Sales methods for food products including rice

Abstract

Food products, including cooked rice, are frozen to a high quality standard, then thawed at room temperature in an unopened state to ensure high quality before being sold. [Solution] A method for selling food products including cooked rice, comprising: a manufacturing step S10; a packaging step S20; a freezing step S30; a cooling step S35 after steps S10, S20, and S30, in which the food is kept in a frozen state below a predetermined temperature; a thawing step S40 after the cooling step S35, in which the food is thawed to room temperature while remaining unopened; and a display step S50 after the thawing step S40, in which the thawed food 60 is placed in a location in a sales store 70 where it can be seen by at least the purchaser 80. In the freezing step S30, the cooked rice is rapidly frozen so that it passes through a temperature range of 0°C to 5°C within 15 minutes and through a temperature range of -5°C to -1°C within 60 minutes.

Description

Technical Field

[0001] The present technology relates to a method for selling food containing cooked rice.

Background Art

[0002] Conventionally, it has been widely practiced that frozen foods are sold at stores, and purchasers (customers) cook them by heating using a microwave oven. Patent Document 1 describes a method for maintaining good taste when rapidly freezing cooked rice as a food material.

[0003] The method for producing frozen food ingredients described in Patent Document 1 encloses water together with raw rice in a container, and rapidly freezes the sealed container. It is also described that, when cooling from room temperature to freezing temperature in rapid freezing, it is preferable that the temperature of the food material at the center in the container passes through the maximum ice crystal formation zone of -5°C to -1°C in a short time (within 5 minutes). This is said to effectively suppress the outflow of umami components from the water-absorbed rice in the container.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] In the method described in Patent Document 1, the rapidly frozen rice is removed from the container and heated using a microwave oven or rice cooker. Conventional frozen rice is intended to be heated in this way and consumed immediately afterward. For example, frozen rice heated in a microwave oven in a retail store may deteriorate in quality or develop bacterial growth if left for a period of time, so it is preferable to consume it immediately in the store's eat-in area. For this reason, heated frozen rice is not suitable for use in situations such as purchasing it in the morning before going to work and eating it at the workplace at lunchtime, and is not used as a substitute for food products that are displayed at room temperature.

[0006] Therefore, one might consider thawing frozen cooked rice at room temperature (around 20°C) rather than heating it to the temperature range where bacteria are most likely to multiply (around 30°C to 40°C). However, in that case, the cooked rice tends to become dry and hard, resulting in a decrease in quality.

[0007] This technology was developed in consideration of the circumstances described above, and aims to freeze food products, including cooked rice, to a high quality standard, and then thaw them at room temperature while remaining unopened to enable high-quality thawing and sale. [Means for solving the problem]

[0008] The sales method for food products related to this technology is as follows: A method of selling food products including cooked rice, A manufacturing step for processing and manufacturing the aforementioned food product, A packaging step of packaging the aforementioned food, A freezing step in which the aforementioned food is rapidly frozen, Following the manufacturing step, the packaging step, and the freezing step, there is a cooling step in which the food is kept in a frozen state at a predetermined temperature or below. The thawing step, which follows the aforementioned refrigeration step, involves thawing the food product while keeping it unopened until it reaches room temperature. The process includes, after the thawing step, a display step of placing the thawed food in a location within the store where it can be seen by at least one customer, In the freezing step, the cooked rice is rapidly frozen so that it passes through the temperature range of 0°C to 5°C within 15 minutes and through the temperature range of -5°C to -1°C within 60 minutes.

[0009] Furthermore, in the cooling step, the cooked rice may always be kept at -20°C or below.

[0010] Furthermore, in the thawing step, The aforementioned food is thawed by irradiating it with microwaves under a vacuum state lower than atmospheric pressure using a vacuum microwave thawing machine. The target vacuum level in the thawing operation of the vacuum microwave thawing machine may be set within a predetermined range. [Effects of the Invention]

[0011] This technology allows for the high-quality freezing of food products, including cooked rice, and then high-quality thawing at room temperature while remaining unopened before sale. [Brief explanation of the drawing]

[0012] [Figure 1] Diagram showing the flow of the food sales method according to Embodiment 1 [Figure 2] Front view of a vacuum microwave thawing machine [Figure 3] Figure 2 shows a cross-sectional view of the vacuum microwave thawing machine (Line II). [Figure 4] Figure 3 shows a cross-sectional view of the vacuum microwave thawing machine shown in Figure 2, cut along the line II-II. [Figure 5] Graph showing the temperature changes of Examples 1 and 2 (rice balls) in the evaluation experiment. [Figure 6] Graph showing temperature change in Example 3 (bento box) in the evaluation experiment. [Modes for carrying out the invention]

[0013] <Embodiment 1> A method for selling food containing cooked rice according to Embodiment 1 will be described with reference to FIGS. 1 to 6. The type of food to be sold in the present embodiment is not limited as long as it is a so-called ready meal that contains cooked rice and can be eaten without additional cooking. Examples include onigiri made from cooked rice, and lunch boxes containing cooked rice and side dishes.

[0014] As shown in FIG. 1, the food selling method according to the present embodiment includes a manufacturing step S10, a packaging step S20, a freezing step S30, a cold-holding step S35, a thawing step S40, and a display step S50. The manufacturing step S10 is a process of processing and cooking raw materials to manufacture food. The packaging step S20 is a process of packaging the manufactured food. The packaging form may be sealed or unsealed.

[0015] Specific implementation details of the manufacturing step S10 and the packaging step S20 are not limited, and the steps can be performed using various conventionally known methods and implementation means. Therefore, for example, the implementation details of the manufacturing step S10 and the packaging step S20 may be the same as those in a case where the food is shipped from a manufacturing base as food for normal-temperature display without performing the freezing step S30.

[0016] The freezing step S30 is a step of rapidly freezing the manufactured food. The freezing step S30 is preferably performed after the packaging step S20. This can suppress drying of the food in the freezing step S30. In the freezing step S30, rapid freezing is performed such that the cooked rice contained in the food passes through the temperature range of 0°C to 5°C within 15 minutes, and passes through the temperature range of -5°C to -1°C within 60 minutes. The reason for this will be described below.

[0017] It is known that starch contained in rice changes from a beta state to an alpha state through cooking, resulting in a high-quality state that is soft, sticky, transparent, and glossy. Additionally, it is known that when gelatinized (alpha) starch passes through a temperature range of 0°C to 5°C during the cooling process, it crystallizes and returns to the beta state. When starch returns to the beta state, the cooked rice loses its transparency and gloss, becomes dry and hard.

[0018] Therefore, in the present embodiment, in freezing step S30, quick-freezing is performed so that the rice passes through the beta transition temperature range (0°C to 5°C) in a short time (specifically, within 15 minutes). This method maintains the alpha state of starch and allows cooked rice to be frozen while maintaining high quality.

[0019] It is also known that ice contained in food destroys tissue within the food when passing through the maximum ice crystal formation temperature range (-5°C to -1°C). Therefore, in freezing step S30, by performing quick-freezing such that the food passes through the maximum ice crystal formation temperature range within a predetermined time (specifically, within 60 minutes), freezing can be achieved with higher quality.

[0020] The means for implementing freezing step S30 is not limited as long as it can achieve quick-freezing that passes through the beta transition temperature range and the maximum ice crystal formation temperature range within the aforementioned time. Examples include blast chillers that use cold air for quick-freezing, and liquid freezers that use liquid for quick-freezing. Ordinary freezers are incapable of such quick-freezing, leading to degradation of starch into the beta state and destruction of food tissue by ice crystals, making high-quality freezing difficult to achieve.

[0021] The cooling step S35 is a process that takes place after the freezing step S30 and keeps the packaged and frozen food in a frozen state below a predetermined temperature. In the cooling step S35, it is preferable to keep the cooked rice at -20°C or below at all times. Even if the food is frozen to a high quality using the freezing step S30 described above, if the temperature rises temporarily after freezing, there is a concern that thawing will progress and the quality will deteriorate. Specifically, repeated freezing and thawing can cause moisture to be lost and the cooked rice to become spongy. Keeping the cooked rice at -20°C or below at all times can reliably prevent this from happening.

[0022] The thawing step S40 is a process of thawing frozen food to room temperature while keeping it unopened. The means of carrying out the thawing step S40 are not limited to any method that can thaw the food to room temperature while suppressing overheating. For example, refrigerated thawing, where the food is stored in a refrigerator; water thawing, where the food is placed under running water or ice water; vacuum thawing, where the food is placed under vacuum; heating thawing, where the food is placed in a microwave oven; high-voltage thawing, where electrical energy is generated by high-voltage electrostatic induction; high-frequency thawing, where high-frequency energy is used; or a combination of these, such as vacuum microwave thawing, can be used.

[0023] In this embodiment, a method for performing the thawing step S40 using a vacuum microwave thawing machine 10 is illustrated. The vacuum microwave thawing machine 10 is a device that includes a chamber 11 for containing frozen food and thaws the frozen food in the chamber 11, which has been reduced to a vacuum state below atmospheric pressure, by irradiating it with microwaves. The vacuum microwave thawing machine 10 will be described in detail later.

[0024] As shown in Figure 1, the manufacturing step S10, packaging step S20, and freezing step S30 are performed at a manufacturing base 30 (such as a food manufacturing plant or central kitchen) that manufactures bento boxes for sale at multiple first sales outlets 70 in one place. The thawing step S40 is performed at the sales outlets 70. In this embodiment, the sales outlets 70 are assumed to be, for example, convenience stores or supermarkets, but are not limited to any place where food can be sold. For example, the sales outlets 70 may be sales booths inside train cars, sales spaces set up in baseball stadiums, or even mobile stores.

[0025] Food products are delivered from the manufacturing base 30 to the sales store 70 by a transport vehicle 35 (an example of transport equipment). Delivery to the sales store 70 by the transport vehicle 35 is not limited to a direct route; it may also be delivered via an intermediate facility (e.g., a distribution center). The food products delivered to the sales store 70 may be thawed immediately after being unloaded from the transport vehicle 35 (i.e., the thawing step S40 may be performed), or they may be stored frozen within the sales store 70 and then thawed at any time depending on sales conditions, inventory conditions, etc. (i.e., the thawing step S40 may be performed at any time after the refrigeration step S35).

[0026] The refrigeration step S35 is performed continuously between the freezing step S30 and the thawing step S40. In Figure 1, the locations where the refrigeration step S35 is performed are the manufacturing base 30, the transport vehicle 35, and the sales store 70. However, if the food is shipped from the manufacturing base 30 immediately after the freezing step S30, the refrigeration step S35 does not need to be performed at the manufacturing base 30. Also, if the thawing step S40 is performed immediately after unloading from the transport vehicle 35, the refrigeration step S35 does not need to be performed at the sales store 70.

[0027] The food is thawed using a vacuum microwave thawing machine 10 for display at the retail store 70. More specifically, the staff of the retail store 70 place the frozen food into the chamber 11 of the vacuum microwave thawing machine 10 and operate the control unit 25 of the vacuum microwave thawing machine 10, which will be described later. At this time, the frozen food remains in its packaging and is not opened. The frozen food is thawed by the vacuum microwave thawing machine 10 to room temperature while remaining unopened. The thawed food is then removed from the vacuum microwave thawing machine 10 by the staff.

[0028] Here, "room temperature" in this specification refers to a temperature range of approximately 15°C to 25°C. Therefore, "room temperature sales" in this specification includes not only cases where the product is sold at the ambient temperature (room temperature) within the sales store 70, but also cases where the product is sold in a temperature-controlled state (refrigerated, etc.) within this temperature range, depending on the summer environment of the sales store 70.

[0029] In display step S50, unopened food products that have been thawed at room temperature are placed on display shelves by store staff. Customers then select and purchase the displayed food products.

[0030] The location where thawed food is displayed here does not need to be a place where the food can be seen by the customer, but is not limited to a place where the customer can directly touch the food. For example, it is acceptable for a store employee to take the food from the display shelf and hand it to the customer upon request. It is also acceptable for a system to be in place where the customer's purchase request is communicated to the store employee using an information and communication terminal.

[0031] Next, the configuration of the vacuum microwave thawing machine 10 and the thawing method will be explained with reference to Figures 2 to 4. The vacuum microwave thawing machine 10 broadly comprises a chamber 11, a door 12, a vacuum pump 13 for reducing the pressure inside the chamber 11, a control valve 14 for restoring (boosting) the pressure inside the chamber 11, a vacuum sensor 15 for measuring the pressure (vacuum level) inside the chamber 11, a magnetron 16 (microwave generator) for generating microwaves, a waveguide 17 for guiding microwaves from the magnetron 16 into the chamber 11, a control device 20, and an operating unit 25. The symbols F, B, L, R, U, and D shown in Figures 2 to 4 indicate the front and rear in the front-to-back direction, left and right in the width direction (left-to-right direction) when viewed from the front, and up and down in the vertical direction (up and down direction), respectively.

[0032] Chamber 11 is a horizontally elongated, roughly rectangular box made of metal such as stainless steel, and its interior serves as a thawing chamber for storing frozen food. Chamber 11 has a front opening 11S1 for storing and removing frozen food, and the front opening 11S1 can be opened and closed by a swing-type door 12.

[0033] The control device 20 includes at least a microcomputer and memory, and controls the operation of the vacuum microwave thawing machine 10 based on a control program. The operation unit 25 is provided for changing various settings and selecting operating modes by the store clerk 71 or the maintenance manager of the vacuum microwave thawing machine 10.

[0034] The vacuum microwave thawing machine 10 thaws frozen food without heating it to high temperatures by repeatedly irradiating it with microwaves while performing a depressurization process and a repressurization process, causing the ice contained in the frozen food to sublimate into water vapor. The ice in the frozen food sublimes into water vapor without undergoing a phase transition to water.

[0035] Therefore, since the vacuum microwave thawing machine 10 thaws food in a pressure and temperature range where water cannot exist, it is possible to suppress the generation of drip (moisture containing flavor components, etc., that flows out of the food) that occurs when thawing frozen food. As a result, frozen food can be thawed at room temperature at a low temperature without becoming sticky. Furthermore, even if localized thawing progresses during the thawing process, the water in the thawed area sublimes, generating a cooling effect due to latent heat, thus suppressing excessive heating and reducing uneven thawing (uneven heating). In addition, as the ice contained in the frozen food passes through the maximum ice crystal formation temperature range, the ice sublimes and is removed as water vapor, making it less likely for the food's structure to be damaged by ice crystals.

[0036] The vacuum microwave thawing machine 10 has conventionally been used to thaw frozen fresh seafood in a temperature range below 0°C for sale in supermarkets, etc., for raw consumption such as sashimi (for example, thawing from a freezing temperature range of approximately -60°C to -20°C to a temperature range of approximately -10°C to -5°C). The target vacuum level (pressure inside the chamber 11) in the thawing operation of the vacuum microwave thawing machine 10 is, for example, 3.6 Torr is appropriate when thawing frozen tuna, and for frozen foods including cooked rice, it is preferable to set it to approximately 5.0 Torr to 5.1 Torr (an example within the predetermined range). If the pressure is lower than this range, thawing will be insufficient, and if it is higher than this range, the surface of the cooked rice will dry out.

[0037] According to the sales method for rice-based foods described above, frozen rice-based foods can be frozen to a high standard, thawed at room temperature while unopened, and sold as an equivalent alternative to conventional foods that can be displayed and sold at room temperature. This allows customers to purchase thawed food at one of the 70 stores in the morning before going to work and eat it at their workplace during lunchtime.

[0038] Frozen foods deteriorate less in quality compared to room-temperature foods and can be stored for longer periods, thus reducing the number of deliveries to 70 stores and improving logistics efficiency. This also helps alleviate the increasingly serious problem of a shortage of drivers for 35 transport vehicles. Furthermore, it reduces food waste due to excess inventory. In addition, store staff can thaw frozen foods according to sales trends, reducing lost sales opportunities due to insufficient inventory.

[0039] <Evaluation experiment> An evaluation experiment was conducted to assess the thawing state of food containing cooked rice using the freezing step S30, the cooling step S35, and the thawing step S40 described above. The evaluation experiment is described in detail below.

[0040] <Foods used in the experiment> Onigiri (rice balls) and bento boxes that are normally sold at room temperature (stored) in convenience stores were frozen unopened. Generally, onigiri sold in convenience stores come in three types: 1) those without seaweed, 2) those with seaweed in contact with the rice and in a moist state, and 3) those with seaweed packaged so that it does not come into contact with the rice and is in a dry state. In this experiment, onigiri of types 2) and 3), which are difficult to thaw in high quality, were designated as Examples 1 and 2. The filling for 2) was mentaiko (spicy cod roe), and the filling for 3) was tuna mayonnaise. An onigiri box was designated as Example 3. The bento box was a so-called Makunouchi bento, and the side dishes included grilled mackerel and croquettes.

[0041] <Specific details of freezing step S30> In the freezing step S30, a blast chiller (manufactured by Hoshizaki Corporation, model number HBC-20B3) was used. Figures 5 and 6 show the changes in the internal temperature (core temperature) of the cooked rice in the food products according to Examples 1 to 3.

[0042] The cooked rice in the rice ball according to Example 1 was rapidly frozen so that it passed through the beta-forming temperature range (temperature range from 0°C to 5°C) in about 8 minutes and the maximum ice crystal formation temperature range (temperature range from -5°C to -1°C) in about 25 minutes (reaching -1°C in about 25 minutes and -5°C in about 50 minutes), as shown in Figure 5. The cooked rice in Example 2 was rapidly frozen so that it passed through the beta-forming temperature range in about 8 minutes and the maximum ice crystal formation temperature range in about 25 minutes (reaching -1°C in about 19 minutes and -5°C in about 44 minutes). The cooked rice in Example 3 was rapidly frozen so that it passed through the beta-forming temperature range in about 15 minutes and the maximum ice crystal formation temperature range in about 26 minutes (reaching -1°C in about 105 minutes and -5°C in about 131 minutes), as shown in Figure 6. Note that Figures 5 and 6 show data on the core temperature of the cooked rice, while the surface temperature of the cooked rice decreased more rapidly.

[0043] <Specific details of the cooling step S35> In the refrigeration step S35, the foods according to Examples 1 to 3 were kept frozen and stored at approximately -25°C.

[0044] <Specific details of thawing step S40> In thawing step S40, the foods according to Examples 1 to 3 were thawed using the vacuum microwave thawing machine 10. For comparison with the vacuum microwave thawing machine 10, refrigeration thawing and heating thawing using a microwave oven were also performed.

[0045] <Evaluation Results> For the food products of Examples 1 to 3, the thawing state was evaluated in terms of the condition of the packaging surface, the condition of the inside of the packaging, the condition of the cooked rice, the condition of ingredients and side dishes other than cooked rice, and temperature unevenness. As a result, it was confirmed that all of the food products of Examples 1 to 3 were in a high-quality state equivalent to that of the room-temperature product before the freezing step S30.

[0046] In comparative experiments using the thawing step S40, it was confirmed that refrigeration thawing took a long time, and heating thawing using a microwave oven resulted in significant temperature unevenness. For example, when thawing rice balls, even when thawing just one rice ball using a microwave oven, a large temperature difference of up to 20.4°C occurred between the surface (top side of chamber 11) and the underside (bottom side of chamber 11) at the end of the thawing process. Furthermore, when thawing 15 rice balls simultaneously, an even larger temperature difference of up to 42.4°C was observed, due to temperature differences depending on the storage location.

[0047] In contrast, when using the vacuum microwave thawing machine 10, even when thawing 15 items simultaneously, it was confirmed that temperature variations were kept to a minimum, with the surface temperature at the end of the thawing operation ranging from 6.9°C to 9.4°C and the internal temperature ranging from 0.1°C to 0.9°C. Furthermore, if the internal temperature at the end of the thawing operation is within this temperature range, it can pass through the beta-conversion temperature range (temperature range of 0°C to 5°C) in about 30 minutes if left at the room temperature environment of the sales store 70 (approximately 15°C to 20°C), so it can be said that beta-conversion (deterioration) of cooked rice that would affect the taste will not occur.

[0048] <Other Embodiments> This technology is not limited to the embodiments described above and in the drawings, and the following embodiments, for example, are also included in the technical scope of this technology.

[0049] (1) Transportation equipment is not limited to transport vehicles such as trucks, but may also include railway cars, airplanes, ships, etc.

[0050] (2) The refrigeration step S30 may be performed during transport to the sales store 70. For example, the blast chiller may be installed inside the transport vehicle 35 and the refrigeration step S30 may be performed inside the transport vehicle 35. Alternatively, if the transport by the transport vehicle 35 is carried out via a relay facility (e.g., a distribution center), the blast chiller may be installed inside the relay facility and the refrigeration step S30 may be performed inside the relay facility. In this way, the refrigeration step S30 can be performed using the transport time, making it more efficient.

[0051] (3) The thawing step S40 may be performed during transport to the sales store 70. For example, the vacuum microwave thawing machine 10 may be installed inside the transport vehicle 35, and the thawing step S40 may be performed inside the transport vehicle 35. Alternatively, if the transport by the transport vehicle 35 is carried out via a relay facility (e.g., a distribution center), the vacuum microwave thawing machine 10 may be installed inside the relay facility, and the thawing step S40 may be performed inside the relay facility. In this way, the thawing step S40 can be performed using the transport time, making it more efficient.

[0052] (4) The configuration of the vacuum microwave thawing machine 10 is not limited as long as it can thaw frozen food using the mechanism described above. For example, the vacuum microwave thawing machine 10 shown in Figures 2 to 4 includes a stirrer 18 that diffuses microwaves into the chamber 11 to suppress uneven heating, and a motor 19 that rotates the stirrer 18. However, these are not provided, and a rotating table on which the frozen food is placed may be provided to suppress uneven heating. [Explanation of Symbols]

[0053] 10: Vacuum microwave thawing machine, 50: Frozen food, 60: Thawed food, 70: Retail store, 80: Buyer, S10: Manufacturing step, S20: Packaging step, S30: Freezing step, S35: Cooling step, S40: Thawing step, S50: Display step

Claims

1. A method of selling food products including cooked rice, A manufacturing step for processing and manufacturing the aforementioned food product, A packaging step of packaging the aforementioned food, A freezing step in which the aforementioned food is rapidly frozen, Following the manufacturing step, the packaging step, and the freezing step, there is a cooling step in which the food is kept in a frozen state at a predetermined temperature or below. The thawing step, which follows the aforementioned refrigeration step, involves thawing the food product while keeping it unopened until it reaches room temperature. The process includes, after the thawing step, a display step of placing the thawed food in a location within the store where it can be seen by at least one customer, A method for selling food, wherein in the freezing step, the cooked rice is rapidly frozen so that it passes through a temperature range of 0°C to 5°C within 15 minutes and through a temperature range of -5°C to -1°C within 60 minutes.

2. The method for selling food according to claim 1, wherein in the refrigeration step, the cooked rice is always kept refrigerated at -20°C or below.

3. In the aforementioned thawing step, The aforementioned food is thawed by irradiating it with microwaves under a vacuum state lower than atmospheric pressure using a vacuum microwave thawing machine. The method for selling food according to claim 1 or 2, wherein the target vacuum level in the thawing operation of the vacuum microwave thawing machine is set within a predetermined range.

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