JP5415968B2 - Method and apparatus for drying food material vulnerable to heat denaturation - Google Patents

Description

  The present invention relates to a method for drying a food material vulnerable to heat denaturation and a drying apparatus that can dry the food material vulnerable to heat denaturation in a good state and at low cost while maintaining the state of color, shape, nutrients and the like.

  Conventionally, low-temperature hot-air drying methods and vacuum freeze-drying methods are known for drying food materials that are vulnerable to heat denaturation, such as vegetables and fruits. In the low-temperature hot-air drying method, the evaporation speed is slow because the drying is performed at a temperature below the boiling point of water, and it takes a long time to dry, and the food is oxidized and discolored or denatured. In addition, there is a problem that low temperature air cannot steam or sterilize food. On the other hand, in the vacuum freeze-drying method, since a freezing step is added, there is a problem that the drying time becomes long, the equipment becomes complicated and expensive.

  In recent years, a dry sterilization apparatus (see Patent Document 1) using a reduced pressure superheated steam, a reduced pressure low temperature drying apparatus (see Patent Document 2), and the like have been proposed. However, the device described in Patent Document 1 is a device that directly heats the material with hot air by convection heat transfer, and since the amount of gas present in the drying chamber is low under reduced pressure, the drying efficiency is poor, and heating and drying are difficult. It takes a long time and is not suitable for practical use.

  On the other hand, the device described in Patent Document 2 is a device of a radiation maturation method in which a heat pipe is provided at the bottom of each shelf and heated by radiant heat, and a heat pipe is required for each shelf, and the device must be enlarged. There is a problem that it cannot be steamed or sterilized as in the low temperature hot air drying method.

  In order to efficiently dry foods that are vulnerable to heat denaturation without being discolored, deformed, or altered, it is an important issue how to efficiently transfer heat to the food material during drying under reduced pressure. In addition, there is a demand for a drying apparatus that has both a low-temperature steaming function for imparting an umami component and a sterilizing function for improving storage stability in one drying apparatus.

JP 2005-287373 A JP 2007-85600 A

  Therefore, an object of the present invention is to dry a food material vulnerable to heat denaturation that can be efficiently dried without denaturing the food material vulnerable to heat denaturation and obtain a desired moisture content. And it is providing the simple drying apparatus suitable for the drying method.

  In order to achieve the above object, the method for drying a food material vulnerable to heat denaturation according to the first aspect of the present invention provides a lower pressure and a lower temperature limit when drying a food material vulnerable to heat denaturation under reduced pressure. In addition to setting the upper limit pressure and the upper limit temperature at that time, lowering the pressure to the lower limit pressure to evaporate the water content of the food material and reaching the lower limit temperature which is the saturation temperature at the lower limit pressure, then 100 A low-temperature water vapor of not more than 0 ° C. is injected to heat the food material from the lower limit temperature to the upper limit temperature, reach the upper limit pressure, and this operation is repeated to reduce the moisture content of the food material.

According to a second aspect of the present invention, there is provided a method for drying a food material that is vulnerable to heat denaturation. In the first aspect of the invention, the low-temperature steam is low-temperature superheated steam.
The method for drying a food material vulnerable to heat denaturation according to claim 3 is the invention according to claim 1 or 2, wherein the lower limit pressure and the upper limit pressure are in the range of 3 to 92 kPa in absolute pressure. It is characterized by being set.

  The drying device for food materials vulnerable to heat denaturation according to the invention of claim 4 is a drying device used in the method for drying food materials vulnerable to heat denaturation according to any one of claims 1 to 3. A drying chamber for containing and drying food materials that are vulnerable to thermal denaturation, and a lower limit that is a saturation temperature at the lower limit pressure by evaporating the moisture of the food material by lowering the pressure in the drying chamber to a lower limit pressure A pressure reducing unit for reaching the temperature, and a low temperature steam generating unit for injecting the low temperature steam into the drying chamber to heat the food material from the lower limit temperature to the upper limit temperature to reach the upper limit pressure. It is characterized by.

  According to a fifth aspect of the present invention, there is provided a drying apparatus for food materials that is vulnerable to thermal denaturation. In the invention according to the fourth aspect, the low-temperature steam generation unit is configured to supply electricity for heating low-temperature steam to generate low-temperature superheated steam. A heater is provided.

  The drying apparatus for food materials vulnerable to thermal denaturation of the invention described in claim 6 is the invention according to claim 4 or 5, wherein the drying cabinet is provided with a cooler for cooling water vapor. And

According to the present invention, the following effects can be exhibited.
In the method for drying a food material according to the present invention, when a food material that is susceptible to thermal denaturation is dried under reduced pressure, a lower limit pressure and a lower limit temperature are set, and an upper limit pressure and an upper limit temperature are set. And after lowering the pressure to the lower limit pressure to evaporate the moisture in the food material and reaching the lower limit temperature which is the saturation temperature at the lower limit pressure, low temperature steam at 100 ° C. or less is injected to make the food material the lower limit Heat from the temperature to the upper limit temperature, reach the upper limit pressure, and repeat this operation to reduce the moisture content of the food material.

  In this way, since the heating operation is performed with low-temperature steam after the pressure is reduced by the decompression operation, the food material can be dried at a low temperature, and at the same time, the heat can be efficiently transferred to the food material. The self-evaporation is promoted to improve the drying speed.

  Therefore, according to the present invention, it is possible to efficiently dry the food material that is vulnerable to heat denaturation, and to obtain a desired moisture content.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic explanatory drawing which shows the drying apparatus of the food material weak to heat denaturation in embodiment of this invention. The plane sectional view showing the outline of a drying warehouse. The graph which shows the relationship between time in a drying process, absolute pressure, and temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described in detail with reference to FIGS.
First, a food material drying apparatus that is vulnerable to heat denaturation will be described. As shown in FIG. 1, a food material drying apparatus 10 that is vulnerable to heat denaturation includes a drying chamber 11 for storing and drying food materials that are vulnerable to thermal denaturation, and a decompression pressure for reducing the pressure inside the drying chamber 11. A unit 20 and a low-temperature steam generation unit 30 for heating the inside of the drying cabinet 11 are provided. Examples of food materials that are vulnerable to heat denaturation include vegetables such as carrots, sweet potatoes, and radishes, and fruits such as strawberries, cui, pineapple, blueberries, and prunes.

  The drying cabinet 11 is a square box-type airtight container having a heat insulating structure, and a door 12 that is open to the left and right is attached to one side wall thereof. As shown in FIG. 2, trays 13 indicated by two-dot chain lines are arranged at predetermined intervals in the front and rear (upper and lower sides in FIG. 2) in the drying chamber 11, and are vulnerable to heat denaturation (not shown) on these trays 13. Food material is placed. Axial fans 14 capable of rotating in the forward and reverse directions are supported at four locations on the side wall facing the open / close door 12 in the drying chamber 11, and the gas (air) in the drying chamber 11 is indicated by a one-dot chain line in FIG. It is made to turn in the reverse direction shown by a direction and a dashed-two dotted line.

  In order to further increase the drying speed of the food material, a heater (heater using steam) 15 and a cooler (cooler using cooling water) 16 are used. As shown in FIG. 1, the heater 15 is disposed so as to face the axial fan 14, and steam is sent from a boiler 31 described later via a heating valve 36. This heater 15 is used to heat the gas in the drying chamber 11, and in particular when the food material is dried to a low moisture content, the steam valve 35, which will be described later, is closed at the time of finish drying, and reduced-pressure hot air drying is performed only by the heater 15. Do. Further, when the cooler 16 is used during the evaporation period of the drying process, the evaporation rate can be further increased.

  The heater 15 is arranged at a position opposite to the axial fan 14, so that the gas in the drying chamber 11 is circulated by the wind sent from the axial fan 14, and the food material is indirectly heated with water vapor. Yes. As shown in FIG. 2, the cooler 16 is arrange | positioned in the front-back center position in the drying chamber 11 so that it may extend in the left-right direction in a pair of front-and-rear partition frames 17. The left and right ends of the partition frame 17 are open, and a part of the gas flows from the opening / closing door 12 side toward the axial fan 14 as shown by the broken lines in FIG. A damper (not shown) may be provided at the opening of the end of the partition frame 17 on the opening / closing door 12 side to adjust the air volume of the inflowing gas. The water vapor in the drying chamber 11 is cooled by the cooling water of the cooler 16.

  Next, the decompression unit 20 will be described. As shown in FIG. 1, one end of a condenser 22 is connected to the vacuum pump 21, and the other end is connected to the drying chamber 11 via a pressure reducing valve 23. A connecting pipe 25 is connected to the lower part of the condenser 22 and is connected to the cooler 16 via a cooling valve 24. The decompression unit 20 can reduce the pressure in the drying chamber 11 to a set lower limit pressure, and can reach an upper limit pressure.

  Next, the low temperature steam generation unit 30 will be described. As shown in FIG. 1, a separator 31 that removes impurities and water droplets contained in the high-pressure steam is connected to a boiler 31 that generates high-pressure steam by a connection pipe. A pressure reducing valve body 33 for reducing the pressure is connected. The decompression valve body 33 generates low-temperature steam decompressed from high-pressure steam. The pressure reducing valve body 33 is connected to an electric heater 34 that further heats the low-temperature steam to produce low-temperature superheated steam, and the low-temperature superheated steam generated by the electric heater 34 is introduced into the drying chamber 11 through the steam valve 35. It is like that. When the moisture content of the food material can be 50% or more, low-temperature steam is used, and when the moisture content is desired to be 20% or less, low-temperature superheated steam is used. When low temperature steam is used, the electric heater 34 is turned off.

Next, a method for drying food materials that are vulnerable to heat denaturation will be described.
First, foods such as vegetables and fruits are arranged in a tray 13 in the drying cabinet 11 and stored in the drying cabinet 11 as food materials that are subject to thermal denaturation, which is an object to be dried. Subsequently, the opening / closing door 12 is closed and the axial fan 14 and the vacuum pump 21 are driven. The axial fan 14 is preset by a timer so that the forward rotation and the reverse rotation change in about 5 minutes.

  And a steaming process and a sterilization process are implemented. In this steaming and sterilization process, the temperature in the drying chamber 11 is set to 50 to 95 ° C., the absolute pressure is set to an arbitrary value of 96.3 to 31.3 kPa (gauge pressure −5 to −70 kPa), and the steam valve 35 and the pressure reducing valve 23 are opened, and after reaching the set temperature and absolute pressure, a steaming process and a sterilization process are performed by a timer for 10 to 60 minutes. The set value is adjusted by automatically opening and closing the valve with a temperature controller and a pressure controller (not shown).

  Next, in the drying step, drying is performed while repeating pressure fluctuations between the lower limit pressure and the upper limit pressure that match the boiling points of the lower limit temperature and the upper limit temperature. The lower limit pressure and the upper limit pressure are set within the range of 3 to 92 kPa as absolute pressure, and the lower limit temperature and the upper limit temperature are set within the range of 30 to 97 ° C.

  For example, as shown in FIG. 3, the upper limit temperature T1 is set to 60 ° C. and the upper limit absolute pressure P1 is set to 21.3 kPa (gauge pressure −80 kPa) on the high temperature side, and the lower limit temperature T2 is set to 40 ° C. and the lower limit absolute pressure on the low temperature side. P2 is set to 6.3 kPa (gauge pressure -95 kPa). And after completion | finish of a steaming process and a sterilization process, the pressure-reduction valve 23 is opened, the steam valve 35 is closed, and the inside of the drying chamber 11 is pressure-reduced to the minimum absolute pressure P2 set by the low temperature side. The pressure in the drying chamber 11 decreases from the normal pressure (101.3 kPa) to the lower limit absolute pressure P2 (6.3 kPa), and the moisture evaporates until the food material reaches the saturation temperature due to the reduced pressure, and the lower limit temperature T2 (40 ° C. ) And hold at that temperature for t2 hours (evaporation period).

  When the temperature of the food material reaches 40 ° C., the pressure reducing valve 23 is closed, the steam valve 35 is opened, and the low-temperature superheated steam is introduced into the drying chamber 11. Then, the food material in the drying chamber 11 is heated by the low-temperature superheated steam and reaches 21.3 kPa which is the upper limit absolute pressure P1 set on the high temperature side. The inside of the drying chamber 11 is heated until reaching the saturation temperature of 60 ° C. at the upper limit absolute pressure P1, and held at that temperature for t1 time (heating period).

  After the temperature of the food material reaches 60 ° C., the decompression valve 23 is opened, the steam valve 35 is closed, and the inside of the drying chamber 11 is decompressed to 6.3 kPa which is the lower limit absolute pressure P2 set on the low temperature side. By repeating the operations on the low temperature side (evaporation period) and the high temperature side (heating period) several tens of times, moisture in the food material evaporates and the food material is dried to a predetermined moisture content. That is, it takes a long time to convectionly heat the food material with air under reduced pressure, but the food material can be heated in a short time by employing heat transfer heating with water vapor.

  In addition, after completion | finish of a steaming process or a drying process, quick cooling of food material may be performed in order to prevent fermentation or growth of fungi. In order to perform rapid cooling, vacuum cooling is performed using the vacuum pump 21 and the cooler 16. That is, the decompression valve 23 is opened, the inside of the drying chamber 11 is decompressed to an absolute pressure of 3.3 kPa (gauge pressure -98 kPa), and the cooling valve 24 is opened, and the water vapor in the drying chamber 11 is condensed by passing cooling water through the cooler 16. Thus, rapid cooling can be performed.

The effects exhibited by the above embodiment will be described together below.
(1) In the method for drying a food material according to the present embodiment, when drying a food material vulnerable to heat denaturation under reduced pressure, a lower limit absolute pressure P2 and a lower limit temperature T2 are set, and an upper limit absolute pressure P1 and The upper limit temperature T1 is set. And after lowering the pressure to the lower limit absolute pressure P2 to evaporate the water content of the food material and reaching the lower limit temperature which is the saturation temperature at the lower limit absolute pressure P2, low temperature steam is injected to make the food material the upper limit temperature T1. Until the upper limit absolute pressure P1 is reached, and this operation is repeated to reduce the moisture content of the food material.

  In this way, since the heating operation is performed with low-temperature steam after the pressure is reduced by the decompression operation, the food material can be dried at a low temperature, and at the same time, the heat can be efficiently transferred to the food material. The self-evaporation is promoted to improve the drying speed.

  Therefore, according to this embodiment, it is possible to efficiently dry the food material that is vulnerable to heat denaturation, and to obtain a desired moisture content. The food material can be dried in a good state and at a low cost while maintaining the color, shape, nutrients, and the like of the food material.

(2) By using low-temperature superheated steam as the low-temperature steam, the moisture content of the food material after drying can be easily reduced to, for example, 20% or less.
(3) By setting the lower limit pressure and the upper limit pressure in the range of 3 to 92 kPa as absolute pressure, the pressure fluctuation can be sufficiently performed, and the drying efficiency of food materials vulnerable to heat denaturation can be improved. it can. Furthermore, by setting a large pressure difference between the lower limit pressure and the upper limit pressure, the moisture content of the food material after drying can be further reduced.

(4) By setting the lower limit temperature and the upper limit temperature within the range of 40 to 70 ° C., the food material can be dried without being thermally denatured.
(5) As a food material drying apparatus 10 that is vulnerable to heat denaturation, a drying cabinet 11 for storing and drying food materials, a decompression unit 20 for reducing the pressure in the drying cabinet 11 to a predetermined pressure, and drying By configuring the storage 11 with the low-temperature steam generation unit 30 for heating the interior to a predetermined temperature, the configuration of the apparatus can be simplified. In addition, in addition to the drying process, the steaming process and the sterilization process can be performed simultaneously in one drying chamber 11, and efficient and economical drying can be performed.

(6) By providing the electric heater 34 in the water vapor generating unit, the low temperature water vapor can be easily generated by heating the low temperature water vapor with the electric heater 34.
(7) By providing the cooler 16 in the drying chamber 11 and circulating the gas in the drying chamber 11 by the axial fan 14, the water vapor in the drying chamber 11 can be efficiently cooled, and the conventional drying chamber 11 The condenser for the cooler provided outside the battery can be omitted, and the apparatus can be simplified.

Hereinafter, the embodiment will be described more specifically with reference to examples.
Example 1
The carrot as a food material vulnerable to heat denaturation was cut into pieces, and 2 kg of carrot was placed in one tray 13 (area 0.4 m ² ) to sterilize and dry.

  First, in the sterilization process, the temperature in the drying chamber 11 was set to 65 ° C. and the absolute pressure was 41.3 kPa (gauge pressure—60 kPa), and sterilization was performed for 30 minutes after the temperature was raised. In the drying step, the upper limit temperature T1 on the high temperature side is set to 60 ° C., the upper limit absolute pressure P1 is set to 21.3 kPa (gauge pressure −80 kPa), the lower limit temperature T2 on the low temperature side is set to 40 ° C., and the lower limit absolute pressure P2 is set to 6.3 kPa. It set to (gauge pressure -95kPa), and it dried with the low temperature superheated steam for 5 hours. Thereafter, using a heater 15, vacuum hot air drying was performed for 4 hours at a temperature of 60 ° C. and an absolute pressure of 41.3 kPa (gauge pressure—60 kPa). The dried carrot had a water content of 10% or less, and the color remained beautiful.

On the other hand, when the normal pressure hot air drying operation was performed at a temperature of 60 ° C., the drying time was 18 hours and the color was slightly faded.
(Example 2)
Steaming, drying and cooling were carried out to make the sweet potato into a dried potato.

  First, in the steaming step, 10 kg of the sweet potato was left in a log and placed in one tray 13 and steamed with low temperature steam at a temperature of 90 ° C. and an absolute pressure of 81.3 (gauge pressure−20 kPa) for 1 hour. After completion of the steaming process, the product was taken out from the drying chamber 11, and the log firewood was cut into round slices and placed 2 kg in one tray 13.

  In the drying step, the upper limit temperature T1 on the high temperature side is 70 ° C., the upper limit absolute pressure P1 is 41.3 kPa (gauge pressure −60 kPa), the lower limit temperature T2 on the low temperature side is 40 ° C., and the lower limit absolute pressure P2 is 11.3 kPa (gauge). The pressure was set to -90 kPa) and drying was performed for 3 hours. After completion of drying, cooling water was passed through the cooler 16 to make the inside of the drying chamber 11 at 3.3 kPa (gauge pressure -98 kPa) in absolute pressure, and vacuum cooling was performed until the temperature of the soot reached 30 ° C. The dried persimmons after cooling had a moisture content of 50% and had a beautiful amber color. They were softer and sweeter than conventional sun-dried persimmons.

It should be noted that the above embodiment can be modified as follows.
-Dryer 11 may not be a square box type like the above-mentioned embodiment, but may be a polygonal cylinder type, a cylindrical type, etc.

The positional relationship among the separator 32, the pressure reducing valve body 33, and the electric heater 34 is not limited to the configuration of the embodiment, and may be in any order.
-Other known heating devices such as an IH heater (electromagnetic heater) may be adopted as a heating means in place of the electric heater 34 of the embodiment.

  In the repetition of the lower limit absolute pressure P2 and the upper limit absolute pressure P1, the pressure fluctuation time can be appropriately changed according to the moisture content of the food material, etc., so that the drying efficiency of the food material can be increased.

  In the repetition of the lower limit temperature T2 and the upper limit temperature T1, the temperature variation time can be appropriately changed according to the moisture content of the food material, etc., so that the drying efficiency of the food material can be improved.

  DESCRIPTION OF SYMBOLS 10 ... Drying apparatus of food material weak to heat denaturation, 11 ... Dryer, 16 ... Cooler, 20 ... Decompression unit, 30 ... Low-temperature steam generation unit, 34 ... Electric heater, P1 ... Upper limit absolute pressure, P2 ... Lower limit absolute pressure, T1: upper limit temperature, T2: lower limit temperature.

Claims (6)

When drying a food material that is vulnerable to heat denaturation under reduced pressure, set a lower limit pressure and a lower limit temperature at that time, set an upper limit pressure and an upper limit temperature at that time, lower the pressure to the lower limit pressure, and After evaporating the water and reaching the lower limit temperature, which is the saturation temperature at the lower limit pressure, low-temperature steam at 100 ° C. or less is injected to heat the food material from the lower limit temperature to the upper limit temperature, and the upper limit pressure is reached. A method for drying a food material that is vulnerable to heat denaturation, characterized in that the moisture content of the food material is reduced by repeating this operation. The method for drying a food material vulnerable to thermal denaturation according to claim 1, wherein the low-temperature steam is low-temperature superheated steam. The said lower limit pressure and upper limit pressure are set within the range of 3-92 kPa with an absolute pressure, The drying method of the food material weak to heat denaturation of Claim 1 or Claim 2 characterized by the above-mentioned. A drying apparatus used in the method for drying a food material vulnerable to heat denaturation according to any one of claims 1 to 3,
A drying cabinet for containing and drying food materials vulnerable to heat denaturation, and lowering the pressure in the drying cabinet to a lower limit pressure to evaporate the moisture of the food material to a lower limit temperature which is a saturation temperature at the lower limit pressure A decompression unit for reaching, and a low-temperature steam generation unit for injecting low-temperature steam into the drying chamber and heating the food material from the lower limit temperature to the upper limit temperature to reach the upper limit pressure. Drying equipment for food materials that are vulnerable to heat denaturation. The apparatus for drying food materials vulnerable to heat denaturation according to claim 4, wherein the low-temperature steam generation unit includes an electric heater for heating the low-temperature steam to generate low-temperature superheated steam. 6. The drying apparatus for food materials vulnerable to thermal denaturation according to claim 4, wherein a cooler for cooling water vapor is provided in the drying cabinet.

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