by means of stone milling to obtain soy liquid; specifically, grinding is performed at a ratio of soy beans to water of 1: (3.8-6.5), preferably 1 (4.5-5.2); More specifically, assure that a grinder is cleaned and a stone mill is assembled appropriately; adjust the gap between the stone mill and the millstone according to the grain sized required and set the grinding water pressure to exceed 1kg (i.e. 0.1 MPa). Set the grinding water temperature according to the soy milk processing requirement, and set the nitrogen pressure to exceed 1kg (i.e. 0.1 MPa). Furthermore, after the soy beans are soaked, the bean water passes through an upper portion of the bean storage tank and is drained by the separator connected and in communication with the bean storage tank. The soy beans enter via the material inlet of the bean storage tank to the bean storage tank for storage, wherein the bean storage tank has a bean outlet end which is connected and in communication with the grinder via the spiral material feeder and a pipeline system sequentially. Adjust the valve open level of the bean storage tank and the water flow rate of the water supply connected and in communication with the material feeding tube of the grinder. Pure water supplied by the water supply enters the grinder via the material feeding tube of the grinder at a beans to water ratio required for grinding according to production needs. The beans in the bean storage tank enters the spiral material feeder whose input end is connected and in communication with the material outlet end of the bean storage tank and whose output end is connected and in communication with the grinder. The beans are fed at a fixed quantity by the spiral material feeder to the grinder via the material feeding tube of the grinder. At the same time, switch on the nitrogen supply device connected and in communication with the grinder via a pipeline system. Nitrogen passes through the CIP cleaning tube to fill the grinder with nitrogen and expel oxygen from the grinder. Then switch on the grinder to perform grinding. The stone mill grinds the soy beans. During grinding, the grinder is controlled to maintain at a sealed condition. After the grain size of the liquid meets the predetermined processing requirement, grinding is completed.

(2) Boiling: heating up the soy liquid under normal pressure to 70-80°C, and then boiling the heated up soy liquid under micro pressure which is 0.03MPa0.08MPa for 5-10 minutes to obtain a boiled soy liquid.

(3) Separating: pressing the boiled soy liquid to separate a majority of bean dregs from the soy liquid; wherein a filter net used for separating the bean dregs has a mesh hole diameter of 0.35-0.6mm.

(4) Re-boiling: keeping the boiled soy liquid with the bean dregs separated at 8595°C, and then re-boiling the soy liquid under micro pressure which is 0.03MPa-0.08MPa for 5-10 minutes to obtain a re-boiled soy liquid.

(5) Centrifugal separating: subjecting the re-boiled soy liquid to high speed centrifugation at a speed of 3600-4500r/min to eliminate residues, thereby obtaining a soy milk.

(6) Cooling: cooling the soy milk quickly by using a plate-type heat exchanger at a cooling temperature of 2-3°C, and the soy milk is eventually cooled down to 415°C.

(7) Standardizing index: detecting a protein index of the cooled down soy milk of step (6), and then adjusting its protein contents to 2.5-4.5% by methods such as dilution; It should be noted that, before proceeding to the following steps (8) and (9), bag-type filtering using a filter net having 100-300 meshes can be performed after step (7) so as to remove impurities such as fibers that have diameters not able to pass through the meshes, thereby increasing the stability of the soy milk after filtering.

(8) Sterilizing: sterilizing the soy milk after index standardization by UHT sterilization under 137-142°C for 5-35 seconds.

(9) Sterile packaging: filling the soy milk sterilized by UHT sterilization into packaging bottles.

It should be noted that, the soy beans can be selected from other types of soy beans currently available in the market, but preferably the above mentioned organic soy beans. The present invention makes use of a soy bean soaking device and a grinding device as described below for soaking the soy beans and grinding the soy beans.

Nitrogen charging may be performed according to practical situation during the processes of soaking and grinding.

The method of preparing a re-boiled soy milk according to the present invention is advanced and reasonable, and can be implemented easily. Also, the production of soy milk is effective and the product is hygienic. The method of the present invention is obviously better than the conventional method of preparing soy milk. The soy milk made according to the method of the present invention has a higher nutritional value, longer preservation period, and is safer to consume. The soy milk made by the method of the present invention has an obviously much better quality than conventional soy milk, and has a richer taste The method of the present invention has the following beneficial effects: 1. Safer and more hygienic, and has a longer preservation period. Soy beans contain saponin which forms bubbles. Bubbles have poor heat conductivity. Therefore, after soy liquid is boiled for the first time, substances especially like enzymes and micro bacteria on the bubbles may not be completely killed and destroyed due to insufficient heat caused by poor heat conductivity. Accordingly, there is a risk of unhygienic and unsafe food. Also, saponin has a bitter tone that affects the general taste, but saponin can be destroyed and partially eliminated under high temperature, thereby resulting in less bubbles and reducing the bitter tone. Besides, soy beans contain a large amount of unsaturated fatty acids and various enzymes such as lipoxidase catalyzing fat oxidation, and thus forming substances carrying the so called beany flavor. Destroying enzymes can inactivate lipoxidase and isoenzymes and can therefore suppress enzymatic reactions and thus the formation of substances carrying beany flavor.

By means of re-boiling, saponin is more significantly destroyed, thus minimizing the bitterness and improving the taste. By reducing bubbles, enzymes and micro bacteria especially those left on the bubbles after the soy liquid is boiled for the first time are thoroughly and completely destroyed. The safe and thorough handling of enzymes and micro bacteria can improve the stability of product quality during storage, thereby lengthening the preservation period of the product.

2. Richer taste. Soy bean skin contains soybean polysaccharides which can be released more from the soy bean skin after re-boiling so that the soy milk can have a richer taste and a higher nutritional value. Re-boiling can also produce more flavoring substances like aldehydes to enrich the aroma of the soy milk product.

3. Soy beans are soaked under a sealed environment having a constant temperature to decrease soaking time and thus achieving a higher efficiency of soy bean soaking. It is easier to control the time needed for soaking. Also, the soy bean soaking tank is effectively sealed to prevent contact with the surrounding environment so as to be free of pollutants. Furthermore, the soy bean soaking tank can prevent oxygen from getting inside, and so the growth of micro bacteria especially moulds can be suppressed.

4. Soy liquid is boiled under micro positive pressure to slightly increase the boiling point of the liquid. The boiling temperature is increased and the time for boiling is shortened on condition that the nutrients of the soy liquid are preserved as much as possible. Moreover, the temperature for destroying enzymes and micro bacteria is increased so that enzymes and micro bacteria are more thoroughly eliminated to increase the efficiency of destroying the enzymes and micro bacteria.

5. Bag-type filtering after index standardization can ensure the stability of the ingredients of the soy milk, impose strict control on the diameter of the ingredients, and thus ensure soft and smooth taste of the soy milk.

6. Organic soy bean ensures safety of the product from selection of raw materials. It is also worth developing a kind of nutritious, safe, green and healthy soy milk in the market, for example, it is very suitable for instant consumption during breakfast and is portable for carrying.

(II) Soy bean soaking device The present invention uses a nitrogen charging soy bean soaking device, comprising a constant temperature soy bean soaking tank 1, a constant temperature heating device 2 and a constant temperature water storage tank 3. The constant temperature soy bean soaking tank 1, the constant temperature heating device 2 and the constant temperature water storage tank 3 are connected and in communication with one another through pipes. Pure water is temporarily stored in the constant temperature water storage tank 3. During use, the water in the constant temperature water storage tank 3 will be quickly heated by the constant temperature heating device 2 and then supplied to the constant temperature soy bean soaking tank 1. In the present invention, the constant temperature soy bean soaking tank 1 and the constant temperature water storage tank 3 are double layered thermo tanks which have the function of thermal insulation so as to maintain the temperature during soaking of the soy bean.

The constant temperature soy bean soaking tank 1 comprises a cover 11 and a body 12. The cover 11 is connected with the body 12 by a buckling structure so that the cover can be opened or closed with respect to the body 12. The cover 11 is provided with an observation manhole 114, a clean-in-place (CIP) cleaning nozzle 115, a material inlet 111 in communication with the body 12, a water inlet 112 in communication with the body 12, and an air vent cap 113 in communication with the body 12. The observation manhole 114 is disposed on the cover 11 in a sealed manner, and a manhole cover is correspondingly provided on the observation manhole. A bottom part of the body 12 is provided with a material outlet pipe 121 and a soy bean blocking net 122 that selectively blocks the material outlet pipe 121. The material outlet pipe 121 is in communication with the body 12. A driving device 116 which drives the soy bean blocking net 122 to move up and down is provided at a center position of a top part of the cover 11. An output end of the driving device 116 is connected with one end of a connection shaft 117, and another end of the connection shaft 117 is fixed with the soy bean blocking net 122, so that the soy bean blocking net 122 can be driven up by the driving device 116 to release the soy beans, or be driven down to block the material outlet pipe 121 for soaking the soy beans. The driving device 116 is a piston driving device commonly available in the industry. The material inlet 111 allows feeding of a predetermined amount of soy beans. The air vent cap 113 maintains a balance of pressure inside and outside the constant temperature soy bean soaking tank 1. The observation manhole 114 allows a user to observe the conditions inside the constant temperature soy bean soaking tank 1. The material outlet pipe 121 releases a mixture of water and soaked soy beans. The soy bean blocking net 122 has a shape and size matching with a cross-sectional shape and a diameter of the material outlet pipe 121. The soy bean blocking net 122 consists of a plurality of evenly distributed meshes thereon. Each of the meshes of the soy bean blocking net 122 has a diameter smaller than that of each soy bean.

The material outlet pipe 121 of the body 12 is provided with a nitrogen inlet 123 which is in communication with the body 12. A nitrogen supply device is provided external to the constant temperature soy bean soaking tank 1. The nitrogen supply device is connected and in communication with a nitrogen inlet 123 of the material outlet pipe 121 through a pipe provided with a pneumatic valve and a one way valve. The material outlet pipe 121 of the body 12 is provided with a first pneumatic valve 124, a second pneumatic valve 125 and a hand-operated valve. The nitrogen inlet 123 is positioned between the first pneumatic valve 124 and the second pneumatic valve 125. The first pneumatic valve 124 is positioned above the second pneumatic valve 125. The second pneumatic valve 125 is positioned above the hand-operated valve. During operation, when the hand-operated valve is open, and the first pneumatic valve 124 is open while the second pneumatic valve 125 is close, nitrogen from the nitrogen supply can enter the constant temperature soy bean soaking tank 1 from the nitrogen inlet 123 through the material outlet pipe 121 so as to replace air in the constant temperature soy bean soaking tank 1 before soaking the soy beans, or to expel oxygen, turn and stir the beans during the soaking process. During the process of soaking the soy beans, the cover 11 is always closed and sealed to maintain the nitrogen inside the body 12. Further, when the first pneumatic valve 124 and the second pneumatic valve 125 are both open, and the soy bean blocking net 122 blocks the material outlet pipe 121, the constant temperature soy bean soaking tank 1 can release water alone. When the first pneumatic valve 124 and the second pneumatic valve 125 are both open, and the soy bean blocking net 122 is lifted up, both water and soy beans can be released from the constant temperature soy bean soaking tank 1.

The body 12 comprises a cylindrical main body and a funnel shaped bottom connected with each other as a whole. An inner side wall of the cylindrical main body of the body 12 is provided with two liquid level sensors correspondingly positioned at an upper portion and a lower portion of the cylindrical main body respectively. The two liquid level sensors comprise an upper liquid level sensor and a lower liquid level sensor. When liquid level is lower than the lower liquid level sensor, a control system of the present invention supplies water to the constant temperature soy bean soaking tank 1 automatically through the water inlet 112. When liquid level is higher than the upper liquid level sensor, the control system automatically stops supplying water to the constant temperature soy bean soaking tank 1 through the water inlet 112.

Further, a center position of a top part of the constant temperature water storage tank 3 is provided with a CIP cleaning nozzle 31 so that clean-in-place operation can take place inside the water storage tank. An upper side of the constant temperature water storage tank 3 is provided with a water inlet pipe 33 in communication with the constant temperature water storage tank 3. The water inlet pipe 33 is provided with a backf low port 331 in communication with the constant temperature water storage tank 3. A lower side of the constant temperature water storage tank 3 is provided with a water outlet pipe 32 in communication with the constant temperature water storage tank 3. The water outlet pipe 32 is provided with a sewage discharge opening 321 and a water supply opening 322. The water supply opening 322 of the constant temperature water storage tank 3 is connected and in communication with the water inlet 112 of the constant temperature soy bean soaking tank 1 through a pipeline. The constant temperature heating device 2 is mounted on the pipeline. Besides, a water pump 5 is also mounted on the pipeline between the constant temperature water storage tank 3 and the constant temperature heating device 2. The water pump 5 is mounted on the pipeline corresponding to a water inlet end of the constant temperature heating device 2, so as to pump water from the constant temperature water storage tank 3 to the constant temperature heating device 2 for heating. Further, heated water is pumped to the constant temperature soy bean soaking tank 1 through the water inlet 112, or pumped back to the constant temperature water storage tank 3 through the backflow port 331. Also, a thermometer 4 having a temperature probe is mounted on the pipeline corresponding to a water outlet end of the constant temperature heating device 2 to monitor temperature of heated pure water in the pipeline. An output end of the pipeline on which the thermometer 4 is mounted is in communication with the water inlet 112 of the constant temperature soy bean soaking tank 1 as well as in communication with the backflow port 331 of the water inlet pipe 33 via another pipeline. Said another pipeline is mounted with a one way valve proximal to the backflow port 331 to prevent water from the water inlet pipe 33 from backflowing into said another pipeline. Accordingly, a circulation circuit is formed between the constant temperature water storage tank 3 and the constant temperature heating device 2. Specifically, the pipe at one end (i.e water inlet end) of the constant temperature heating device 2 is connected and in communication with the water supply opening 322 of the constant temperature water storage tank 3; the pipe at another end (i.e. water outlet end) of the constant temperature heating device 2 is connected and in communication with the backflow port 331 of the water inlet pipe 33 of the constant temperature water storage tank 3. Besides, the pipe at said another end (i.e. water outlet end) of the constant temperature heating device 2 is also connected and in communication with the water inlet 112 of the constant temperature soy bean soaking tank 1.

When the thermometer 4 detects that the water temperature of the water heated by the constant temperature heating device 2 is higher or lower than a temperature required for production, water in the pipeline will flow back to the constant temperature water storage tank 3 via said circulation circuit. By contrast, if the water temperature detected by the thermometer 4 meets the temperature required for production, water in the pipeline enters into the constant temperature soy bean soaking tank 1 via the water inlet 112 of the constant temperature soy soaking tank 1.

Further, the constant temperature heating device 2 uses a heat exchanger. The heat exchanger comprises a pipe heater 21. A steam inlet 22 and an iced water inlet 23 oppositely arranged with respect to each other are disposed above the pipe heater 21. The steam inlet 22 and the iced water inlet 23 are both connected with an inlet pipe which is in communication with the pipe heater 21. In other words, the steam inlet 22 and the iced water inlet 23 are both in communication with the pipe heater 21. A steam supply is mounted on the constant temperature heating device 2 corresponding to the steam inlet 22; an iced water supply is mounted also on the constant temperature heating device 2 corresponding to the iced water inlet 23. The steam supply is in communication with the steam inlet 22 of the pipe heater 21 via a pipeline system mounted with a steam processing valve assembly 24. The iced water supply is in communication with the iced water inlet 23 of the pipe heater 21 via another pipeline system. A sewage discharge pipe and an iced water backf low pipe are disposed below the pipe heater 21. The sewage discharge pipe can be used for discharging condensated water. The iced water backf low pipe is used for collecting iced water for recycled use in order to achieve energy conservation and environmental friendliness. A connection pipe is provided between the sewage discharge pipe and the iced water backflow pipe. A jet tube is provided inside the pipe heater 21. Heated pure water is instantly and effectively mixed with steam/iced water in the jet tube under high flowing speed, so that heated pure water and steam/iced water are thoroughly mixed, and total heat exchange is achieved. By adjusting the mixing ratio of the heated pure water and steam/iced water, a liquid having a required temperature can be obtained. The steam supply system and its heat exchange with the pipe heater 21 are common prior arts.

The steam processing valve assembly 24 comprises a first pressure gauge, a hand operated ball valve, a gas stop valve, a pressure reduction valve, a second pressure gauge, a safety valve and a pneumatic ball valve which are sequentially arranged on a pipe section between the steam supply and the steam inlet 22 of the pipe heater 21 proximal to the steam inlet 22. A hand operated valve, a liquid stop valve, a thermometer and a pressure gauge are sequentially arranged along a pipe section between the iced water supply and the iced water inlet 23 of the pipe heater 21 proximal to the iced water inlet 23.

It should be understood that, apart from using the aforesaid heat exchanger for heating, the present invention can also use other heating methods such as electrical heating. Besides, the control system of the present invention is a common control system used in the prior arts. Along the pipelines which the constant temperature soy bean soaking tank 1, the constant temperature heating device 2 and the constant temperature water storage tank 3 are connected and in communication with one another, an input end and an output end of each element are each provided with a pneumatic valve and/or hand operated valve, so that a pipe can be opened or closed based on practical production situation. Positioning of all the pneumatic valves and/or hand operated valves is determined according to the working principle of ordinary production equipment, thereby fulfilling the operation requirements of ordinary prior arts, and is therefore not detailed herein.

The present invention uses a nitrogen charging soy bean soaking device and achieves fully automatic production. The present invention uses a constant temperature soy bean soaking tank 1 and a nitrogen supply device. The constant temperature soy bean soaking tank 1 is a double layer composite thermo tank, which can soak the soy beans under constant temperature, thereby maintaining the consistency regarding the time and temperature of soaking different batches of soy beans throughout the entire year, and thus capable of controlling the consistency regarding expansion of soy beans of different batches. Also, the constant temperature soy bean soaking tank 1 soaks the soy beans in a sealed condition, thereby reducing secondary pollution caused by microorganisms during the process of soaking the soy beans. Besides, since oxygen outside the tank is isolated under sealed condition, the growth of aerobic micro-organisms inside the tank can be controlled. The nitrogen supply device supplies nitrogen to the constant temperature soy bean soaking tank 1; before soaking the soy beans, the constant temperature soy bean soaking tank 1 is filled with nitrogen to replace the air originally inside the tank so that oxygen is expelled from the tank. During the process of soaking the soy beans, intermittently fill the tank with nitrogen to expel oxygen so as to suppress the growth of aerobic micro-organisms, suppress lipid oxidation of the soy beans and thus suppress the formation of substances having beany flavors. As such, the subsequent soy bean product will have an improved taste. By stirring and turning the soy beans in the tank with nitrogen from a compressor, spaces between the beans are widen such that the beans will not press against one another over a long period of time. As such, the beans can absorb water more evenly. Stirring allows the water that soaks the beans to have a more uniform temperature, such that the beans in the same tank can expand with a more uniform speed and degree of expansion. Stirring can be performed once an hour.

(III) Grinding device The present invention uses a nitrogen charging grinding device. As shown in FIG. 2, the grinding device comprises a grinder 6, a liquid storage tank 7, a bean storage tank 8 and a separator 9 for separating beans and water. The separator 9 is disposed above the bean storage tank 8. The separator 9, the bean storage tank 8, the grinder 6 and the liquid storage tank 7 are sequentially connected and in communication with one another via pipes. In the description below, the term "bean water" refers to a mixture of soaked beans and water soaking the beans.

The separator 9 comprises a sealed cover 91 and separator body 92 having a scraper hopper shape. The sealed cover 91 is fixed at a periphery of a mouth of the separator body 92 via a buckling structure so that the sealed cover 91 can be opened or closed with respect to the separator body 92. The separator body 92 is hollow inside forming a cavity. In the cavity, a filter net 93 is fixed to the walls of the cavity at a middle position of the cavity along a longitudinal direction of the separator 9, and thus separating the separator 9. The filter net 93 is used for separating bean water, which means a mixture of soy beans and water soaking the beans. The separator body 92 has a depth which gradually increases from top to bottom. An upper side wall of the separator body 92 is provided with a bean water inlet end 94; a lower side wall of the separator body 92 is provided with a bean outlet end 95. The bean water inlet end 94 and the bean outlet end 95 are oppositely arranged. Also, a water outlet end 96 is provided at the deepest position of the separator body 92. The separator 9 is disposed above the bean storage tank 8 in a tilted manner, such that a plane where the mouth of the separator body 92 is positioned forms an included angle of 30-50 degrees, preferably 45 degrees, with respect to a horizontal plane, in order to facilitate quick separation and filtering of the bean water. The bean water inlet end 94 is connected and in communication with the material outlet pipe 121 of the soy bean soaking device via a pipe. The bean outlet end 95 of the separator 9 is connected with a material inlet of the bean storage tank 8 via a pipe. Bean water after entering into the separator 9 will have the water soaking the beans being filtered by the filter net 93. After water is drained away, the soy beans are released through the bean outlet end 95 of the separator 9, and then the soy beans enter and are stored in the bean storage tank 8 through the material inlet of the bean storage tank 8. The water soaking the beans is discharged through the water outlet end 96 disposed at the deepest position of the separator body 92.

The bean storage tank 8 is a hollow tank. The bean storage tank 8 comprises a cylindrical tank body 81 and a funnel shaped tank bottom 82 connected with each other as a whole. A top side of the tank body 81 is sealed with a cover. The cover of the tank body 81 is provided with the material inlet and a water inlet 83, both of which being in communication with an interior of the bean storage tank 8. The water inlet 83 is connected and in communication with a water supply via a pipeline system. The tank bottom 82 is provided with a material outlet end 821 The material outlet end 821 is connected with a spiral material feeder 10. The material outlet end 821 is also provided with a bean valve. The bean valve can be adjusted to partially open in order to control the amount of the beans being released. The material outlet end 821 is connected and in communication with an input end of the spiral material feeder 10. The input end of the spiral material feeder 10 is oriented upwardly. The grinder 6 is mounted below the bean storage tank 8.

An inner side wall of the tank body 81 is provided with two detectors mounted at different heights of the tank body for detecting the amount of soy beans stored inside the bean storage tank 8. The two detectors comprise a panel shape upper detector and a panel shape lower detector disposed at an upper portion of inner side wall and a lower portion of the inner side wall respectively. When the amount of soy beans falls below the lower detector, a control system of the present invention will automatically feed in material into the bean storage tank 8 via the material inlet of the bean storage tank 8. When the amount of soy beans exceeds the upper detector, the control system automatically stops feeding material into the bean storage tank 8 via the material inlet of the bean storage tank 8.

The grinder 6 comprises a seat 61 and a casing 62. A stone mill and a millstone rotatable with respect to each other are disposed inside the casing 62, and a gap between the stone mill and the millstone is adjustable. The millstone is fixed on the seat 61. The stone mill is disposed on the millstone and rotatable with respect to the millstone. Preferably, the grinder 6 adjusts the gap between the stone mill and the millstone by rotatably adjusting the height of the stone mill above the millstone via a driving device in order to adjust the grain size. A motor is provided on the seat 61. An output shaft of the motor is connected with a rotation shaft of the stone mill to achieve motion transmission via motion transmission mechanism such as transmission gears and chains etc. such that the stone mill is driven to rotate. Further, soy beans are transferred from the bean storage tank 8 to the casing 62 sequentially through the spiral material feeder 10 and a material feeding tube 66. The stone mill crushes and grinds the soy beans. The material feeding tube 66 and a gas and water inlet 64 are provided in communication with the grinder 6. The material feeding tube 66 and the gas and water inlet 64 are in communication with the casing 62 respectively. The material feeding tube 66 is disposed above the grinder 6. The material feeding tube 66 is connected and in communication with an output end of the spiral material feeder 10. The output end of the spiral material feeder 10 is oriented downwardly. The material feeding tube 66 is further provided with a water inlet 65 which is in communication with the grinder 6. The water inlet 65 is connected and in communication with a water supply via a pipeline system. The water inlet 65 is used for supplying water in order to adjust the beans to water ratio for grinding. Furthermore, the gas and water inlet 64 is connected and in communication with a water supply and a nitrogen supply device as detailed below via a pipeline system respectively. In this way, a pipe which is in communication with the gas and water inlet 64 may be used as a CIP cleaning pipe; a water outlet end of the CIP cleaning pipe is provided with a CIP cleaning nozzle which is positioned at a top portion inside the grinder 6. Water passing through the CIP cleaning pipe is discharged from the CIP cleaning nozzle to perform CIP cleaning inside the grinder 6. Nitrogen passing through the CIP cleaning pipe is discharged from the CIP cleaning nozzle to enter the grinder 6. In other words, the gas and water inlet 64 is used for supplying nitrogen or CIP cleaning.

A nitrogen supply device is provided external to the grinder 6. The nitrogen supply device comprises a nitrogen supply, a compressor and a gas filter which are sequentially connected with each other. The gas filter is connected and in communication with the gas and water inlet 64 via a pipe provided with a pneumatic valve and a one way valve. During grinding, when the pneumatic valve and the one way valve are both open, nitrogen supplied by a nitrogen supply enters the grinder 6 via the gas and water inlet 64 to fill the grinder 6 with nitrogen and expel oxygen. After the soy beans are grinded, their substances such as lipoxidase are completely released; filling nitrogen and expelling oxygen may stop the grinded soy beans which release lipoxidase to undergo fat oxidation, thereby suppressing formation of substances carrying beany flavor. The grinder 6 is further provided with a liquid outlet tube 63 which is in communication with the casing 62. The liquid outlet tube 63 is correspondingly arranged below the material feeding tube 66. The output end of the spiral material feeder 10 and the material feeding tube 66 of the grinder 6 are connected and in communication with each other. Feeding speed may be controlled by setting rotation speed of the spiral material feeder 10.

The motor on the seat 61 may control the rotation speed of the stone mill during grinding, i.e. the grinding speed. Besides, the present invention may adjust the grain size by adjusting the gap between the stone mill and the millstone. The grain size affects the taste of subsequent soy milk. It should be noted that the mechanism for adjusting the gap between the stone mill and the millstone is conventional in the stone mill industry and is therefore not detailed herein.

The liquid storage tank 7 comprises a tank cover 71 and a tank body 72. The tank cover 71 is connected with the tank body 72 by a buckling structure so that the tank cover can be opened or closed with respect to the tank body. The tank cover 71 is provided with an observation manhole 711, an air vent cap 712 and a gas and water inlet 713 The air vent cap 712 maintains a balance of pressure inside and outside the liquid storage tank 7. The observation manhole 711 allows a user to observe the conditions inside the tank. The gas and water inlet 713 is connected and in communication with a water supply and a nitrogen supply device via a pipeline system. In this way, the gas and water inlet 713 may be used as a CIP cleaning pipe; the CIP cleaning pipe is provided with a CIP cleaning nozzle which is positioned at a top portion inside the liquid storage tank 7. Water passing through the CIP cleaning pipe is discharged from the CIP cleaning nozzle to perform CIP cleaning inside the liquid storage tank 7. Nitrogen passing through the CIP cleaning pipe is discharged from the CIP cleaning nozzle to enter the liquid storage tank 7. In other words, the gas and water inlet 713 is used for supplying nitrogen or CIP cleaning. The nitrogen supply device of the liquid storage tank 7 may be the nitrogen supply device of the grinder 6, so that both use the same nitrogen supply device. Nitrogen may enter the liquid storage tank 7 via the gas and water inlet 713 to fill the liquid storage tank 7 with nitrogen and expel oxygen, thereby suppressing formation of substances carrying beany flavor in the soy liquid. It should be noted that during operation of the devices of the present invention, the grinder 6 and the liquid storage tank 7 are both sealed. Besides, nitrogen charging of the grinding device during operation may be adjusted and controlled according to production needs and may vary depending on different soy milk preparation methods, thus it has good flexibility.

The water inlet 83, the water inlet 65, the gas and water inlet 64 and the gas and water inlet 713 may share the same water supply and correspondingly connected and in communication with the same pipeline system. The liquid storage tank 7 is provided with a liquid inlet which is connected and in communication with the liquid outlet tube 63 of the grinder 6. The liquid inlet is positioned at a height which is relatively lower than the position where the liquid outlet tube 63 is mounted for facilitating transfer of liquid. The tank body 72 is provided with a liquid outlet 73 at its bottom. The liquid outlet 73 is connected and in communication with a boiling device in the soy bean production line via a pipeline system. An inner side wall of the tank body 72 is provided with two liquid level sensors mounted at different heights of the tank body, which are an upper liquid level sensor and a lower liquid level sensor respectively. The upper liquid level sensor is provided at an upper portion of the tank body 72; the lower liquid level sensor is provided at a lower portion of the tank body 72. The upper liquid level sensor and the lower liquid level sensor are used for detecting liquid level of the liquid inside the liquid storage tank 7.In this way, when liquid level is lower than the lower liquid level sensor, a control system of the present invention supplies liquid to the liquid storage tank 7 automatically through the liquid inlet of the liquid storage tank 7. When liquid level is higher than the upper liquid level sensor, the control system automatically stops supplying liquid to the liquid storage tank 7 through the liquid inlet of the liquid storage tank 7.

It should be noted that each element along the connecting pipelines is provided with a pneumatic valve and/or hand operated valve, so that a pipe can be opened or closed, as well as the flow rates and the open level of the bean valves may be adjusted based on practical production situation. Positioning of all the pneumatic valves and/or hand operated valves is determined according to the working principle of ordinary production equipment, thereby fulfilling the operation requirements of ordinary prior ads, and is therefore not detailed herein. Besides, the control system of the present invention is a common control system used in the prior arts. The upper liquid level sensor, the lower liquid level sensor, and the panel shape upper detector and the panel shape lower detector are all available in the prior ads, and thus the structure and assembly thereof are not detailed herein.

When the nitrogen charging grinding device of the present invention is in use, the soaked beans and water soaking the beans, i.e. the bean water, enter the separator 9. The water soaking the beans are filtered by the separator 9, and the beans after draining enter the bean storage tank 8. The beans in the bean storage tank 8 are transferred to the grinder 6 via the spiral material feeder 10. After the grinder 6 grinds the beans to liquid, the liquid is fed to the liquid storage tank 7 and is ready for use.

The nitrogen charging grinding device of the present invention achieves fully automatic production. The nitrogen supply device supplies nitrogen to the grinder 6 and/or the liquid storage tank 7. With the use of the nitrogen supply device to supply nitrogen and expel oxygen, lipid oxidation of the unsaturated fatty acid of the soy liquid obtained after grinding may be suppressed, thus suppressing the formation of substances having beany flavors, and improving the taste of the subsequent soy bean product.

Further, stone mill is used in the grinding device of the present invention, and the gap between the stone mill and the millstone may be adjusted, thereby adjusting the grain size. The rotation speed of the stone mill during grinding is slower, thus the resulting soy milk maintains the flavor and taste of the soy beans to a great extent, and has good nutrition value. Besides, use of the stone mill results in smoother product which is richer in taste and maintains various trace elements of the soy bean product. In comparison with the prior art, the present invention prevents destruction of the nutrients by the high temperature and high pressure processing of conventional large scale machine production.

It should be noted that nitrogen charging of the soaking and grinding devices of the present invention during operation may be adjusted and controlled according to production needs and may vary depending on different soy milk preparation methods, thus it has good flexibility.

The above embodiment and the accompanying drawings are not intended to limit the form of the processing method and apparatus of the present invention; any suitable changes or modifications made by the persons skilled in the art should not be considered as departing from the scope of the present invention.

Claims

CLAIMS1. A method of preparing a re-boiled soy milk, characterized in that it comprises the following steps: (1) Initial preparation: Remove impurities in raw soy beans to obtain soy beans; soak the soy beans in a constant temperature soy bean soaking tank under constant temperature for a predetermined time duration; during soaking, feed materials via a material inlet into the constant temperature soy bean soaking tank which is connected and in communication with a constant temperature water storage tank via a pipeline system, wherein an amount of the materials being fed is determined by a ratio of soy beans to water for soaking; when a thermometer provided at a water outlet end of a constant temperature heating device connected to a pipe section between the constant temperature water storage tank and the constant temperature soy bean soaking tank shows a temperature which meets a predetermined temperature required for soaking the soy beans, pure water is filled into the constant temperature soy bean soaking tank; after feeding of materials into the constant temperature soy bean soaking tank, amounts of soy beans and water in the constant temperature soy bean soaking tank meet a predetermined beans to water ratio required; when soaking the soy beans, the constant temperature soy bean soaking tank is maintained in a sealed condition; a nitrogen supply device connected and in communication with the constant temperature soy bean soaking tank via a pipeline system supplies nitrogen into the constant temperature soy bean soaking tank, thus the constant temperature soy bean soaking tank is filled with nitrogen, and oxygen inside is expelled; stir the soy beans with nitrogen once an hour; after a predetermined period of soaking under constant temperature, the soy beans can be released; the soaked soy beans are grinded to obtain a soy liquid; (2) Boiling: heating up the soy liquid under normal pressure to 70-80°C, and then boiling the heated up soy liquid under micro pressure which is 0.03MPa-0.08MPa for 510 minutes to obtain boiled a soy liquid; (3) Separating: pressing the boiled soy liquid to separate bean dregs therefrom; wherein a filter net used for separating the bean dregs has a mesh hole diameter of 0.35-0.6mm; (4) Re-boiling: keeping the boiled soy liquid with the bean dregs separated at 8595°C, and then re-boiling the soy liquid under micro pressure which is 0.03MPa0.08MPa for 5-10 minutes to obtain a re-boiled soy liquid; (5) Centrifugal separating: subjecting the re-boiled soy liquid to high speed centrifugation at a speed of 3600-4500r/min to eliminate residues, thereby obtaining a soy milk; (6) Cooling: cooling down the soy milk to 4-15°C; (7) Standardizing index: detecting a protein index of the cooled down soy milk and then adjusting its protein contents to 2.5-4.5%.
2. The method of preparing a re-boiled soy milk as in Claim 1, characterized in that, it further comprises the following steps: (8) Sterilizing: sterilizing the soy milk after index standardization by UHT sterilization under 137-142°C for 5-35 seconds; (9) Sterile packaging: filling the soy milk sterilized by UHT sterilization into packaging bottles.
3. The method of preparing a re-boiled soy milk as in Claim 1, characterized in that, when soaking the soy beans in step (1), the soy beans are soaked in the constant temperature soy bean soaking tank at a temperature of 20-28°C for 6-8 hours.
4. The method of preparing a re-boiled soy milk as in Claim 1, characterized in that, grinding of the soy beans in step (1) is performed by stone milling.
5. The method of preparing a re-boiled soy milk as in Claim 1, characterized in that, the soy beans in step (1) are organic soy beans, and impurities in the soy beans are removed in step (1) by one or more than one of the following methods: winnowing, magnetic separation and specific gravity sorting.
6. The method of preparing a re-boiled soy milk as in Claim 1, characterized in that, after step (7), bag-type filtering of the soy milk using a filter net having 100-300 meshes is performed; sterilizing and sterile packaging are performed after filtering.
7. The method of preparing a re-boiled soy milk as in Claim 1, characterized in that, in step (1), a nitrogen charging soy bean soaking device is used for soaking the soy beans; the nitrogen charging soy bean soaking device comprises the constant temperature soy bean soaking tank, the constant temperature heating device and the constant temperature water storage tank; the constant temperature soy bean soaking tank, the constant temperature heating device and the constant temperature water storage tank are connected and in communication with one another through pipes; the constant temperature heating device is connected to a pipe section between the constant temperature soy bean soaking tank and the constant temperature soy bean water storage tank; a nitrogen supply device is provided external to the constant temperature soy bean soaking tank; the nitrogen supply device is connected and in communication with the constant temperature soy bean soaking tank through a pipe; Before soaking the soy beans, water in the constant temperature soy bean soaking tank is heated to a predetermined temperature by the constant temperature heating device for filling into the constant temperature soy bean soaking tank; during soaking, switch on the nitrogen supply device and intermittently fill the constant temperature soy bean soaking tank with nitrogen to expel oxygen, and stirring and turning the soy beans with nitrogen.
8. The method of preparing a re-boiled soy milk as in Claim 1, characterized in that, in step (1), a nitrogen charging grinding device is used for grinding; the nitrogen charging grinding device comprises a grinder, a liquid storage tank, a bean storage tank, a separator and a nitrogen supply device; the separator is disposed above the bean storage tank; the separator, the bean storage tank, the grinder and the liquid storage tank are sequentially connected and in communication with one another via pipes; the nitrogen supply device is connected and in communication with the grinder and the liquid storage tank respectively via pipes; After soaking, bean water enters the separator to filter out water soaking the beans, and the soy beans after draining enter the bean storage tank via a material inlet of the bean storage tank for storage; the soy beans in the bean storage tank is transferred to the grinder via a spiral material feeder which is connected between the bean storage tank and the grinder; during grinding, switch on the nitrogen supply device to supply nitrogen to the grinder and the liquid storage tank to fill the grinder and the liquid storage tank with nitrogen to expel oxygen; after the grinder grinds the soy beans to liquid, the liquid is fed to the liquid storage tank.