Manufacturing method for dried rice products

Abstract

The objective is to establish a simple pretreatment technique that can achieve the same effect as freeze-drying, which is the conventional pretreatment method that is essential and difficult to control the temperature of, when producing instant dried rice that rapidly absorbs water and recovers when hot water is poured on it. [Solution] One method involves steaming rice to absorb water containing carbonate or bicarbonate, then adding water containing acid and cooking it. The second method involves rapidly freezing the water-soaked steamed rice, then adding water and cooking it. The processed rice product prepared in this way is then dried by freeze-drying. Thus, it becomes possible to produce dried rice that rapidly absorbs water and regenerates when hot water is added, as desired.

Description

Technical Field

[0001] The present invention relates to a dried food, and more particularly to a method for producing an instant dried rice food that can rapidly absorb water and recover by pouring hot water.

Background Art

[0002] Many commercially available dried rice foods are already on the market. Among them, products that absorb water and recover within a few minutes by pouring hot water are produced by the freeze-drying method. The present invention relates to an improvement in the method for producing this type of dried rice product.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Patent Document 11

Patent Document 12

Patent Document 13

Patent Document 14

[0004] [Non-Patent Document 1] Journal of the Japan Society of Home Economics, Vol. 43 (12), 1201-1206 (1992) [Non-Patent Document 2] Journal of the Japan Society of Home Economics, Vol. 52(5), 401-409 (2001) [Overview of the project] [Problems that the invention aims to solve]

[0005] Vacuum freeze-drying preserves the flavor, color, and aroma of undried food or cooked food because the drying process takes place in a frozen state. It is said that when hot water is added, the food rapidly absorbs water and returns to its pre-dried state. These characteristics are often suitable for vacuum freeze-dried products of vegetables, meats, and soups.

[0006] However, it is well known that vacuum freeze-dried rice products such as rice dishes, porridge, and gruel have difficulty with water absorption and recovery when hot water is added. Vacuum freeze-drying requires pre-freezing before drying, but since pre-freezing takes a long time, some of the starch in the rice that has been gelatinized by the heating and addition of water during the cooking stage changes to the poorly water-soluble beta type by the time freezing is complete. Furthermore, it is thought that the slimy component, or stickiness, that is produced during cooking absorbs water and recovers before the rice grains when hot water is added, immediately covering the surface of the rice grains and forming a resistance film against water penetration into the rice grains, which hinders water absorption and recovery.

[0007] On the other hand, due to social trends such as an aging population, an increase in single-person households, and the outsourcing of cooking due to women's increased participation in the workforce, the need for instant rice-based foods is on the rise.

[0008] To meet these social needs, various technologies have been devised to improve the water absorption and resilience of vacuum freeze-dried rice products when hot water is added. For example, Patent Document 1 presents a method to make the inside of the rice grains porous by roasting the rice, thereby facilitating water absorption into the dried rice grains. However, pre-roasting the rice results in a texture of rice after resilience that differs significantly from that of rice prepared using conventional cooking methods.

[0009] Techniques have also been proposed to remove the stickiness produced during rice cooking before drying. For example, Patent Document 9 presents a method of adding water to cooked rice after cooking to wash away the stickiness. However, this method requires the steps of cooling, adding water, stirring, and draining the soft cooked rice after cooking, which is expected to cause difficulties in mass production, such as the breaking of rice grains and gelatinization. Furthermore, the unique flavor and texture of cooked rice are also compromised.

[0010] Since the sticky substance is a concentrated solution of gelatinized starch (see Non-Patent Documents 1 and 2), Patent Document 13 discloses a technique for breaking it down by adding a heat-resistant starch-degrading enzyme during the rice cooking process. However, this technique has drawbacks, including the difficulty in obtaining heat-resistant starch-degrading enzymes (they are special biochemical products and are expensive), and the fact that the enzymes are microbial-derived proteins and may be allergens.

[0011] Patent Document 5 discloses a technique for heating and hydrating rice by steaming rather than boiling, focusing on the fact that stickiness occurs during rice cooking. However, since the moisture content of cooked rice achieved by steaming is lower than that achieved by boiling, the technique disclosed in the patent document requires a very cumbersome procedure of repeatedly sprinkling water while steaming. It is predicted that this would pose significant difficulties for mass production.

[0012] Since the body of rice is composed not only of starch but also of protein, a technique of adding protease to rice during water absorption prior to cooking (when soaking in water after washing) is disclosed in Patent Documents 6 and 10, with the intention of weakening the rice grain body and promoting the formation of ice crystal pores during pre-freezing. However, this also presents the same problems as the addition of starch-degrading enzymes mentioned above.

[0013] From the perspective of the porousness of rice grains, prior to vacuum freeze-drying, ice crystal formation due to the freezing of the inside of cooked rice during preliminary freezing realizes a certain degree of porousness. Vacuum freeze-drying requires slow heating (intense heating will cause the frozen state to collapse and not be in a vacuum freeze-drying state), and it takes a long time for drying. In terms of managing the production time, it is desirable to complete the preliminary freezing in the shortest possible time. As preliminary freezing conditions, air blast with an ambient temperature of about -30 to -50 °C is common. On the other hand, it is speculated that the faster the freezing, the finer the ice crystals inside the cooked rice, and the dried tissue becomes denser and resistant to water absorption and restoration.

[0014] Here, a technique of applying slow freezing to preliminary freezing has become widespread. For example, Patent Documents 7, 8, 9, 12, and 13 describe the adoption of slow freezing. However, unfortunately, slow freezing conflicts with the requirement of production time management to complete the preliminary freezing in the shortest possible time.

[0015] However, according to Patent Document 12, there is a description that the application of slow freezing is common sense in the vacuum freeze-drying of multi-starch raw materials. In the production of vacuum freeze-dried foods, solidification of the food body by prior freezing is essential. Usually, rapid freezing is applied to freeze foods. Since it seems possible to convert the rapid freezing line (equipment) to a slow mode, the adoption of slow freezing may have less resistance. From such a consideration, it seems that the problem of water absorption and restoration during hot water pouring of freeze-dried cooked rice products has been solved by the adoption of slow freezing, but this is not always the case in actual production. For example, Patent Document 8 describes slow freezing at -3.5 °C for 24 hours, Patent Document 9 describes slow freezing at -8 °C for 8 hours, Patent Document 12 describes slow freezing at -1 to -4 °C for 5 hours or more and then transitioning to a general rapid freezing condition of -30 °C or lower after passing through -10 to -15 °C, and Patent Document 13 describes transitioning to rapid freezing at -30 °C or lower after slow freezing at -1 to -5 °C for 15 to 30 hours.

[0016] Generally, in the freezing of food materials and foods, slow freezing is avoided because it causes destruction of tissues or bodies due to the formation of large ice crystals, resulting in an increase in drip during thawing and deterioration of texture and appearance. Therefore, commercially available food freezers are designed to quickly pass through the temperature range of several degrees below zero to minus 10°C, which is called the so-called maximum ice crystal formation temperature zone (exactly the slow freezing condition). Temporary freezers for frozen food storage are designed to rapidly circulate cold air at minus 15 to 20°C, and freezing freezers are designed to increase the freezing rate by rapidly circulating cold air below minus 30°C. It is extremely difficult to modify a conventional freezer manufactured for rapid freezing to a specification that can achieve a slow cooling pattern with delicate temperature control over a long period of time, and there may be a need to newly install a dedicated freezer with a slow freezing specification.

[0017] Even after overcoming these difficulties and applying slow freezing, which has become common in the production of instant dried rice products, new problems remain. In general rapid freezing, the temperature difference between the ambient temperature inside the freezer and the product being frozen is large, so even if there are inconsistencies in the cooling temperature distribution and ambient circulation inside the freezer, the variation in the time it takes for the moisture in the product to be frozen (freezing, or immobilization of water molecules by ultra-low temperatures), which is distributed throughout the freezer, to reach a complete state is not so great. However, in slow freezing, due to the constraint that freezing must proceed slowly, the temperature difference between the ambient temperature and the product being frozen must not be large, and the circulation rate of cold air inside the freezer must also be slowed. In mass production, the product to be frozen must be distributed three-dimensionally and over a wide area inside the freezer, and it is easy to predict that there will be a large variation in the time it takes for freezing (or water immobilization) to reach a complete state due to differences in placement. In actual manufacturing, prepared rice products are filled into cups or trays with a capacity of about 100 to 200 milliliters, and the filled products are arranged in metal trays, each measuring about 1 meter square. These trays are then stored in racks with a vertical spacing of several centimeters to 5 centimeters, stacked in dozens of layers, and the racks are further packed tightly inside the storage area. In this state, the circulation of cold air is good at the edges of the rack stacks, resulting in rapid freezing. However, in the center of the stacks, the stacked racks and trays create resistance, slowing down the circulation of cold air and thus slowing down the freezing rate. To avoid large variations in the freezing completion rate, a continuous freezing method in which trays are passed through a steady-state cold air environment one by one by a driving mechanism would be ideal. However, passing through a cold air atmosphere for a long time, as seen in the slow freezing setting conditions of the aforementioned patent documents, would require a very long freezing line, which would be obviously impractical to those skilled in the art. When slow freezing is adopted for mass production, it can be easily inferred that variations in the water absorption and recovery properties of the dried product due to variations in the freezing rate are unavoidable. [Means for solving the problem]

[0018] In order to solve the above problems, the inventors diligently conducted repeated prototypes to realize a method for producing instant dried rice products using a commonly available rapid freezer under general conditions, without requiring a special freezer or multi-stage freezing temperature control for slow freezing, and established the manufacturing method described in the title.

[0019] The rapid freezer referred to here has a set temperature of -20°C or lower, and most of them are equipped with an atmosphere circulation mechanism called blasting to shorten the freezing time. Some equipment can achieve temperatures below -40°C, but most freezers are around -20°C to -30°C. The present invention can also be implemented in low-temperature equipment below -30°C.

[0020] One method of the present invention achieves the porosity of the inside of rice grains, which was previously achieved by conventional slow freezing, by adding carbonates or bicarbonates and by the expansion caused by the generation of carbon dioxide gas when the added salts are neutralized with acids. Specifically, as carbonates or bicarbonates, those permitted as additives under the Food Sanitation Law, such as baking soda, sodium carbonate, potassium carbonate, potassium bicarbonate, calcium carbonate, and calcium bicarbonate, are used. As acids, inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, and organic acids such as citric acid, malic acid, tartaric acid, fumaric acid, and gluconic acid are used.

[0021] In this invention, in order to avoid hindering water absorption due to the adhesion of stickiness to the surface of the rice grains when they are rehydrated with hot water after drying, the heating of the rice, i.e., the gelatinization of rice starch, is performed by steaming, which generates less stickiness, rather than by cooking, which generates a lot of stickiness. Steaming minimizes the leaching of starch from the rice, i.e., the generation of stickiness, which can occur when cooking. Steaming can be completed in about 15 to 40 minutes, depending on the amount of rice used. The stacked thickness of the rice grains should not exceed 10 centimeters, and the process should be carried out in a state where steam can sufficiently penetrate into the interior of the rice grain layer.

[0022] To further promote porosity, this invention involves immersing steamed rice in water or hot water to allow it to absorb water and swell. To avoid the formation of stickiness due to the progression of gelatinization on the surface of the rice grains, use an amount of water at room temperature or around 60°C that is sufficient to completely submerge the steamed rice until water absorption is complete. Generally, swelling due to water penetration into the rice grains accelerates as the water temperature rises, but sufficient water absorption is achieved in 1 to 2 hours. Immersion in 50°C hot water for 2 hours will increase the volume to three to three and a half times the original amount of rice (absorbing two to two and a half times the amount of water). In the first method, the aforementioned carbonate or bicarbonate is added to the immersion water. An addition concentration of about 0.1 to 0.5% relative to the water or hot water is sufficient. Excessive addition may lead to an off-flavor in the product. The amount of water to immerse the rice is about 5 to 10 times the amount of steamed rice, and the immersion time is about 30 to 120 minutes. After soaking, the cooked rice is drained in a colander to remove excess water and ensure that no excess carbonates or bicarbonates remain in the product. In the second method, steamed rice is soaked in additive-free water to allow it to absorb water and swell.

[0023] Next, the cooked rice is cooked into a porridge-like consistency. Generally, porridge refers to a food with a water content of 50% or more, meaning that the water content is four times the weight of the raw rice. However, to achieve rapid restoration when hot water is added to freeze-dried products, cooking with 80% porridge (7 times the amount of water to the raw rice) to 110% porridge (10 times the amount of water to the rice) is appropriate. Adding more water than this will result in a product that resembles gruel rather than porridge. When calculating the amount of water added during the cooking process, the water absorbed in the preceding water absorption process is subtracted, and the amount lost due to evaporation after cooking is replenished to arrive at the total amount of water added. Generally, a mild salty taste is preferred for porridge, so it is common practice to add about 0.2 to 0.5% salt to the total amount of rice during cooking.

[0024] In this method, the gelatinization of rice starch is completed by steaming, so cooking is usually completed within 5 to 20 minutes. If you observe the cooking process and see the rice grains beginning to dissolve, immediately stop heating and allow it to cool naturally. Otherwise, it will turn into a greasy consistency or the dried product will have reduced resilience due to excessive stickiness. As mentioned above, after cooking, add water to equalize the amount of evaporated water to keep the amount of water in the porridge constant. Again, it should be stated that cooking for too long is undesirable as it will cause the rice grains to break and the undesirable excessive stickiness to develop. Adding the aforementioned acids to the water during cooking allows the acids to penetrate into the rice grains, react with the carbonates and bicarbonates remaining inside the grains, and generate carbon dioxide, making the inside of the rice grains porous. As for the acid, inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, and organic acids such as acetic acid, lactic acid, malic acid, citric acid, tartaric acid, and gluconic acid can be used. However, it is sufficient to use an amount that does not produce sourness after rehydrating the dried product, specifically about 0.05 to 0.2% of the total amount of cooked rice.

[0025] The neutralization balance between baking soda and acid can be determined by chemical equivalent calculations, neutralization tests using small samples, visual observation during rice porridge cooking, or taste tests. The inventors observed that excessive alkalinity resulted in yellow discoloration of the rice grains, while excessive acidity resulted in a sour taste. The appropriateness of the added amount can also be determined by taste testing after the dried product has absorbed water and rehydrated.

[0026] The prepared rice product is allowed to cool slightly, and the specified amount is filled into containers. In most cases, one serving is filled into the containers, but if desired, it is also possible to fill larger containers and, after drying, cut into appropriate sizes or crush into appropriate granules and package them into single servings or the desired number of servings. In the case of filling, the filling thickness is generally around 20 to 30 mm as a compromise between the conflicting technical effects of minimizing the time required to complete freezing and vacuum freeze-drying, and preventing breakage during handling of the dried product. It should be noted that in vacuum freeze-drying, the shape of the product after drying is approximately the same as the shape of the raw material before drying (in the case of this invention, the shape and thickness after filling into containers).

[0027] Next, the rice product is frozen to a state where it can be vacuum freeze-dried, which, as mentioned above, can be done in a normal, general-purpose food freezer. Storing it in a freezer at -20°C to -30°C for several hours or even 20 hours will allow for complete freezing of the interior. The present invention can also be implemented in ultra-low temperature freezers below -40°C.

[0028] Thus, the completely frozen rice product is vacuum freeze-dried under general conditions. Here, "general" means a vacuum level of about 0.1 mmHg to 1 mmHg, a heating shelf temperature of 40 to 90°C, and a drying time of about 10 to 24 hours. The finished moisture content is about 4% or less, and the product is judged to be dry when it feels crisp to the touch, even inside. The freeze-drying apparatus is equipped with sensors to measure ambient pressure, shelf temperature, and product core temperature, and in a typical embodiment, drying is judged to be complete when the product core temperature and heating shelf temperature match after 2 to 3 hours. In addition, the shelf temperature is generally kept low at about 40 to 50°C for the first 30 minutes to 1 hour of drying, and after confirming that the drying process is stable, it is kept at a relatively high temperature of 70 to 90°C for several hours to 10 hours to maintain a constant drying state, and then the shelf temperature is lowered to about 40 to 60°C for several hours to dry in a decreasing drying state.

[0029] The second method of this invention also facilitates the restoration of dried products by promoting the expansion and internal porosity of steamed rice grains. In the previous method, baking soda was added to cause the steamed rice to expand by water absorption, but in the second method, additive-free water is absorbed, excess water is removed by filtration, and then porosity is achieved by normal freezing. "Normal" here refers to freezing at temperatures and in a well-ventilated atmosphere that are commonly used in food processing, including rapid freezing, not just slow freezing. As already mentioned, freezing creates ice crystals inside the rice grains, leading to porosity. The advantage of this method is that it can accommodate the recent trend among consumers to avoid the use of food additives in food processing. In the dried product of the previous method, it is necessary to list the names of baking soda and the acid used for neutralization on the packaging, but this is not necessary in this second method. Cooking porridge-like rice using this method can be completed in a shorter time than the former, within 10 minutes.

[0030] The preparation of steamed rice and immersion in water in this method are the same as in the previous method, except that no additives are used. The process of removing excess water, storing the water-absorbed and expanded steamed rice in a freezer until completely frozen, and then adding water and cooking it to make porridge is also the same as in the previous method, but naturally, the addition of acid is unnecessary. As long as the freezing conditions allow for freezing, there is no need to specialize any individual conditions such as the internal temperature or air circulation inside the freezer.

[0031] The frozen steamed rice thus obtained can be thawed, or placed in a cooking appliance while still frozen, and water can be added according to the previous method. After cooking, it can be cooled, filled into containers, pre-freezed, and freeze-dried to achieve the desired result. [Effects of the Invention]

[0032] Thus, the dried rice products prepared by the two methods of the present invention, when hot water at 90°C or higher is added, will absorb enough water within 3 minutes and be restored to a porridge or rice gruel consistency.

[0033] Furthermore, it goes without saying that the present invention can be applied to instant dried foods such as rice porridge or risotto, which can be appropriately seasoned with various seasonings such as salt, sucrose, monosodium glutamate, monosodium guanylate, monosodium inosinate, meat extracts, seafood extracts, vegetable extracts, tomato paste, ketchup, and spices, and optionally with ingredients such as meat, seafood, vegetables, mushrooms, tofu, and pickles.

[0034] This invention is applicable to the food processing field, particularly to the manufacture of instant dried rice products. [Modes for carrying out the invention]

[0035] The present invention will be specifically described below with reference to examples. Comparative examples will also be disclosed to clarify the technical effects of the present invention. [Examples]

[0036] 100g of Koshihikari rice from Hiroshima, with both the raw paddy and milled rice being less than six months old, was washed with tap water, drained in a colander for a few minutes, and then soaked in 500mL of 50-60°C water for one hour. It was then drained in a colander for 5 minutes. It was placed in a household steamer and steamed for 25 minutes at a boil, then removed and left at room temperature to cool. It was then soaked in 1L of 50-60°C tap water containing 0.2% baking soda for one hour. The swollen rice grains were drained in a colander for 5 minutes.

[0037] Rice grains were placed in a pot, and water was added until the total weight reached 1 kg (so that the amount of water added was 900 g for every 100 g of raw rice). 1 g of citric acid and 3 g of salt were added for seasoning. The pot was heated and kept to a gentle boil for 13 minutes before being removed from the stove. The pot was weighed, and the amount of water that had evaporated was replenished to make a total of 1 kg. It was then left to cool naturally for 10 minutes. 120 g of the prepared porridge was dispensed into commercially available containers (30 mm high, 53 mm in diameter of the circular base, 96 mm in diameter of the center circle of the circular top surface) made by shaping aluminum foil into a truncated cone, with the top edge folded into a rough star shape and the bottom folded to converge into a circle. These were placed on an aluminum tray and rapidly frozen in an air blast freezer at -25°C without a lid.

[0038] After 10 hours, the individual containers were transferred to a test freeze-dryer and freeze-dried on a heating shelf under an atmosphere of reduced pressure of approximately 0.3 mmHg. The first stage of shelf heating was performed as follows: 1 hour without heating, 4 hours at 80°C, 6 hours at 60°C, and 5 hours at 50°C. Approximately 2 hours before confirmation of drying completion, the product temperature sensor reading dropped to approximately 50°C and remained stable thereafter.

[0039] When the dried product was removed and weighed, it ranged from 9.2g to 9.6g. Visually, the gaps between the puffed rice grains were filled with a colorless, porous, fibrous, crisp, sticky dried material, and the dried product did not break with normal handling. The moisture content was approximately 3%. When this was placed in a bowl and 180mL of hot water (over 90°C) was poured over it and gently stirred with chopsticks, it absorbed the water and rehydrated into porridge in 1 minute. [Examples]

[0040] Similar results were obtained in Example 1 by substituting rice with Akita Komachi rice from Okayama Prefecture. [Examples]

[0041] In Example 1, the rice was changed to Niigata-grown Milky Queen, and the baking soda was changed to 0.3%, citric acid to 1.5g, and salt to 4g to obtain a similar dried product. [Examples]

[0042] In Example 1, 2g of commercially available dried chicken consommé was added to porridge that had been cooked and adjusted to a weight of 1kg by adding water. Separately, 10g of minced chicken, lightly stir-fried and simmered with appropriate amounts of salt, pepper, sage, nutmeg, and soy sauce, was added, along with 1g of chopped parsley that had been blanched in boiling water for 1 minute, cooled under running water, and drained in a colander, for color and flavor. The mixture was then gently stirred to make it uniform, filled into a container, rapidly frozen, and vacuum freeze-dried to produce an instant dried food product resembling chicken risotto. [Examples]

[0043] Steamed rice was prepared according to Example 1 and immersed in 1 liter of tap water at 50 to 60°C for 1 hour. The swollen rice grains were placed in a colander and left to drain for 5 minutes. After water absorption, the weight of the steamed rice was 330 g. This was filled into a plastic bag and frozen in an air blast freezer at -25°C for 24 hours. The rice was removed from the plastic bag, placed in a pot, and water was added to make a total volume of 1 kg. 2 g of salt was added, and the rice was cooked over low heat until completely thawed. After thawing, it was cooked for 8 minutes in the same manner as in Example 1 (however, no acid was added), water was added, it was allowed to cool, filled into containers, pre-frozen, and freeze-dried to obtain a similar dried rice product. This product also exhibited the same hot water absorption and recovery properties as the dried product of Example 1. [Examples]

[0044] 200g of Koshihikari rice was washed and drained in a colander. It was soaked in 700mL of warm water (40-50℃) for one hour, then drained in a colander to obtain 280g of soaked rice. This was steamed for 20 minutes and then allowed to cool to obtain 310g of cooked rice. This was soaked in 700mL of warm water for one hour, then drained in a colander to obtain 650g of cooked rice. This was then divided into two portions.

[0045] 300g of soaked cooked rice was placed in a plastic bag and frozen overnight in an air blast freezer at -35°C. This was then left at room temperature in the plastic bag to partially thaw. This partially thawed product contained 92g of rice and 208g of water. This was then placed in a pot, 700mL of water was added, and it was gently simmered for 10 minutes to make porridge. Evaporated water was replenished. Calculations show that this porridge contained 92g of rice and 908g of water, equivalent to what is commonly known as eleven-part porridge. 100g of this was measured into aluminum cups and frozen overnight in an air blast freezer at -25°C. This was then dried using a standard freeze-drying method (initial shelf temperature 60°C, maximum shelf temperature 80°C, final shelf temperature 60°C, drying time 22 hours) until it became crisp. This was then placed in a cup, and 180mL of boiling water (within one minute of boiling) was poured over it, restoring it to porridge within two minutes.

[0046] The remaining 300g of the aforementioned soaked rice was placed in a plastic bag and frozen overnight in an air blast freezer at -25°C. This was then left at room temperature in the plastic bag to partially thaw. This partially thawed product contained 108g of rice and 242g of water. This was then placed in a pot, 550mL of water and 3g of salt were added, and it was gently simmered for 10 minutes to make porridge. Evaporated water was replenished. Calculations show that this porridge contained 108g of rice and 792g of water, equivalent to what is commonly known as "eight-tenths porridge." 100g portions of this were measured into aluminum cups and frozen overnight in an air blast freezer at -25°C. These were then dried using a standard freeze-drying method (initial shelf temperature 60°C, maximum shelf temperature 80°C, final shelf temperature 60°C, drying time 22 hours) until crisp. When this was placed in a cup and 180 mL of boiling water (within one minute of boiling time) was poured over it, it reconstituted into porridge within two minutes. (Control example 1)

[0047] 100g of washed and drained Koshihikari rice was added to 900g of water and gently boiled for 25 minutes to make porridge. After replenishing the amount of water equivalent to the evaporated water, it was dispensed according to Example 1, rapidly frozen, and vacuum freeze-dried. 180mL of hot water was poured over the dried product and gently stirred with chopsticks, but water absorption did not resume even after 3 minutes. Control Example 2

[0048] 100g of Koshihikari rice was washed and steamed in the same manner as in Example 1 to make steamed rice. This was then soaked in water to swell (increasing the weight to 3.3 times the original weight of the rice). After draining the water, water was added to the pot so that the total weight of the contents was 10 times that of the rice, and then boiled, with water added to compensate for the loss due to evaporation. The mixture was dispensed into thin aluminum containers, rapidly frozen, and then vacuum freeze-dried. 180mL of hot water was poured over the dried product and gently stirred with chopsticks, but even after 3 minutes, water absorption did not resume.

Claims

1. A method for manufacturing instant rice products, characterized in that, in order to improve the hot water absorption and regeneration properties of the dried product, the inside of the rice grains is made porous after the steamed rice has absorbed water.

2. A method for producing an instant rice product according to claim 1, characterized in that the inside of the rice grains is made porous by adding alkaline salts selected from carbonates or bicarbonates to the water in which the steamed rice is soaked, and by adding an acid to the water used for cooking the rice, thereby generating carbon dioxide through the neutralization of the alkaline salts and salts during cooking.

3. A method for producing instant rice products according to claims 2 and 3, characterized in that baking soda is selected as the alkali salt and citric acid as the acid.

4. A method for producing an instant rice product according to claim 1, characterized in that the rice grains are made porous by freezing rice that has been soaked in water to allow it to absorb water.