Packaging method and method for producing frozen food

Abstract

The present invention provides a packaging method that achieves both improved freezing efficiency of a package containing a frozen product and protection of the frozen product within the package once it is frozen, as well as a method for manufacturing frozen food using this packaging method. [Solution] The packaging method includes a solidification step in which a package 100 containing the object to be frozen 1 and carbon dioxide gas sealed in a packaging body 2 is cooled to solidify the carbon dioxide gas.

Description

Technical Field

[0001] The present disclosure relates to a packaging method and a method for manufacturing frozen foods.

Background Art

[0002] Patent Document 1 discloses a packaging method for processed foods and a processed food package packaged by that method. In this packaging method for processed foods, a processed food containing moisture is placed in a packaging container while maintaining the surface temperature of the processed food at 70 to 140°C, and after replacing the inside of this packaging container with a carbon dioxide atmosphere, the packaging container is sealed. In this packaging method for processed foods, since a part of the carbon dioxide permeates through the packaging container and is discharged, and another part is absorbed by the processed food, it is said that it is possible to make the packaging container adhere sufficiently to the processed food without impairing the flavor of the processed food.

[0003] Patent Document 2 discloses a method for manufacturing a sashimi-plated frozen food. In this method for manufacturing a sashimi-plated frozen food, as an example, sashimi of one or more kinds of raw or pre-treated seafood is plated in a container, vacuum-packed with an inner film, frozen, and then gas-filled and packaged with an outer film. This gas-filled packaging can be filled with carbon dioxide gas, nitrogen gas, or a mixed gas of carbon dioxide gas and nitrogen gas in a transparent outer film. This freezing is performed by air blast at -35°C or lower, liquid nitrogen, or liquid carbon dioxide.

[0004] Patent Document 3 discloses a method for manufacturing frozen foods. In this method, food ingredients contained in a package are immersed in liquid nitrogen so that the space occupancy rate of the package is 24-76%, and then the package is frozen for storage. This method of manufacturing frozen foods is said to reduce damage to the food ingredients during freezing by liquid nitrogen immersion freezing, and to prevent deterioration of the food ingredients that may occur during the packaging process after freezing because the package is frozen together. Furthermore, this method of manufacturing frozen foods is said to allow for freezing and storage of the food ingredients in their original arrangement, and to prevent the inclusion of food fragments, thus enabling the production of visually appealing frozen foods in containers using a simple procedure.

[0005] Patent Document 4 discloses a frozen food and a method for manufacturing a frozen food. In this method for manufacturing a frozen food, dried fish is frozen using the following procedure: The dried fish is placed in a package, the package is evacuated, and then nitrogen gas, carbon dioxide, or a mixture of nitrogen gas and carbon dioxide is filled into the package. After filling, the package is sealed. After sealing, the dried fish is frozen through the package. In this method for manufacturing a frozen food, the amount of gas filled into the package is such that it adheres tightly to the dried fish and prevents the dried fish from moving within the package. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. H10-225267 [Patent Document 2] Japanese Patent Publication No. 2005-95095 [Patent Document 3] Japanese Patent Publication No. 2018-50557 [Patent Document 4] Japanese Patent Publication No. 2019-187308 [Overview of the project] [Problems that the invention aims to solve]

[0007] When frozen foods, such as those intended for freezing, are frozen without packaging, the frozen foods may be damaged or deteriorated during the freezing process. For example, exposure to the cold air used for freezing may cause the shape of the frozen foods to break or moisture to evaporate. In addition, frost may adhere directly to the frozen foods after they have frozen. Therefore, frozen foods, such as those intended for freezing, may be frozen in a packaged state, that is, in a packaged state enclosed in a packaging body such as a packaging container, as disclosed in the above-mentioned Patent Documents 1 to 4.

[0008] When freezing an object to be frozen by cooling a package containing the object to be frozen, as disclosed in Patent Documents 1 to 4, if the package is in sufficient contact with the object to be frozen, the object is not insulated by the gas inside the package, and the object can be frozen efficiently. For example, if the package is vacuum-packed, the package is in sufficient contact with the object to be frozen, resulting in efficient freezing. However, depending on the characteristics of the object to be frozen, it may be preferable for the object to be frozen with sufficient gas inside the package to protect it from shocks such as vibrations during transport. Therefore, there is a need for a packaging method that can improve the efficiency of freezing a package containing an object to be frozen and protect the object in the package once it is frozen, particularly a packaging method when the object to be frozen is food, that is, a method for manufacturing frozen food.

[0009] This disclosure has been made in view of the circumstances described herein, and its purpose is to provide a packaging method that achieves both improved freezing efficiency of a package containing an object to be frozen and protection of the object to be frozen within the package once it is frozen, and a method for producing frozen food using this packaging method. [Means for solving the problem]

[0010] The packaging method relating to this disclosure for achieving the above objective is: The process includes a solidification step in which a package containing the object to be frozen and carbon dioxide is cooled to solidify the carbon dioxide.

[0011] The method for manufacturing a frozen food according to the present disclosure for achieving the above object includes: a solidification step of cooling a packaging object in which a food to be frozen and carbon dioxide gas are enclosed in a package to solidify the carbon dioxide gas.

Effects of the Invention

[0012] According to the present disclosure, it is possible to provide a packaging method that achieves both an improvement in the efficiency of freezing a packaging object in which an object to be frozen is enclosed in a package and protection of the object to be frozen in the package in which the object to be frozen is frozen, and a method for manufacturing a frozen food by this packaging method.

Brief Description of the Drawings

[0013] [Figure 1] It is an explanatory diagram of the accommodation step. [Figure 2] It is an explanatory diagram of the evacuation step. [Figure 3] It is an explanatory diagram of the gas filling step. [Figure 4] It is an explanatory diagram of the solidification step. [Figure 5] It is an explanatory diagram of the vaporization step. [Figure 6] It is a diagram showing the flow of liquid nitrogen and nitrogen gas in the freezer used in the experimental example. [Figure 7] It is an explanatory diagram of the configuration inside the freezer used in the experimental example. [Figure 8] It is a photograph of the appearance of the package in Experiment 4 after freezing. [Figure 9] It is a photograph of the appearance of the package in Experiment 8 after freezing.

Modes for Carrying Out the Invention

[0014] The packaging method and the method for manufacturing a frozen food according to the embodiment of the present disclosure will be described while referring to the drawings.

[0015] First, an overview of the packaging method according to the present embodiment and the method for manufacturing a frozen food according to the present embodiment will be described.

[0016] The packaging method according to this embodiment includes a solidification step of cooling a packaged object in which a freezing target and carbon dioxide gas are enclosed in a package to solidify the carbon dioxide gas.

[0017] The method for manufacturing a frozen food according to this embodiment includes a solidification step of cooling a packaged object in which a frozen target food and carbon dioxide gas are enclosed in a package to solidify the carbon dioxide gas. The method for manufacturing a frozen food according to this embodiment is realized by the packaging method according to this embodiment.

[0018] According to the packaging method according to this embodiment, it is possible to achieve both an improvement in the efficiency of freezing a packaged object in which a freezing target is enclosed in a package and the protection of the freezing target in the package in which the freezing target is frozen.

[0019] According to the method for manufacturing a frozen food according to this embodiment, it is possible to achieve both an improvement in the efficiency of freezing a packaged object in which a frozen target food is enclosed in a package and the protection of the food in the package in which the frozen target food is frozen.

[0020] Hereinafter, the packaging method according to this embodiment and the method for manufacturing a frozen food according to this embodiment will be described in detail.

[0021] In this embodiment, the packaged object is an object in which a freezing target and carbon dioxide gas are enclosed in a package. The package in this embodiment is a bag body or a body that can be a bag body having a property (flexibility) of being deformable along the shape of the freezing target. An example of the package is a film-shaped bag body made of a resin resistant to low temperatures, such as polyethylene, polypropylene, polyethylene terephthalate, or nylon.

[0022] The freezing target in this embodiment is an object that is packaged in a flexible package and protected from external impacts, and is an object that is prevented from deteriorating such as spoilage or degradation by freezing and can be stored for a long time.

[0023] Examples of objects to be frozen include solids containing water and organic matter, such as food, cells, biological tissues, and bacterial strains. The object to be frozen may also be packaged in other packaging or containers (e.g., glass bottles such as vials). In this embodiment, when the object to be frozen is food, it is referred to as the food to be frozen.

[0024] Examples of foods that can be frozen include animal products such as meat and fish, plant-based products such as vegetables and fruits, pre-cooked foods such as retort foods, and plated foods.

[0025] The packaging method according to this embodiment may include a gas filling step, a solidification step, and a vaporization step in this order.

[0026] The gas filling process involves sealing carbon dioxide gas into the packaging containing the items to be frozen. In the gas filling process, carbon dioxide gas may be blown into the packaging to replace the air inside the packaging, or the air may be removed from the packaging containing the items to be frozen before blowing carbon dioxide gas into the packaging to seal it. It is desirable that 80% to 100% (for example, 99%) of the air inside the packaging is replaced with carbon dioxide gas in terms of partial pressure.

[0027] In the gas filling process, it is preferable to evacuate the packaging containing the object to be frozen and then fill the packaging with carbon dioxide. This ensures that the gas inside the packaging is replaced with carbon dioxide of high purity, improving the efficiency of cooling the object to be frozen in the solidification process described later.

[0028] When vacuuming a package, it is desirable to reduce its volume to between 95% and 100% (for example, 99%), where the maximum volume of the package containing the items to be frozen (the maximum volume of the package minus the volume of the items to be frozen) is considered 100%. This allows for efficient replacement of the air inside the package with carbon dioxide.

[0029] In the gas filling process, carbon dioxide gas should be sealed into the packaging at a pressure sufficient to maintain at least an inflated state. This protects the contents to be frozen from vibrations and other shocks. If the pressure of the carbon dioxide gas in the packaging is, for example, 100 Pa or more in gauge pressure, the packaging can maintain its inflated state against vibrations during transport and protect the contents to be frozen. For example, if the packaging is subjected to external forces (external pressure) such as other cargo (including other packages) being piled on top of it during transport, or if the packaging is subjected to particularly large vibrations during transport, the pressure of the carbon dioxide gas sealed into the packaging should be increased to withstand these external forces and large vibrations. In most cases, a pressure of 0.2 MPa or less in gauge pressure is sufficient for the carbon dioxide gas sealed into the packaging. That is, in the gas filling process, the pressure of the carbon dioxide gas in the packaging should be between 0.03 MPa and 0.2 MPa in gauge pressure.

[0030] The solidification process involves cooling a package containing the object to be frozen and carbon dioxide gas, causing the carbon dioxide gas to solidify while the object to be frozen is frozen. In the solidification process, the package is cooled in an environment of -78°C or below.

[0031] Cooling methods to achieve an environment below -78°C include, for example, spraying the packaging with a cryogenic liquefied gas or immersing the packaging in a cryogenic liquefied gas. One example of a cryogenic liquefied gas is liquid nitrogen.

[0032] By cooling the packaging in an environment below -78°C, the carbon dioxide gas solidifies into dry ice. This temporarily eliminates the gas inside the packaging, creating a vacuum inside the packaging, causing it to contract and adhere tightly to the object being frozen.

[0033] When the packaging adheres closely to the object to be frozen, the efficiency of cooling the object is improved, allowing the object to be frozen in a shorter time or with less energy.

[0034] In other words, during the solidification process, the carbon dioxide gas sealed in the packaging is converted into dry ice, causing the packaging to shrink and the inner surface of the packaging to adhere tightly to the object to be frozen, thereby improving the freezing efficiency of the object.

[0035] In the solidification process, it is preferable to cool (freeze) the object to be frozen to a temperature of -30°C or higher and -15°C or lower. This effectively suppresses deterioration of the object to be frozen. It is even preferable that the object to be frozen is cooled (freezed) to -18°C or lower during the solidification process.

[0036] The vaporization process involves sublimating the carbon dioxide that has solidified within the packaging. This causes the packaging to expand, protecting the contents from vibrations and other shocks.

[0037] In the vaporization process, the packaged material may be heated to a temperature above -78°C. The vaporization process can be carried out, for example, by storing the packaged material in a freezer or refrigerator at a temperature between -30°C and -15°C.

[0038] During the vaporization process, all the carbon dioxide in the packaging is vaporized, causing the packaging to expand to its state before the solidification process. The pressure of the carbon dioxide in the packaging after the vaporization process is preferably 100 Pa or more and 0.2 MPa or less in gauge pressure, as described in the explanation for the gas filling process.

[0039] In the following, the packaging method according to the embodiment described above will be explained with reference to Figures 1 to 5 in that order. The packaging method according to the embodiment can be carried out as follows as an example. The packaging method according to the embodiment may further include a containment step and a vacuuming step as steps performed before the gas filling step, as will be explained below.

[0040] As shown in Figure 1, first, a packing process is performed in which the object to be frozen 1 is placed in the packaging 2. In this state, air is present in the internal space S of the packaging 2.

[0041] Therefore, as shown in Figure 2, a vacuuming process is performed to evacuate the packaging 2 and remove as much air as possible from the internal space S (see Figure 1). Specifically, it is preferable to evacuate the packaging 2 to the extent that the inner surface of the packaging 2 is in close contact with the object to be frozen 1.

[0042] Then, as shown in Figure 3, a gas filling process is performed in which carbon dioxide gas is sealed into the internal space S of the package 2 after vacuuming. After sealing with carbon dioxide gas, the opening of the package 2 may be sealed by heat sealing or other means. In Figure 3, the heat-sealed portion of the package 2 is shown as the sealing portion 20. Vacuuming of the package 2 and sealing of carbon dioxide gas into the package 2 may be performed using a vacuum packaging machine connected to a carbon dioxide gas supply source such as a gas cylinder.

[0043] Subsequently, as shown in Figure 4, the package 100, which contains the object to be frozen 1 and carbon dioxide gas sealed in the packaging 2, is placed inside, for example, the first freezer 4. In the first freezer 4, a solidification process is performed in which the package 100 is cooled by exposing it to an environment of -78°C or lower, for example, using liquid nitrogen. Figure 4 illustrates the case in which liquid nitrogen (low-temperature liquefied gas) is sprayed onto the package 100 from a liquid nitrogen supply nozzle 31 connected to a liquid nitrogen supply source such as a liquid nitrogen cylinder to cool the package 100. This cooling causes the carbon dioxide gas to solidify and change into dry ice, and the packaging 2 shrinks and becomes tightly attached to the object to be frozen 1.

[0044] After the object to be frozen 1 has been cooled to between -30°C and -15°C, for example, the package 100 is removed from the first freezer 4 and transferred to the second freezer 5, as shown in Figure 5. The temperature inside the second freezer 5 is controlled to between -30°C and -15°C. While the package 100 is stored in the second freezer 5, the dry ice sublimes within the packaging 2 of the package 100. As a result, the packaging 2 expands to the state before the carbon dioxide gas solidifies, with the internal space S being filled with carbon dioxide gas again. In other words, inside the second freezer 5, the dry ice inside the packaging 2 sublimes, and a vaporization process is performed that expands the packaging 2 to the state before the solidification process. [Examples]

[0045] The following describes, based on experimental examples, the method for producing frozen food using the packaging method according to this embodiment.

[0046] In the following experiments, a rectangular-shaped yokan (sweet bean jelly) was used as the object to be frozen (the food to be frozen). The yokan used in the following experiments weighed 150g, and its dimensions, when viewed from above, were 50mm on the short side, 76mm on the long side, and 30mm in height.

[0047] First, the yokan was subjected to the following conditions: in its unpackaged state (Condition 1), in a vacuum-sealed package (Condition 2), in a package filled with air (Condition 3), and in a package filled with carbon dioxide gas according to the packaging method of this embodiment (Condition 4).

[0048] The packaging under condition 2 involved placing the package containing the yokan into a vacuum packaging machine, performing a vacuum, and then sealing the opening of the package.

[0049] For packaging under condition 3, the packaging containing the yokan was placed in a vacuum packaging machine, vacuuming was performed, then air was re-sealed into the packaging (0.1 MPaG), and the opening of the packaging was sealed.

[0050] The packaging under condition 4 involved placing the packaging containing the yokan into a vacuum packaging machine, performing a vacuum evacuation, then sealing the packaging with carbon dioxide gas (0.1 MPaG), and finally sealing the opening of the packaging.

[0051] Furthermore, a T-type thermocouple (Class 2) was inserted (embedded) in the center of each of the yokan samples from Condition 1 to Condition 4, allowing for measurement of the temperature at the center of the yokan. In the following explanation, the temperature of the yokan refers to the temperature measured by this thermocouple.

[0052] In the following, packaging under condition 1 may be referred to as "unpackaged," packaging under condition 2 as "vacuum-packaged," packaging under condition 3 as "air-packaged," and packaging under condition 4 as "carbon dioxide-packaged."

[0053] Next, the yokan (sweet bean jelly) under conditions 1 to 4 were placed in a freezer (liquid nitrogen type freezer, manufactured by TALLERES VICENTE MERINO, Sa, model CRYOSAN CABINET FREEZER AR-22494) set to an internal temperature of -60°C (-60°C, Experiments 1 to 4) or -90°C (-90°C, Experiments 5 to 8) and cooled (frozen). Experiment 8 is an example conducted under conditions according to the packaging method of this embodiment, while Experiments 1 to 7 are comparative examples that do not follow these conditions.

[0054] The fan inside the freezer was set to an output frequency of 50Hz, and liquid nitrogen was used for cooling.

[0055] Here, we will explain the general configuration of the freezer used in this experiment. Figures 6 and 7 show the schematic configuration of the freezer used in this experiment (freezer 4 in Figures 6 and 7).

[0056] Figure 6 shows the flow of liquid nitrogen and nitrogen gas in the freezer used in this experiment. As shown in Figure 6, the freezer 4 is supplied with liquid nitrogen from the liquid nitrogen supply source 3. The liquid nitrogen supplied from the liquid nitrogen supply source 3 into the freezer 4 cools the inside of the freezer, vaporizes, and is then exhausted out of the system through the exhaust port 49 of the freezer 4.

[0057] Figure 7 shows an explanatory diagram (a side view) of the internal configuration of the freezer 4 used in this experimental example. Liquid nitrogen supplied from the liquid nitrogen supply source 3 (see Figure 6) is supplied into the freezer 4 via a liquid nitrogen supply nozzle 31. A shelf 41 is installed inside the freezer 4, on which a tray 91 containing the object to be cooled (in this example, yokan under conditions 1 to 4) can be placed. The fan 45 inside the freezer 4 is for stirring the atmosphere inside the freezer.

[0058] Table 1 shows the experimental conditions (packaging, internal temperature) and results for Experiments 1 through 8. In Table 1, the experimental results for Experiments 1 through 8 show the time from when the yokan under conditions 1 through 4 was placed in the refrigerator until the temperature of the yokan reached -20°C, which is defined as "-20°C arrival time". Hereafter, "-20°C arrival time" will simply be referred to as "arrival time".

[0059] [Table 1]

[0060] As shown in Table 1, the arrival time was longer when the packaging was air-packed (Condition 2) (Experiments 3, 6) than when the packaging was unpacked (Condition 1) (Experiments 1, 5) or vacuum-packed (Condition 3) (Experiments 2, 7).

[0061] These results show that when the packaging is not in close contact with the object to be cooled (yokan), the air inside the packaging acts as an insulator, increasing the time required to cool (freeze) the object and reducing the efficiency of freezing.

[0062] The following is observed when the packaging is in the form of carbon dioxide packaging (condition 4) (Experiments 4 and 8).

[0063] When the internal temperature was -60°C (Experiment 4), the time to reach the target temperature was longer than when the product was unpackaged (Condition 1) (Experiment 1) or vacuum-packed (Condition 3) (Experiment 2), similar to when the product was air-packed (Condition 2) (Experiment 3).

[0064] However, when the internal temperature was -90°C (Experiment 8), the time to reach the target was shorter than when the packaging was air-packed (Condition 2) (Experiment 7), and it was possible to achieve a similar time to when it was vacuum-packed (Condition 3) (Experiment 6).

[0065] These results show that, in the case of carbon dioxide packaging (condition 4), cooling the packaged items to a temperature inside the refrigerator at which carbon dioxide solidifies (below -78°C) shortens the time required to cool (freeze) the items being cooled, thus improving the efficiency of freezing.

[0066] The results of visual observation of the cooling process in Experiments 4 and 8 are as follows. Figures 8 and 9 show photographs of the appearance of each package after freezing (after the temperature of the yokan reached minus 20°C), respectively. In Figures 8 and 9, following the explanations in Figures 1 to 5 and Figure 7, the package is indicated by reference numeral 100, the yokan being cooled is indicated by reference numeral 1, the packaging is indicated by reference numeral 2, and the tray is indicated by reference numeral 91.

[0067] When the internal temperature was -90°C (Experiment 8), we observed that the packaging contracted after being placed inside the refrigerator. After freezing, the packaging completely contracted and adhered tightly to the object being cooled (yokan) (see Figure 9). However, when the internal temperature was -60°C (Experiment 4), the packaging did not contract even after freezing (see Figure 8).

[0068] Based on the experimental results shown in Table 1 and the observations shown in Figures 8 and 9, it can be inferred that in the case of carbon dioxide packaging (Experiment 8), carbon dioxide (gas), which can act as an insulator similar to air in the case of air packaging (Experiment 7) in environments above -78°C, changes into dry ice (solid) in environments below -78°C, thereby reducing the volume of gas inside the packaging and improving the rate of heat transfer. In particular, in Experiment 8 of this experimental example, the volume of gas inside the packaging decreased and the packaging adhered closely to the object to be cooled (yokan), so it is thought that a freezing efficiency comparable to that of vacuum packaging (Experiment 6) was achieved.

[0069] In addition, although not directly apparent from the results shown in Table 1 alone, in cases where the packaging was air-packed (Condition 2) (Experiments 3, 6), vacuum-packed (Condition 3) (Experiments 2, 7), and carbon dioxide-packed (Condition 4) (Experiments 4, 8), the yokan (sweet bean jelly) being frozen was encased in the packaging, which was expected to suppress deformation caused by cold air (nitrogen gas produced from liquid nitrogen or fan wind) during freezing.

[0070] The packages from Experiments 6 through 8 were then moved to a storage freezer (internal temperature -20°C) intended for long-term storage or storage during delivery, and changes over time were observed.

[0071] The packaging from Experiment 8, which used carbon dioxide packaging, rapidly expanded after being moved to the storage freezer. This created a gap between the packaging and the yokan (sweet bean jelly). The packaging from Experiment 8 expanded to the same extent as it was before the yokan was frozen. No particular changes were observed in the packaging from Experiment 6 (vacuum packaging) and Experiment 7 (air packaging).

[0072] In Experiment 8 on carbon dioxide packaging, it is believed that the packaging expanded because the carbon dioxide inside the packaging changed from a solid (dry ice) to a gas under the temperature conditions inside the storage freezer (an environment exceeding -78°C).

[0073] In the inflated packaging of Experiment 8, the inflated packaging is expected to act as a cushioning material inside the storage freezer, similar to the packaging of Experiment 7 which was air-packed, thereby reducing the impact on the yokan (sweet bean jelly) being frozen.

[0074] In Experiment 6, which uses vacuum packaging, the packaging is in close contact with the yokan (sweet bean jelly) being frozen. As a result, the packaging cannot be expected to act as a cushioning material, leaving the yokan vulnerable to direct impact.

[0075] As described above, it is possible to provide a packaging method that achieves both improved freezing efficiency of a package containing the object to be frozen and protection of the object to be frozen within the package once it is frozen, as well as a method for producing frozen food using this packaging method.

[0076] [Another embodiment] (1) In the above embodiment, it was explained that the containment step and the vacuuming step may be further included as steps performed before the gas filling step. However, in the packaging method according to this embodiment, the containment step and the vacuuming step are not essential steps, and the steps after the gas filling step can be performed separately from the containment step and the vacuuming step.

[0077] (2) In the above embodiment, the case in which a vacuuming process is performed after the containment process and then a gas filling process is performed was described as an example. However, the vacuuming process is not an essential process when performing the gas filling process, and the gas filling process may be performed on a package that has not been vacuumed. As described in the above embodiment, in the gas filling process, it is sufficient that the air inside the package is replaced with carbon dioxide.

[0078] The embodiments disclosed herein are illustrative and not limited to those described herein. They may be modified as appropriate without departing from the purpose of this disclosure. [Industrial applicability]

[0079] This disclosure is applicable to packaging methods and methods for manufacturing frozen foods. [Explanation of symbols]

[0080] 1: Items subject to freezing 100: Packaging 2: Packaging 20: Sealing section 3: Liquid nitrogen supply source 31: Nozzle 4: Freezer 41: Shelf 45: Fan 49: Exhaust vent 5: Freezer 91: Tray S:Internal space

Claims

1. A packaging method comprising a solidification step of cooling a package containing an object to be frozen and carbon dioxide gas to solidify the carbon dioxide gas.

2. The packaging method according to claim 1, further comprising a vaporization step of sublimating the solidified carbon dioxide.

3. In the solidification step, the packaging is shrunk, The packaging method according to claim 2, wherein the vaporization step expands the packaging to the state before the solidification step.

4. The packaging method according to claim 1 or 2, further comprising a gas sealing step of evacuating the packaging containing the object to be frozen and then sealing the carbon dioxide gas into the packaging.

5. The packaging method according to claim 1 or 2, wherein the pressure of the carbon dioxide gas in the packaging is 100 Pa or more and 0.2 MPa or less, in gauge pressure.

6. The packaging method according to claim 1 or 2, wherein in the solidification step, the inner surface of the packaging body is in close contact with the object to be frozen.

7. The packaging method according to claim 1 or 2, wherein the object to be frozen is a food product.

8. The packaging method according to claim 1 or 2, wherein the solidification step is cooled in an environment of minus 78°C or lower.

9. The packaging method according to claim 1 or 2, wherein in the solidification step, the object to be frozen is cooled to a temperature of -30°C or higher and -18°C or lower.

10. The packaging method according to claim 1 or 2, wherein in the solidification step, a low-temperature liquefied gas is sprayed onto the packaging to solidify the carbon dioxide gas.

11. A method for producing frozen food, comprising a coagulation step of cooling a package containing food to be frozen and carbon dioxide gas sealed in the package to solidify the carbon dioxide gas.

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