Solid malt extract spray freeze drying device and method capable of reducing dimethyl sulfide content

Abstract

The present invention relates to a solid malt extract spray freeze-drying device capable of reducing the content of dimethyl sulfide, which comprises an atomization system, a refrigeration system, a vacuum freezing system, a heating system and a control system. The atomization system includes an air compressor, a pressure atomizer, a pressure vessel and a material container. The air compressor is connected to the pressure vessel through a pressure transmission pipeline, and the pressure atomizer is connected to the pressure vessel through a material feeding pipeline. The refrigeration system includes a refrigerator, a condenser, a fan and a separation dust collector. The condenser and the fan are connected to the drying chamber through a cold air circulation pipeline. The vacuum pump of the vacuum system is connected to the drying chamber through a cold trap. The heating system is a heating partition plate and an electric heater at the bottom of the drying chamber. The preparation device of the present invention can remove the bad volatile sulfide dimethyl sulfide in the wort during the drying process, and prepare a solid malt extract powder with the dimethyl sulfide content completely removed. The reconstituted solid malt extract powder has an excellent flavor.

Description

Technical Field

[0001] The invention relates to the technical field of spray freeze drying, in particular to a solid malt extract spray freeze drying device and method capable of reducing the content of dimethyl sulfide. Background Art

[0002] Dry Malt Extract (DME) is a powder prepared by drying wort to remove moisture. Compared with wort that is easy to deteriorate, solid malt extract powder has excellent processing characteristics such as light resistance, heat resistance, and easy transportation. After re-dissolving, solid malt extract powder can be directly used for beer fermentation, or it can be flexibly added during beer preparation to adjust the concentration of wort. In the current craft beer market that pursues high quality and personalization, solid malt extract powder is in great demand.

[0003] At present, solid malt extract powder on the market is often produced by spray drying, but the high temperature environment of the spray drying process is easy to destroy the nutrients in the wort, and the prepared malt extract has the disadvantages of easy agglomeration and poor rehydration. A few solid malt extract powders are prepared by freeze drying, but the prepared freeze-dried malt extract needs secondary crushing, resulting in irregular powder shape and wide particle size distribution, poor powder fluidity and affecting packaging.

[0004] Spray freeze drying technology is a new powder preparation process that combines the advantages of spray drying and freeze drying. It prepares powdered solid products in a vacuum and low-temperature drying environment. Spray freeze drying can maintain the biological and chemical properties of the material, and the product can quickly recover to its pre-drying state after being dissolved in water. And because the atomization and freezing stage increases the surface area of ​​the frozen particles, it accelerates the heat and mass transfer during the drying process. Therefore, compared with freeze drying, it is advantageous to shorten the drying time and directly obtain powder particles with good fluidity.

[0005] Wort contains a volatile irritating sulfide called dimethyl sulfide, which has a boiling point of about 38°C and is not easily soluble in water. When the content of dimethyl sulfide in wort is too high, it will give the wort an unpleasant rotten corn smell. In an environment with a temperature higher than 70°C, the methylmethionine originally contained in the wort will continue to be thermally cracked to form dimethyl sulfide, so dimethyl sulfide will still remain in the wort after processing in a high temperature environment.

[0006] Currently, all commercially available solid malt extracts are prepared by factory-scale spray dryers. In the high-temperature closed environment of the spray drying process, thermal cracking reactions of methylmethionine with dimethyl sulfide are continuously produced in the wort droplets, resulting in a large amount of dimethyl sulfide remaining in the solid malt extract after preparation, seriously affecting the flavor of the solid malt extract after reconstitution. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a solid malt extract spray freeze drying device capable of reducing the dimethyl sulfide content. The drying process can remove the undesirable volatile sulfide dimethyl sulfide in the wort, and prepare a solid malt extract powder with extremely low dimethyl sulfide content. After the solid malt extract powder is re-dissolved, wort with excellent flavor can be obtained.

[0008] Another object of the present invention is to provide a spray freeze drying preparation method using the above-mentioned solid malt extract spray freeze drying device capable of reducing the dimethyl sulfide content.

[0009] The present invention solves the technical problem by the following technical solutions:

[0010] A spray freeze drying preparation device for solid malt extract powder with reduced dimethyl sulfide content, characterized in that it includes an atomization system, a refrigeration system, a vacuum freezing, a heating system and a control system, the atomization system includes an air compressor, a pressure atomizer, a pressure container and a material container, the air compressor is connected to the pressure container through a pressure transmission pipeline, the pressure atomizer is connected to the pressure container through a material transmission pipeline, the pressure atomizer outlet is located at the upper part of the material container, the material container is filled with liquid nitrogen, the pressure atomizer atomizes the material in the pressure container and sprays it into the material container and freezes it in the material container; the refrigeration system includes a refrigerator, a condenser, a fan and a separation dust collector, the refrigerant of the refrigerator is circulated back to the refrigerator through a first refrigerant liquid circulation pipeline winding around the condenser In the embodiment, the condenser and the fan are connected to the drying chamber through a cold air circulation pipeline; the vacuum system includes a vacuum pump, a cold trap and a drying chamber, the refrigerant of the refrigerator is circulated around the cold trap through a second refrigerant circulation pipeline and flows back to the refrigerator, and the cold trap is connected to the drying chamber through a vacuum pipeline via a vacuum pump; the refrigeration system and the vacuum system cool down and evacuate the drying chamber respectively, so as to form a freeze-drying space in the drying chamber during the sublimation drying stage; the heating system includes a heating partition and an electric heater at the bottom of the drying chamber, and the material in the drying chamber is heated by the heating system during the analytical drying stage; the control system includes a programmable controller, a frequency converter, a power supply, a control panel, a temperature sensor arranged in the drying chamber and a vacuum gauge arranged on the vacuum pipeline.

[0011] Moreover, the cold trap, condenser, cold air circulation pipeline, and the first and second circulation pipelines of the refrigerant liquid are all wrapped with thermal insulation materials to reduce the operating load of the refrigerator.

[0012] Moreover, an inlet of a cold air circulation pipeline is arranged at the center of the upper part of the drying chamber, and an outlet of the cold air circulation pipeline is arranged above the bottom end of the drying chamber.

[0013] Moreover, the pressure vessel, material container and drying chamber are all made of stainless steel.

[0014] Moreover, the bottoms of the cold trap and the condenser are both provided with drainage outlets.

[0015] Moreover, a filter screen is arranged inside the nozzle of the pressure atomizer.

[0016] Furthermore, the control system further comprises a temperature sensor installed on the cold trap and a temperature sensor installed inside the condenser.

[0017] Moreover, the heating baffle is made of stainless steel with good thermal conductivity, and an electric heater is arranged inside the heating baffle.

[0018] A spray freeze drying preparation method based on the spray freeze drying device of the solid malt extract powder with reduced dimethyl sulfide content, comprising the following steps:

[0019] 1) Precooling stage: open the valve of the first circulation pipeline of the refrigerant liquid of the refrigerator, close the other valves, circulate the refrigerant liquid in the first circulation pipeline of the refrigerant liquid that wraps the condenser, set the circulating refrigeration temperature to -80℃, start the refrigerator, and reduce the condenser temperature to -70℃~-75℃; open the valve of the cold air circulation pipeline connected to the drying chamber, connect the drying chamber with the condenser, fan, and separation dust collector; turn on the fan, set the wind speed to 5-6m / s, reduce the temperature of the drying chamber to -43~-46℃, and ensure that the drying chamber reaches the supercooling temperature that maintains the sublimation of the frozen material;

[0020] 2) Atomization stage: put the wort material into the pressure vessel and ensure that the pressure vessel is sealed; connect the pressure atomizer, air compressor and pressure vessel with the material delivery pipeline and pressure delivery pipeline; turn on the air compressor and adjust the pressure gauge until the pointer stabilizes to the 0.5MPa scale; fill the material container with about half of the volume of liquid nitrogen, place the pressure atomizer 5-7cm above the liquid nitrogen and start atomization; after atomization, turn off the air compressor and pull the pressure relief valve of the pressure vessel to release the pressure, the liquid nitrogen in the material container evaporates, and the wort material is frozen into wort particles of spherical ice crystals. At this time, all the dimethyl sulfide in the wort is converted into a solid phase;

[0021] 3) Sublimation drying stage: open the valve of the second circulation pipeline of the refrigerating machine, close the valve of the first circulation pipeline of the refrigerating machine, and circulate the refrigerating liquid in the second circulation pipeline of the refrigerating liquid wrapped in the cold trap, so that the temperature of the cold trap drops to -70°C to -73°C; turn off the fan, close the valve of the cold air circulation pipeline, and isolate the drying chamber from the condenser, the fan, and the separation dust collector; open the drying chamber, put the material container into the drying chamber, and close and seal the drying chamber; open the valve of the vacuum pipeline, connect the drying chamber with the vacuum pump and the cold trap, start the vacuum pump to vacuum the drying chamber, and the wort particles frozen into spherical ice crystals are sublimated and dried into dry materials, and the dimethyl sulfide attached to the surface of the wort particles is removed;

[0022] 4) Analysis and drying stage: Observe the control panel during the drying process. The control system displays the temperature and pressure changes in the drying chamber. When the pressure in the drying chamber drops to 20Pa, turn on the heating partition and set the heating temperature to 30-40°C. The bound water in the dried material and the residual dimethyl sulfide inside are removed. Continue to observe the changes in the vacuum degree during the analysis and drying process. The drying ends when the pressure reaches 4.5Pa.

[0023] 5) End of drying: When the pressure in the drying chamber reaches the required level, the drying is stopped. First, the heating partition is closed, the vacuum pump is closed, the refrigerator is closed, and the pressure relief valve 24 is opened to release the pressure. When the pressure in the drying chamber reaches normal pressure, the drying chamber is opened, and the prepared solid malt extract powder is taken out, and the drying is completed.

[0024] The advantages and beneficial effects of the present invention are:

[0025] 1. The solid malt extract spray freeze drying device and method of the present invention can reduce the content of dimethyl sulfide, directly atomize and freeze the material to be dried in the material container, and the material is always contained in the material container during the whole drying process, so as to avoid the material sticking to the wall and losing during the atomization process, thereby achieving a higher yield of the dried product, and the freezing medium uses liquid nitrogen at an extremely low temperature, which reduces the occurrence of agglomeration problems during atomization.

[0026] 2. The solid malt extract spray freeze drying device and method capable of reducing the dimethyl sulfide content of the present invention spray freezes the material into solid particles during the atomization stage, thereby increasing the surface area of ​​the material and accelerating the heat and mass transfer in the subsequent drying process. Compared with the traditional vacuum freeze drying, the drying time is significantly shortened and the energy consumption is saved.

[0027] 3. In the solid malt extract spray freeze-drying device and method for reducing the dimethyl sulfide content of the present invention, the first and second circulation pipelines of the refrigerant, the air inlet duct, and the air outlet duct are wrapped with insulation materials to keep the temperature stable during the refrigerant transportation and pre-cooling of the drying chamber, ensuring that frost will not appear on the inner wall of the drying chamber to affect the drying process.

[0028] 4. In the solid malt extract spray freeze drying device and method capable of reducing the content of dimethyl sulfide of the present invention, the vacuum pump is connected to the drying chamber via a cold trap, and the water vapor sublimated during the drying process can be collected in the cold trap, thereby increasing the service life of the vacuum pump.

[0029] 5. The solid malt extract spray freeze drying device and method capable of reducing the dimethyl sulfide content of the present invention can monitor the temperature of the cold trap, condenser, and drying chamber, as well as the pressure in the drying chamber in real time through a control panel; and can regulate the opening and closing of the fan, vacuum pump, and heating partition through the control panel.

[0030] 6. In the solid malt extract spray freeze-drying device and method capable of reducing the dimethyl sulfide content of the present invention, the pressure relief pipeline is connected to the drying chamber through a cold trap, and the pressure relief valve can not only relieve the pressure in the drying chamber, but also directly discharge the condensed water in the cold trap from the pressure relief valve to keep the cold trap clean.

[0031] 7. The solid malt extract spray freeze drying device and method of the present invention which can reduce the content of dimethyl sulfide, directly processes the wort into a granular solid malt extract powder product by adopting a spray freeze drying process, and does not require secondary crushing processing, so that solid malt extract powder with a round shape, uniform particle size and concentrated particle size can be directly obtained.

[0032] 8. The solid malt extract spray freeze drying device and method capable of reducing the content of dimethyl sulfide of the present invention, in the spray freezing stage, the wort material is atomized into a low-temperature liquid nitrogen medium, and the extremely low temperature increases the proportion of dissolved solids in the freezing matrix, and the soluble volatile compounds in the wort are retained to a greater extent than freeze drying; small ice crystals are formed by rapid freezing of the wort material when atomized in liquid nitrogen, and the small ice crystals are sublimated in the subsequent drying process, so that the surface of the prepared solid malt extract powder has a porous structure, and the solid malt extract powder absorbs water by capillaries when in contact with water and is quickly reduced to wort, so that the solid malt extract powder has excellent instantaneous solubility.

[0033] 9. The solid malt extract spray freeze drying device and method of the present invention can reduce the content of dimethyl sulfide. The vacuum environment during spray freeze drying inhibits the occurrence of oxidation reactions that are prone to produce impurities during the drying process, and retains the nutritional components of the wort material under a low temperature environment.

[0034] 10. The spray freeze drying device and method of the present invention can effectively reduce the content of dimethyl sulfide in wort. By analyzing the heat energy transfer from the heating partition during drying, the energy transition obtained in a short time increases the diffusion coefficient of gaseous dimethyl sulfide in the solid malt extract powder, so that the dimethyl sulfide gas that is not easily soluble in water is discharged from the solid malt extract powder.

[0035] 11. The spray freeze drying device and method for reducing dimethyl sulfide content of solid malt extract of the present invention. The bottom of the drying chamber of the spray freeze drying process of the present invention is equipped with a heating partition, which can directly conduct additional heat energy to the material in the drying analysis stage, and can bring appropriate energy transfer to the material above the heating partition in a short time, causing the convection movement of dimethyl sulfide inside the solid malt extract, so that dimethyl sulfide is discharged from the wrapped shell layer. In addition, the vacuum and low temperature environment of the spray freeze drying process inhibits the conversion of methyl methionine to dimethyl sulfide, and the heat energy conduction in the analysis stage can achieve the complete removal of dimethyl sulfide.

[0036] 12. The solid malt extract spray freeze-drying device and method for reducing the dimethyl sulfide content of the present invention adopts a high-power resistance heating method in the electric heater in the heating system. No matter what the ambient temperature is, the temperature can be raised to the set value in a short time, and the heat energy can be quickly transferred to the material through the alloy material heating baffle with excellent thermal conductivity.

[0037] 13. The solid malt extract spray freeze-drying device and method for reducing the dimethyl sulfide content of the present invention adopts the spray freeze-drying method to prepare solid malt extract powder. The obtained solid malt extract powder is a granular product with regular spherical shape and porous surface, which is completely different from the collapsed and agglomerated products of spray drying and the freeze-dried products with irregular flaky shapes obtained by secondary crushing after drying. The spray freeze-drying process of the present invention can directly prepare solid malt extract powder with good solubility and fluidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the structure of the atomization system of the solid malt extract spray freeze drying device of the present invention;

[0039] Figure 2 It is a schematic diagram of the structure of the refrigeration system, vacuum system, heating system and control system of the solid malt extract spray freeze drying device of the present invention;

[0040] Figure 3 This is a scanning electron microscope image of the prepared solid malt extract powder product;

[0041] Figure 4 This is a particle size distribution diagram of the prepared solid malt extract powder product;

[0042] Figure 5 The curve showing the change of dimethyl sulfide content in wort with drying time during the spray freeze drying process of the present invention;

[0043] Figure 6 The dimethyl sulfide content of the solid malt extract prepared by spray drying of the present invention is compared with that of solid malt extract sold on the market after re-dissolution of equal mass.

[0044] Description of Reference Numerals

[0045] 1-air compressor, 2-pressure relief valve, 3-pressure transmission pipeline, 4-pressure vessel, 5-wort material, 6-pressure gauge, 7-feeding pipeline, 8-material container, 9-pressure atomizer, 10-liquid nitrogen, 11-vacuum gauge, 12-drying chamber, 13-temperature sensor, 14-heating partition, 15-control panel, 16-first valve, 17-second valve, 18-condenser, 19-third valve, 20-separation dust collector, 21-fan, 22-drain port, 23-cold trap, 24-pressure relief valve, 25-fourth valve, 26-fifth valve, 27-sixth valve, 28-seventh valve, 29-refrigeration machine, 30-vacuum pump, 31-baffle wall. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0047] A solid malt extract spray freeze drying device capable of reducing the content of dimethyl sulfide comprises an atomization system, a refrigeration system, a vacuum freezing system, a heating system and a control system.

[0048] The atomization system includes an air compressor 1, a pressure vessel 4, a pressure atomizer 9, and a material container 8. The air compressor 1 is connected to the pressure vessel 4 through a pressure transmission pipeline, and the pressure atomizer 9 is connected to the pressure vessel 4 through a feed pipeline 7. The air compressor 1 compresses the air and provides pressure to the pressure vessel 4 through the pressure transmission pipeline 3. The wort material 5 contained in the pressure vessel 4 is pushed by the pressure and flows from the feed pipeline 7 to the pressure atomizer 9. After being pressurized, the wort material 5 is evenly atomized into the material container 8 in a fan shape. The outlet of the pressure atomizer 9 is located 5-7 cm above the material container 8, and liquid nitrogen 10 is contained in the material container 8. The pressure atomizer 9 atomizes the material in the pressure vessel 4 and sprays it into the material container 8 and freezes it in the material container 8. The inside of the nozzle of the pressure atomizer 9 can be fitted with a filter. The pressure vessel 4 is provided with a pressure relief valve 2 and a pressure gauge 6.

[0049] The refrigeration system includes a refrigerator 29, a condenser 18, a fan 21, and a drying chamber 12. The refrigerator 29 allows the low-temperature refrigerant in the body to circulate in the refrigerant pipeline. The first refrigerant circulation pipeline provides a wall-type cooling for the condenser 18. The fourth valve 25 and the seventh valve 25 are installed on the first refrigerant circulation pipeline, which are used to control the circulation of the refrigerant in the pipeline wrapped around the condenser 18. After the condenser 18 drops to a low temperature, the fan 21 can be turned on to circulate the dry cold air in the closed system composed of the condenser 18, the drying chamber 12, the separation dust collector 20, and the fan 21. The condenser 18 and the cold air circulation pipeline are wrapped with insulation materials to reduce the load of the refrigerator 29 during operation. The cold air circulation pipeline is equipped with a first valve 16 and a third valve 19, which are used to isolate the drying chamber 12 from the refrigeration system during drying. The drain port 22 can discharge the condensed water accumulated in the condenser 18 after drying to avoid contamination in the condenser 18.

[0050] The vacuum system includes a vacuum pump 30, a cold trap 23, and a drying chamber 12. The refrigerant circulates in the refrigerant pipeline. The second refrigerant circulation pipeline provides inter-wall cooling for the cold trap 23. The cold trap 23 is connected to the drying chamber 12 through the vacuum pipeline via the vacuum pump 30. The vacuum pump 30 is connected to the cold trap 23 and the drying chamber 12 through the vacuum pipeline by adjusting the second valve 17 to form a closed loop. After the vacuum pump 30 is turned on, the drying chamber 12 is quickly reduced to negative pressure. The cold trap 23 is used to capture the sublimated water vapor. After the drying is completed, the drying chamber 12 is depressurized by opening the valve 24, and the condensed water collected in the cold trap 23 can be discharged.

[0051] The refrigeration system and the vacuum system cool down and evacuate the drying chamber 12 respectively, so as to form a freeze-drying space in the drying chamber 12 during the sublimation drying stage.

[0052] The heating system includes a heating partition 14 and a built-in electric heater. The heating partition 14 is located at the bottom of the drying chamber 12. The temperature can be adjusted within 30°C to 40°C to provide the heat required for the drying and decomposition stage. The heating system heats the material in the drying chamber 12 during the decomposition and drying stage.

[0053] The cold trap 23 and the condenser 18 are arranged in a closed baffle, and the control system includes a programmable controller, a frequency converter, a power supply, a control panel 15 located above the baffle wall 31, a temperature sensor 13 arranged in the drying chamber 12, a temperature sensor arranged in the cold trap 23 and the condenser 18, and a vacuum gauge 11 arranged on the vacuum pipeline. A vacuum gauge 11 is installed on the vacuum pipeline from the cold trap 23 to the drying chamber 12, which is used to collect the vacuum degree signal in the drying chamber 12. Temperature sensors are installed in the drying chamber 12, the cold trap 23, and the condenser 18, which are used to collect real-time temperature, and the collected pressure and temperature are displayed on the control panel 15. The parameters of the spray freeze drying process can be set on the control panel 15 through PLC control, and the fan 21, the vacuum pump 30, and the heating partition 14 can all be turned on and off through the control panel 15.

[0054] A drying method using the solid malt extract spray freeze drying device capable of reducing the content of dimethyl sulfide, using wort as the experimental material, the drying comprises the following steps:

[0055] 1) Precooling stage: close the pressure relief valve 24, close the fifth valve 26 and the sixth valve 27, and isolate the drying chamber 1212 from the vacuum system; open the fourth valve 25 and the seventh valve 25, so that the refrigerant can circulate in the first circulation pipeline of the refrigerant liquid, set the refrigeration temperature of the refrigerator 29 to -80°C, and start the refrigerator 29 to make the temperature of the condenser 18 reach about -70°C to -75°C; open the first valve 16 and the third valve 19, so that the drying chamber 12 is connected to the condenser 18 through the cold air circulation pipeline; start the fan 21, set the wind speed to 5m / s, and make the temperature of the drying chamber 12 reach -43°C. Ensure that the drying chamber 12 reaches a supercooled temperature sufficient to maintain the sublimation of the frozen material to prevent the material from collapsing during the sublimation stage of drying.

[0056] 2) Atomization stage: After precooling, the wort material 5 is placed in the pressure container 4, the air compressor 1 is turned on to deliver pressure to the pressure container 4 through the pressure transmission pipeline 3, the pressure gauge 6 is adjusted so that the pointer scale reaches 0.5MPa, the nozzle of the pressure atomizer 9 is placed about 5cm above the liquid nitrogen 10, the pressure atomizer 9 is turned on to atomize the wort and fall into the liquid nitrogen in the material container 8, and the wort droplets are quickly frozen at an extremely low temperature of about -196°C in the liquid nitrogen 10. After the atomization is completed, the material container 8 is placed in the drying chamber 12. At this time, the material container 8 contains wort particles that are frozen in the shape of droplets. After the liquid nitrogen 10 in the material container 8 evaporates, wort particles frozen into spherical ice crystals are obtained, and at this time, the dimethyl sulfide in the wort is also completely converted into a solid phase.

[0057] 3) Sublimation drying stage: turn off the fan 21, close the first valve 16 and the third valve 19, and isolate the drying chamber 12 from the refrigeration system; open the fifth valve 26 and the sixth valve 27 to allow the refrigerant to circulate in the second circulation pipeline of the refrigerant liquid, so that the temperature of the cold trap 23 drops to -70°C; close the fourth valve 25 and the seventh valve 25 of the first circulation pipeline of the refrigerant liquid; open the second valve 17, connect the drying chamber 12 to the vacuum system, turn on the vacuum pump 30 to extract vacuum from the inside of the drying chamber 12, and the vacuum pump 30 has a vacuum rate of 1L / s; dimethyl sulfide attached to the surface of the frozen wort particles is removed during the sublimation drying stage.

[0058] At the beginning of the sublimation stage, the dimethyl sulfide in the frozen wort particles has officially begun to volatilize. Since the freezing medium in the atomization freezing stage of the spray freeze drying process is liquid nitrogen 10, the wort droplets are quickly frozen at an extremely low temperature, and ice crystals begin to nucleate and grow from the surface of the droplets and multiple disordered points inside, so that the dimethyl sulfide is randomly concentrated and dispersed on the surface and inside of the droplets. Therefore, the dimethyl sulfide located on the surface of the frozen droplets begins to volatilize together with free water in the initial sublimation stage of drying. However, the removal amount of dimethyl sulfide at this time is limited. As shown in formula (1), as the free water in the sample is removed, the solid concentration increases, and the diffusion coefficient of the volatile gas gradually decreases. Therefore, in the sublimation stage, dimethyl sulfide is only removed in the initial stage with a high free water content. When only bound water remains in the material in the later stage of drying, the decline rate of dimethyl sulfide will gradually stabilize, and it is more difficult to discharge dimethyl sulfide enclosed in the shell.

[0059]

[0060] In the formula: D 0 = Initial diffusion coefficient

[0061] E = Energy required to overcome the activation barrier and create molar vacancies (provided by heated baffle 14)

[0062] R, T = gas law constant

[0063] 4) Analysis and drying stage: During the drying process, the pressure change in the drying chamber 12 on the control panel 15 is observed. When the pressure drops to 20 Pa, the heating partition 14 is opened and the heating temperature is set to 35° C., so that the drying enters the analysis stage of removing bound water. The bound water in the dried material and the residual dimethyl sulfide inside are removed; the pressure change on the control panel 15 is continued to be observed. When the pressure drops below 4.5 Pa, the drying is stopped.

[0064] In the spray freeze drying process of the present invention, opening the heating baffle 14 in the analytical drying stage is an important step in removing dimethyl sulfide. As mentioned above, in the late sublimation stage, the remaining dimethyl sulfide is difficult to remove due to the decrease in the diffusion coefficient. The benefit effect of opening the heating baffle 14 for the removal of dimethyl sulfide is shown in formula (2). Previously, as the solid concentration in the frozen wort increased, the energy required for the volatile compound molecules to move from one free space to another space increased, slowing down the diffusion. The opening of the heating baffle 14 quickly transfers the heat energy of the material located above in a low-temperature environment, providing dimethyl sulfide with additional energy for breaking the barrier of smooth molecular motion, thereby increasing the diffusion rate of dimethyl sulfide and inducing the dimethyl sulfide wrapped inside to produce convection motion and be smoothly discharged from the malt extract.

[0065]

[0066] In the formula: D 0 = Initial diffusion coefficient

[0067] E = Energy required to overcome the activation barrier and create molar vacancies (provided by heated baffle 14)

[0068] R, T = gas law constant

[0069] 5) End of drying: After the pressure in the drying chamber 12 reaches the required pressure, the drying experiment is stopped. First, the heating partition 14 is closed, the vacuum pump 30 is closed, the refrigerator 29 is closed, and the pressure relief valve 24 is slowly opened to release the pressure in the drying chamber 12. When the pressure in the drying chamber 12 reaches normal pressure, the drying chamber 12 is opened, the solid malt extract powder sample is taken out, and the drain port 22 is opened, and the drying is completed.

[0070] The spray freeze drying device of the present invention uses a separate material container 8 to hold frozen wort particles in the atomization stage. Since wort is a highly viscous material rich in sugar, the risk of wall adhesion during the atomization process is reduced, thereby improving the product yield; and the atomization process increases the specific surface area of ​​the wort droplets, accelerates the mass transfer rate in the subsequent drying process, and shortens the drying time compared to traditional freeze drying, thereby saving more production energy consumption; in addition, the drying process of the present invention is carried out under negative pressure, and the heating temperature in the analysis stage can be freely controlled.

[0071] The dimethyl sulfide content test method of the present invention adopts gas chromatograph to perform internal standard method determination, with dimethyl sulfide as standard and methyl ethyl sulfide as internal standard. After the material to be tested is placed in a headspace bottle for pretreatment, the headspace is extracted and sampled for dimethyl sulfide content detection. To ensure the accuracy of the results, each test is repeated three times and the average value is calculated.

[0072] The above operation is a complete process for preparing solid malt extract with dimethyl sulfide removed in the present invention. However, in order to demonstrate the change in the content of dimethyl sulfide during the spray freeze drying process, the following experiment is used: the above drying process is repeated multiple times, and the difference each time is that the drying is ended at different time periods after the vacuum is drawn in step 4, and the dimethyl sulfide content of the material in the material container 8 is taken out; in addition, a group of control spray freeze drying processes for preparing solid malt extract are carried out without opening the heating partition 14, and the drying is also ended at different drying times after the vacuum is drawn. Finally, the dimethyl sulfide content measured at different time periods during the spray freeze drying process in the two groups of experiments is plotted as Figure 5 The line chart shown.

[0073] The moisture content of the solid malt extract powder prepared by the present invention is about 4.2%, which is lower than 5% and meets the moisture content standard of the powder. Figure 3 The particle size distribution diagram of the solid malt extract powder prepared by the present invention is shown in Figure 4 As shown; Figure 5 The curve of dimethyl sulfide content in wort during the spray freeze drying process of the present invention as a function of drying time is shown in the figure. The dimethyl sulfide content in the solid malt extract powder prepared by the present invention is compared with that in the solid malt extract powder currently sold on the market. Figure 6 shown.

[0074] like Figure 3 As shown, the microscopic morphology of the solid malt extract powder prepared by the present invention presents a regular round appearance, and each particle has a uniform shape, which is due to the rapid freezing of the droplets in the liquid nitrogen 10 during the atomization stage, and the smooth sublimation process during the drying stage maintains the shape of the material when it is frozen. This feature makes the solid malt extract powder have good fluidity. The image shows that the surface of the solid malt extract powder has a pore structure distribution, which is due to the traces left by the sublimation of small ice crystals generated on the surface when the droplets are rapidly frozen. The pore structure connected to the inside will bring excellent solubility to the solid malt extract powder.

[0075] like Figure 4 As shown, the particle size differential distribution of the solid malt extract powder of the present invention presents a narrow single peak that is unique to spray freeze-dried products, indicating that the powder particle size distribution is uniform, and the overall particle size is concentrated around 100 μm. This is due to the atomization and freezing stage of the present invention, which uniformly atomizes the wort into small-sized droplets, which then come into contact with low-temperature liquid nitrogen 10 to produce rapid freezing, maintaining the droplet shape during atomization, and in the subsequent low-stress water sublimation process, the product is kept in the frozen state, and granular solid malt extract powder is directly obtained after drying, which is different from traditional freeze drying that requires secondary crushing, and is different from commercially available spray-dried products that are prone to collapse, agglomeration and the like. The solid malt extract powder of the present invention has a small and concentrated powder particle size, which provides convenience for powder packaging and pouring.

[0076] like Figure 5 As shown, the change of dimethyl sulfide content during the spray freeze drying process of the present invention is shown in detail. In addition to the case where the heating baffle 14 is turned on in this embodiment, the change of dimethyl sulfide under the spray freeze drying process conditions where the heating baffle 14 is not turned on and only the sublimation stage exists is also shown. It can be seen from the curve when the heating baffle 14 is not turned on that the dimethyl sulfide content decreases from 720μg / L to 300μg / L within 100 minutes in the early stage of the sublimation stage. The high rate of decrease is due to the low temperature and vacuum environment of the spray freeze drying process, which inhibits the thermal cracking of methyl methionine to generate dimethyl sulfide, so that the dimethyl sulfide in the frozen wort reaches a unidirectional sublimation process. Starting from about 120 minutes in the late stage of sublimation drying, the rate of decrease of dimethyl sulfide gradually decreases, and finally the dimethyl sulfide content is maintained at 60μg / L and tends to be stable. The stable molecular motion at low temperature is not enough to support the continued mass transfer of the remaining dimethyl sulfide. Another dimethyl sulfide change curve of the drying process with the heating baffle 14 turned on shows that after the heating baffle 14 is turned on for 120 minutes, the dimethyl sulfide content decreases from 320 μg / L to 20 μg / L in only 50 minutes, achieving a sharp decline. The heat energy transfer of the heating baffle 14 to the material in the present invention is fast and sudden, so that the dimethyl sulfide obtains additional energy, breaking the original stable mass transfer process. The dimethyl sulfide content has been reduced to 0 μg / L in the 260-minute period, so that it is completely removed from the solid malt extract in the analysis stage.

[0077] like Figure 6 As shown, the dimethyl sulfide content of the solid malt extract prepared by spray drying of the present invention is compared with that of the solid malt extract sold on the market after reconstitution of equal mass. It is observed that about 86 μg / L of dimethyl sulfide still remains in the commercially available solid malt extract. The dimethyl sulfide content of the solid malt extract of the present invention after reconstitution of equal mass is 0 μg / L.

[0078] Since the current commercially available solid malt extract is prepared by a spray drying process, due to the film-forming mechanism of the droplets during the spray drying process, dimethyl sulfide in the wort is not easy to be discharged, and due to the continuous cracking and generation of dimethyl sulfide under high temperature and aerobic environment, the commercially available solid malt extract usually has a relatively large residual dimethyl sulfide content. However, the spray freeze drying process in the present invention is carried out in a low-temperature vacuum environment, which effectively inhibits the regeneration of dimethyl sulfide by methylmethionine, and a large amount of dimethyl sulfide is removed in the sublimation stage. Then, by controlling the opening of the heating partition 14, the molecules are given enough energy to break the obstacles of position change, and dimethyl sulfide is more thoroughly eliminated from the solid malt extract, and finally a solid malt extract with a lower content of dimethyl sulfide than the commercially available solid malt extract powder is prepared. The lower dimethyl sulfide content reduces the pungent rotten corn smell of the wort after the solid malt extract powder is restored, so that the wort smell highlights the original malt aroma characteristics.

[0079] Although the embodiments of the present invention and the drawings are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims, and therefore the scope of the present invention is not limited to the contents disclosed in the embodiments and the drawings. Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims, and therefore the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A spray-freezing drying preparation method of a solid malt extract spray-freezing drying device capable of reducing the content of dimethyl sulfide, which comprises the following steps: 1) Pre-cooling stage: Open the valve of the first refrigerant circulation pipeline of the refrigerator (29), close the remaining valves, the refrigerant circulates in the pipeline of the first refrigerant circulation pipeline wrapping the condenser (18), set the circulating refrigeration temperature to -80 °C, turn on the refrigerator (29) to reduce the temperature of the condenser (18) to -70 °C to -75 °C; Open the valve of the cold air circulation pipeline connected to the drying chamber (12), connect the drying chamber (12) with the condenser (18), the fan (21), and the separation dust collector (20); Turn on the fan (21), set the wind speed to 5 - 6 m / s, reduce the temperature of the drying chamber (12) to -43 °C to -46 °C, and ensure that the supercooling temperature for maintaining the sublimation of the frozen material is reached inside the drying chamber (12); 2) Atomization stage: Load the wort material (5) into the pressure vessel (4) and ensure the pressure vessel (4) is sealed; Connect the pressure atomizer (9), the air compressor (1) with the pressure vessel (4) through the feeding pipeline (7) and the pressure relief valve (2); Turn on the air compressor (1) and adjust the pressure gauge (6) until the pointer stabilizes at the 0.5 MPa scale; Load about half of the volume of liquid nitrogen (10) into the material container (8), place the pressure atomizer (9) 5 - 7 cm above the liquid nitrogen (10) to start atomization; After atomization, turn off the air compressor (1), and pull the pressure relief valve (2) of the pressure vessel (4) to relieve pressure; The liquid nitrogen (10) in the material container (8) volatilizes, and the wort material (5) freezes into wort particles in the shape of spherical ice crystals. At this time, all the dimethyl sulfide in the wort is converted into the solid phase; 3) Sublimation drying stage: Open the valve of the second refrigerant circulation pipeline of the refrigerator (29), close the valve of the first refrigerant circulation pipeline of the refrigerator (29), the refrigerant circulates in the pipeline of the second refrigerant circulation pipeline wrapping the cold trap (23), and reduce the temperature of the cold trap (23) to -70 °C to -73 °C; Turn off the fan (21), close the valve of the cold air circulation pipeline, and isolate the drying chamber (12) from the condenser (18), the fan (21), and the separation dust collector (20); Open the drying chamber (12), put the material container (8) into the drying chamber (12), close and seal the drying chamber (12); Open the valve of the vacuum pipeline, connect the drying chamber (12) with the vacuum pump (30) and the cold trap (23), turn on the vacuum pump (30) to extract vacuum from the inside of the drying chamber (12), and the wort particles frozen into spherical ice crystals are sublimated and dried into dry materials, and the dimethyl sulfide attached to the surface of the wort particles is removed; 4) Desorption drying stage: Observe the control panel (15) during the drying process, the control system displays the temperature and pressure changes inside the drying chamber (12), turn on the heating partition (14) when the pressure inside the drying chamber (12) drops to 20 Pa, and set the heating temperature to 30 - 40 °C; The bound water and the residual dimethyl sulfide inside the dry material are removed; Continue to observe the change of the vacuum degree during the desorption drying process, and the drying ends when the pressure reaches 4.5 Pa; 5) End of drying: Stop drying after the pressure in the drying chamber (12) reaches the required value. First, close the heating partition (14), the vacuum pump (30), and the refrigerator (29), and open the pressure relief valve (2) to relieve the pressure. When the pressure in the drying chamber (12) reaches atmospheric pressure, open the drying chamber (12) and take out the prepared solid malt extract powder, and the drying is completed. The solid malt extract spray freeze-drying device capable of reducing the dimethyl sulfide content includes an atomization system, a refrigeration system, a vacuum freezing system, a heating system, and a control system. The atomization system includes an air compressor (1), a pressure atomizer (9), a pressure vessel (4), and a material container (8). The air compressor (1) is connected to the pressure vessel (4) through a pressure transmission pipeline. The pressure atomizer (9) is connected to the pressure vessel (4) through a material transmission pipeline (7). The outlet of the pressure atomizer (9) is located above the material container (8). Liquid nitrogen (10) is contained in the material container (8). The pressure atomizer (9) atomizes and sprays the material in the pressure vessel (4) into the material container (8) and freezes it in the material container (8). The refrigeration system includes a refrigerator (29), a condenser (18), a fan (21), and a separation dust collector (20). The refrigerant of the refrigerator (29) circulates back to the refrigerator (29) through the first refrigerant circulation pipeline wound around the condenser (18). The condenser (18) and the fan (21) are connected to the drying chamber (12) through a cold air circulation pipeline. The vacuum system includes a vacuum pump (30), a cold trap (23), and a drying chamber (12). The refrigerant of the refrigerator (29) circulates back to the refrigerator (29) through the second refrigerant circulation pipeline wound around the cold trap (23). The cold trap (23) is connected to the drying chamber (12) through a vacuum pipeline by the vacuum pump (30). The refrigeration system and the vacuum system respectively cool down and evacuate the drying chamber (12), so as to form a freeze-drying space in the drying chamber (12) during the sublimation drying stage. The heating system includes a heating partition (14) at the bottom of the drying chamber (12) and an electric heater, and heats the material in the drying chamber (12) through the heating system during the analytical drying stage. The control system includes a programmable controller, a frequency converter, a power supply, a control panel (15), a temperature sensor (13) arranged in the drying chamber (12), and a vacuum gauge tube (11) arranged on the vacuum pipeline.

2. The spray freeze-drying preparation method of the solid malt extract spray freeze-drying device capable of reducing the dimethyl sulfide content according to claim 1, characterized in that: The cold trap (23), the condenser (18), the cold air circulation pipeline, and the first and second refrigerant circulation pipelines are all wrapped with heat-insulating materials on the outside to reduce the operating load of the refrigerator (29).

3. The spray freeze-drying preparation method of the solid malt extract spray freeze-drying device capable of reducing the dimethyl sulfide content according to claim 1, characterized in that: An inlet of the cold air circulation pipeline is provided at the center above the drying chamber (12), and an outlet of the cold air circulation pipeline is provided above the bottom end of the drying chamber (12).

4. The spray-freezing drying preparation method of the solid malt extract spray-freezing drying device capable of reducing the dimethyl sulfide content according to claim 1, characterized in that: the pressure vessel (4), the material container (8), and the drying chamber (12) are all made of stainless steel.

5. The spray-freezing drying preparation method of the solid malt extract spray-freezing drying device capable of reducing the dimethyl sulfide content according to claim 1, characterized in that: drain ports (22) are provided at the bottoms of the cold trap (23) and the condenser (18).

6. The spray-freezing drying preparation method of the solid malt extract spray-freezing drying device capable of reducing the dimethyl sulfide content according to claim 1, characterized in that: a filter screen is installed inside the nozzle of the pressure atomizer (9).

7. The spray-freezing drying preparation method of the solid malt extract spray-freezing drying device capable of reducing the dimethyl sulfide content according to claim 1, characterized in that: the control system further includes a temperature sensor installed in the cold trap (23) and a temperature sensor installed inside the condenser (18).

8. The spray-freezing drying preparation method of the solid malt extract spray-freezing drying device capable of reducing the dimethyl sulfide content according to claim 1, characterized in that: the heating partition (14) is made of stainless steel with good heat conduction performance, and an electric heater is arranged inside the heating partition (14).

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