Producing method of cocked rice

Abstract

To provide a producing method of frozen cooked rice difficult to cause quality deterioration due to thawing and chilled storage thereafter.SOLUTION: A method for producing cooked rice that includes: a soaking step in which the raw rice is immersed in water at 10 to 35°C to absorb water; a heating and pressurizing step in which the rice after the soaking process is steamed with saturated steam under a pressure of 130 to 200 kPa; a water absorption step in which water not exceeding 60°C is added to the rice after the heating and pressurizing process to allow absorption; and a freezing step in which the rice after the water absorption process is frozen.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing cooked rice, which includes a freezing step.

[0002] In recent years, with the diversification of eating occasions, the trend toward individual meals, and the increasing trend toward convenience, there has been an increasing demand for cooked rice products distributed in a frozen and / or chilled state as merchandise for the food service industry, supermarkets, convenience stores, department store basements, or the ready-meal industry via delivery, etc. For example, there are distribution formats in which cooked rice is frozen, thawed, and chilled, such as being delivered frozen to retailers or bento businesses and sold thawed. In this case, the cooked rice is eaten after being frozen and then thawed and chilled.

[0003] It is known that cooked rice undergoes significant aging when stored at low temperatures, particularly when frozen, thawed, or chilled. In general, cooked rice loses its viscosity and hardens when stored at low temperatures, resulting in a significant deterioration in texture. When frozen or thawed, when the rice passes through the maximum ice crystal formation temperature range of -5°C to -1°C, the moisture retained in the tissue is taken away by the growth and sublimation of ice crystals, which makes aging more likely to progress. In addition, when the rice passes through the chilled temperature range (0 to 10°C), where aging is likely to progress, aging progresses and the viscosity decreases and hardening easily occurs. In particular, when the rice is left in the chilled temperature range or at room temperature for natural thawing, aging is likely to occur because the time spent in the maximum ice crystal formation temperature range and the chilled temperature range is long. Ripe cooked rice can be restored to a certain degree of viscosity and softness by reheating it when eaten. However, there is a need for products that can be eaten without reheating, and in this case, suppressing aging becomes an even more important issue. Regarding the prevention of deterioration of cooked rice stored at low temperatures, Patent Document 1 proposes a method of solving the problem by combining the use of a gelling agent and the amount of water added for cooking the rice.

[0004] As documents that do not mention frozen storage, Patent Documents 2 and 3 describe methods for producing cooked rice that combine water absorption and heating. Patent Document 4 describes a method for producing cooked rice, which involves soaking, steaming, cooling, absorbing water, and freezing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-118760 A [Patent Document 2] JP 2008-000086 A [Patent Document 3] JP 2006-174780 A [Patent Document 4] Japanese Patent Application Publication No. 11-155505 Summary of the Invention [Problem to be solved by the invention]

[0006] Generally, staling is easily prevented by adding a lot of moisture to rice. On the other hand, in order to add a lot of moisture to rice, it is necessary to heat it. However, when a lot of moisture is added and the rice is heated, starch is easily eluted from the rice grains, which makes the rice grains lose their shape and results in a poor appearance. For these reasons, it is particularly difficult to achieve both grain shape and staling prevention under low-temperature storage conditions that are conducive to staling. Patent Document 1 describes that cooked rice for low-temperature storage obtained by the method described therein has excellent resistance to aging. However, in recent years, demand for cooked rice, which is stored at low temperatures, particularly through a process of freezing, thawing and chilled storage, has been diversifying, and new technologies for inhibiting aging are required. Furthermore, the inventors have found that the methods described in Patent Documents 2 to 4 are not sufficient in terms of suppressing deterioration in quality due to low-temperature storage. An object of the present invention is to solve the above-mentioned problems and to provide a method for producing frozen cooked rice that is less susceptible to deterioration in quality due to thawing and subsequent refrigerated storage. [Means for solving the problem]

[0007] After extensive research, the inventors have discovered that by producing frozen rice by carrying out a soaking step at a predetermined temperature, a heating and pressurizing step at a predetermined pressure, and a water absorption step at a predetermined temperature in that order, it is possible to suppress the deterioration of quality that occurs during thawing and chilled storage while preventing deterioration of the grain shape.

[0008] The present invention is based on the above findings, and comprises a soaking step of soaking rice as a raw material in water at 10 to 35°C to absorb water; a heating and pressurizing step of steaming the rice after the soaking step with saturated steam under a pressure of 130 to 200 kPa; A water absorption process in which water not exceeding 60°C is added to the rice after the heating and pressurizing process and absorbed; and a freezing step of freezing the rice after the water absorption step.

[0009] The present invention also provides cooked rice produced by the above method. Effect of the Invention

[0010] According to the present invention, there is provided a method for producing frozen cooked rice that is resistant to deterioration in quality due to thawing and subsequent refrigerated storage, and cooked rice obtained using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will now be described based on preferred embodiments thereof.

[0012] The present invention relates to cooked rice and a method for producing cooked rice. The present invention includes a soaking step, a heating and pressurizing step, a water absorption step, and a freezing step. First, a first preferred embodiment of the present invention will be described.

[0013] <Soaking process> In the soaking step, the raw material rice is soaked in water at 10 to 35° C. to allow the rice grains to absorb the water. The raw rice may be glutinous rice, non-glutinous rice, or a combination of these. In the case of non-glutinous rice, low amylose rice is preferable in terms of resistance to aging. Low amylose rice refers to rice with a low amylose content, and refers to rice with an amylose content of less than 17%. Specific examples of rice included in the category of low amylose rice in the present invention include many varieties such as "Hanabusa", "Irodori", "Takitate", "Silky Pearl", "Snow Pearl", "Milky Queen", "Hokuriku 180", "Soft 158", "Yuru Komachi", "Asa Tsuyu", "Nebari Kachi", "Iwata 15", "Ou 344", "Nishikai 215", "Milky Summer", and "Yumepirika". As the raw rice, one of these may be used alone as raw rice, or two or more may be used in combination. The degree of polishing of raw rice is not particularly limited, and may be any of brown rice, partially polished rice, and white rice. Raw rice may be, for example, rice that has not been heated at 60° C. or higher for 30 seconds or more.

[0014] The moisture content of the rice after the soaking treatment is preferably 36 to 45% by mass. By soaking the rice until the moisture content is 36% by mass or more, it becomes easier to gelatinize the rice to the center during the heating and pressurizing process described below, and it becomes easier to obtain a sticky texture and to suppress hardening even after the freezing, thawing and chilling processes. Furthermore, by making the moisture content 45% by mass or less, it becomes easier to obtain a good grain shape. From these viewpoints, it is even more preferable that the moisture content of the rice after the soaking treatment is 36 to 44% by mass. In particular, when the rice is glutinous rice, the moisture content of the rice after the soaking treatment is preferably 39 to 45% by mass, and more preferably 40 to 44% by mass. Furthermore, when the rice is non-glutinous rice, the moisture content of the rice after the soaking treatment is preferably 36 to 45% by mass, and more preferably 37 to 44% by mass. In addition, when the raw material rice is glutinous rice, this includes cases where the proportion of glutinous rice in the raw material rice used is more than 50% by mass, and more preferably 60% by mass or more, and when the raw material rice is non-glutinous rice, this includes cases where the proportion of non-glutinous rice in the raw material rice used is more than 50% by mass, and more preferably 60% by mass or more. In the present invention, the "moisture content (%)" of rice or cooked rice refers to the amount of moisture (g / 100 g) that is determined by weighing approximately 3 g of rice or cooked rice into a weighing can (a weighing can with an inner diameter of 55 mm at the mouth, an inner diameter of 50 mm at the bottom, and a depth of 25 mm, which has been used to determine a constant weight) and drying this at 135°C for 3 hours.

[0015] The soaking treatment in the soaking step is carried out by soaking rice in water. In order to allow the rice grains to sufficiently absorb water, it is necessary to adjust the temperature and time when soaking the rice in water. The specific conditions can be set by those skilled in the art, but since a low water temperature slows down the rate of penetration into the rice grains, the soaking treatment is preferably carried out under conditions where the water temperature is 10 to 35°C, and more preferably under conditions where the water temperature is 15 to 30°C. In order to allow the rice grains to sufficiently absorb water, the rice is preferably soaked in water of the above temperature range for about 10 to 300 minutes, and more preferably for about 30 to 180 minutes.

[0016] <Heat and pressure process> In the next heating and pressurizing step, the rice after the soaking step is steamed with saturated steam under a pressure of 130 to 200 kPa. This step is a steaming step. Steaming is a method of heating rice by directly contacting steam with an object to be heated, and in this respect, it differs from the boiling or cooking step in which rice is heated while soaked in water. For example, in the cooking step, the rice obtained is soft overall and has a sticky surface, and is particularly sticky when the moisture content is high. On the other hand, in the steaming step, the stickiness of the surface can be suppressed to a certain extent even if the inside is softened. As described above, since this step is a steaming step, if the rice is in a soaked state with a lot of water remaining around it after the soaking step, the water used for soaking is drained to remove the water used for soaking, and then the rice is subjected to the heating and pressurizing step.

[0017] In this process, it is important that the pressurization process is performed to facilitate gelatinization to the center of the rice grain. In contrast, Patent Documents 2 and 3 state that it is desirable not to gelatinize the rice grains in the heating process after soaking (claim 1 of Patent Document 2, paragraph

[0023] of Patent Document 3), and these descriptions discourage the use of a heating and pressurizing process. In the present invention, it is important that the pressurization condition is 130 to 200 kPa. If the pressure is less than 130 kPa, gelatinization does not progress to the center of the rice grain, and after the freezing, thawing, and chilling processes, the rice may have a hard texture with a remaining core. In addition, if the pressure exceeds 200 kPa, the grains may lose their granular texture and become too soft. From these viewpoints, the pressure in the heating and pressurizing process is more preferably 140 to 190 kPa.

[0018] The temperature of the steam in the heating and pressurizing step is preferably 101° C. to less than 125° C., more preferably 101° C. to 123° C., even more preferably 101° C. to 120° C., and particularly preferably 105° C. to 115° C. When the temperature of the steam is 101° C. or higher, gelatinization is facilitated, and the rice is easily prevented from becoming hard even after the freezing, thawing, and chilling steps. When the temperature of the steam is less than 125° C., the possibility of damaging the shape of the rice or causing overheating of the rice due to an excessively high heating temperature can be prevented, and good graininess can be achieved.

[0019] The moisture content of the rice after the heating and pressurizing step is preferably 38 to 50% by mass, more preferably 39 to 48% by mass, from the viewpoints of graininess, appropriate stickiness, prevention of dryness and stickiness, and control of hardness. In particular, when the rice is glutinous rice, the moisture content of the rice after the heating and pressurizing step is preferably 40 to 50% by mass, and more preferably 43 to 48% by mass. Furthermore, when the rice is non-glutinous rice, the moisture content of the rice after the heating and pressurizing step is preferably 38 to 49% by mass, and more preferably 39 to 48% by mass. From the same viewpoint, the heating and pressing time is preferably 1 to 180 minutes, more preferably 5 to 120 minutes, and even more preferably 10 to 60 minutes, where the heating and pressing time refers to the time during which heating is performed at a pressure in the range of 130 to 200 kPa.

[0020] <Water absorption process> In this water absorption process, water not exceeding 60°C is added to the rice after the heating and pressurizing process and is absorbed.

[0021] In the water absorption step, the moisture content of the rice is preferably adjusted to 57 to 75% by mass. If the moisture content of the rice is 57% by mass or more, it is preferable because it is easy to increase the resistance to aging when frozen, thawed, and then stored in a chilled state. If the moisture content is 75% by mass or less, it is preferable because it is possible to prevent the cooked rice from having a sticky and undesirable texture due to a high moisture content. From these viewpoints, the moisture content of the rice is more preferably adjusted to 60 to 70% by mass. In addition, as in the second embodiment described below, when the method for producing cooked rice of the present invention includes multiple water absorption steps before the freezing step, "adjusting the moisture content of the rice to 57 to 75% by mass in the water absorption step" includes adjusting the moisture content of the rice to 57 to 75% by mass in the final water absorption step (for example, the second water absorption step described below) among the multiple water absorption steps. In this case, for example, the amount described below is an example of a preferable moisture content to be adjusted in the first water absorption step.

[0022] The temperature of the water absorbed by the rice in the water absorption step is 60°C or lower, which has the advantage that, unlike rice cooking, water can be added while preventing the rice from expanding and losing its grain shape. The temperature of the water is preferably 5°C or higher, since this makes it easier to adjust the moisture content of the rice after the water absorption step to the above range, and more preferably 10 to 35°C.

[0023] The moisture content in the water absorption step can be controlled by the amount of water added and the water absorption time. When controlling by the water addition time, for example, the rice after the heating and pressurizing step is soaked in a large amount of water for a certain period of time. After soaking, if the rice is soaked in a large amount of water and a large amount of water adheres to the surface, it is preferable to remove the adhered water before the next freezing step. The water can be removed, for example, by placing the rice removed from the soaking water on a sieve and leaving it there, or by shaking the sieve to drain the water. Even when controlling by the amount of water added, the rice after the heating and pressurizing step can be made to absorb water by contacting it with water by a method such as soaking.

[0024] In the water absorption step, in order to successfully obtain rice having the above moisture content, it is preferable to add 10 to 300 parts by mass of water, and more preferably 20 to 200 parts by mass of water, per 100 parts by mass of rice after the heating and pressurizing step. In order to successfully obtain rice having the above moisture content, the time for contacting the rice with water and allowing it to absorb water is preferably 1 to 600 seconds, and more preferably 30 to 300 seconds.

[0025] In the water absorption step, additives such as food materials and food additives may be contained in the rice grains within a range that does not impair the effects of the present invention. Examples of the additives include salts such as salt; monosaccharides such as glucose, disaccharides such as sucrose and trehalose, oligosaccharides of three or more sugars, and sugar alcohols; sweeteners; seasonings such as vinegar, soy sauce, miso, dashi, consomme, sodium glutamate, ketchup, curry powder, and saffron; enzymes such as amylase and transglutaminase; fats and oils such as salad oil, soybean oil, rapeseed oil, corn oil, sesame oil, and butter; antioxidants such as vitamin E; colorings, flavorings, preservatives, shelf life improvers, and the like, and these may be used alone or in combination of two or more. By mixing such additives with water and allowing them to absorb water, they can be contained in the rice grains.

[0026] In the first embodiment, the heating and pressurizing step and the water absorption step are preferably carried out continuously. "Continuously" means that the rice removed from the heater in the heating and pressurizing step is brought into contact with water at a temperature not exceeding 60° C. For example, it is preferable to bring the rice into contact with the water at a temperature of 60° C. or higher.

[0027] <Freezing process> In this process, the cooked rice obtained in the water absorption process is frozen. The freezing method is not particularly limited, and can be performed using a mechanical freezing device or a freezing device using dry ice, etc. For example, fried rice can be frozen in pieces by performing a freezing process in which the rice is loosened and stirred. The freezing step is preferably rapid freezing. Rapid freezing is defined as the time it takes for the rice to pass through the maximum ice crystal formation temperature range of -1°C to -5°C (T -1℃~-5℃ ) for 30 minutes or less. After the water absorption step, the cooked rice is preferably packaged and frozen, since this can avoid thawing and the resulting deterioration that accompanies the packaging step, as compared to packaging after freezing.

[0028] The method for producing cooked rice of the present invention may include a step of cooling the cooked rice obtained after the water absorption step and before the freezing step. The cooling method of the cooked rice in the cooling step is not particularly limited, and examples thereof include cooling by loosening the cooked rice with a rice scoop, cooling under differential pressure, vacuum cooling, or a combination thereof.

[0029] Next, a second preferred embodiment of the present invention will be described. The second embodiment includes a second heating step in which the raw rice after the water absorption step is subjected to a heat treatment of steaming, instead of the first embodiment in which the rice is frozen without being heated after the water absorption step; and a second water absorption step of adding water not exceeding 60°C to the raw material rice after the second heating step to allow the raw material rice to absorb the water, and the cooked rice obtained in the second water absorption step is subjected to the freezing step. In the case of this second embodiment, by going through the second steaming step and the subsequent water absorption step, the cooked rice obtained has particularly sufficient gelatinization of the inside of the rice grains, and after freezing and thawing, the cooked rice has particularly excellent moderate stickiness and moderate hardness when stored in a refrigerated state. The following mainly focuses on the differences from the first embodiment. In this embodiment, the explanation of the first embodiment applies as appropriate to the points other than those described below.

[0030] In the case of the second embodiment, the moisture content of the rice after the heating and pressurizing step is preferably adjusted to 38 to 50% by mass, and more preferably adjusted to 39 to 48% by mass. In particular, when the rice is glutinous rice, the moisture content of the rice after the heating and pressurizing step is preferably adjusted to 40 to 50% by mass, and more preferably adjusted to 42 to 48% by mass. Furthermore, when the rice is non-glutinous rice, the moisture content of the rice after the heating and pressurizing step is preferably adjusted to 38 to 50% by mass, and more preferably adjusted to 39 to 48% by mass. When the moisture content of the rice is within this range, the moisture content of the rice after the next water absorption step (first water absorption step) and the second heating step and second water absorption step can be made appropriate, and the rice can have a good shape as well as have a high resistance to aging when thawed and stored in a chilled state. In this case, the heating and pressurizing time is preferably 1 to 180 minutes, more preferably 5 to 120 minutes, and even more preferably 10 to 60 minutes.

[0031] In this embodiment, the moisture content of the rice after the water absorption step is preferably 40% by mass or more, more preferably 42% by mass or more, and even more preferably 45% by mass or more. In addition, the moisture content of the rice after the water absorption step is preferably 57% by mass or less, more preferably 56% by mass or less, and even more preferably 55% by mass or less. If the moisture content of the rice in the water absorption step is the above upper limit or less and / or the above lower limit or more, it is easy to make the moisture content appropriate after the subsequent second heating step and second water absorption step, and it is easy to further increase the aging resistance when refrigerated after thawing, and it is easy to make the shape of the rice good. Each upper limit and lower limit can be used in combination without limitation (same below).

[0032] <Second heating process> In the second heating step, the rice after the water absorption step is steamed to further gelatinize it. This heating step may be a pressurizing step, but is preferably carried out under normal pressure (atmospheric pressure). By carrying out the first heating step as a heating and pressurizing step and the second heating step under normal pressure, it is possible to produce rice grains that have a good grain shape while having appropriate stickiness and hardness.

[0033] The temperature of the water vapor in the second heating step is preferably 80 to 120°C. If the temperature of the water vapor is 80°C or higher, gelatinization proceeds sufficiently, the water absorption into the cooked rice becomes sufficient, and the texture of the cooked rice after cold thawing becomes more preferable. If the temperature is 120°C or lower, the possibility of the surface of the rice drying out or the rice being overheated can be prevented. From these viewpoints, the temperature of the water vapor is more preferably 85 to 110°C. The water vapor in the second heating step is preferably saturated water vapor.

[0034] The moisture content of the rice after the second heating step is preferably 43% by mass or more, more preferably 46% by mass or more, even more preferably 48% by mass or more, and particularly preferably 50% by mass or more. After the water absorption step, the moisture content of the rice is preferably 60% by mass or less, more preferably 58% by mass or less, and even more preferably 57% by mass or less. By being above the above lower limit, the core of the rice is less likely to remain, the cooked rice is moderately hard, and the texture of the cooked rice can be prevented from becoming dry. By being below the above lower limit, the texture of the cooked rice obtained can be made less sticky and more preferable.

[0035] For the same reasons as above, the heating time in the second heating step is preferably from 5 to 120 minutes, more preferably from 10 to 60 minutes.

[0036] <Second water absorption process> In the second water absorption step, the rice after the second heating step is subjected to a water absorption treatment to further absorb water. In this second water absorption step, the water content of the cooked rice (rice) is preferably adjusted to 57 to 75% by mass, more preferably adjusted to 60 to 70% by mass, and even more preferably adjusted to 62 to 68% by mass. If the water content of the rice after the second water absorption step and before the freezing step is equal to or higher than the above lower limit, this is preferred because it is easier to further improve the resistance to aging when frozen, thawed, and then stored in a chilled state. If the water content of the rice is equal to or lower than the above upper limit, this is preferred because it further improves the prevention of stickiness in the texture of the cooked rice obtained.

[0037] The temperature of the water used in the second water absorption step is 60°C or lower, which has the advantage that, unlike rice cooking, water can be added while preventing the rice from expanding and losing its grain shape. The temperature of the water is preferably 5°C or higher, since this makes it easier to adjust the moisture content of the rice after the second water absorption step to the above range, and is more preferably 10 to 35°C.

[0038] In the second water absorption step, in order to successfully obtain rice having the above moisture content, it is preferable to add 10 to 40 parts by mass of water, and more preferably 15 to 35 parts by mass of water, per 100 parts by mass of rice after the second heating step. In order to successfully obtain rice having the above moisture content, the contact time with water is preferably 1 to 600 seconds, and more preferably 30 to 300 seconds.

[0039] As for the explanation of the second water absorption step and the subsequent steps, the explanation of the water absorption step of the first embodiment can be adopted without any particular limitation.

[0040] The cooked rice of the present invention is obtained by the above steps. The present invention also provides cooked rice obtained by the above production method. The cooked rice of the present invention is preferably cooked rice for low-temperature storage. "For low-temperature storage" refers to cooked rice that is distributed and sold in a low-temperature stored state and can be eaten without reheating. "Low-temperature storage" refers to storage at a temperature range of 10°C or less, and includes chilled storage and frozen storage, and in the case of frozen foods, also includes the processes of freezing and thawing. "Chilled storage" refers to storage in a chilled temperature range, and "frozen storage" refers to storage in a freezing temperature range.

[0041] Examples of cooked rice for low-temperature storage include frozen cooked rice stored in a freezing temperature range and chilled cooked rice stored in a chilled temperature range, with frozen cooked rice being preferred. Frozen cooked rice includes frozen chilled cooked rice stored in a chilled temperature range after being stored in a freezing temperature range. The freezing temperature range refers to a temperature range below the freezing start temperature, for example, below -18°C. The chilled temperature range refers to a temperature range below 10°C until the freezing starts. Cooked rice for low-temperature storage can be eaten as it is after naturally thawing frozen cooked rice, that is, thawed at room temperature or a chilled temperature range, and chilled cooked rice that has been chilled from production to distribution and end consumption can be eaten as it is. Here, naturally thawing refers to a method of thawing a frozen product by leaving it in a temperature environment where thawing is possible, such as room temperature or a refrigerator, without performing a heating operation such as microwave heating.

[0042] The present invention is not limited to white rice, but can be applied to various cooked rice such as takikomi gohan (rice cooked with seasonings), okowa (sticky rice), chimaki (rice dumplings), ohagi (rice balls), porridge, red rice, dry curry, and risotto. In this case, the seasoning ingredients required for seasoning can be added appropriately in the water absorption process or the second water absorption process, as described above. In addition to these processes, a seasoning process may be added. Also, a rice washing process may or may not be added as the first process, and pre-washed rice may be used.

[0043] By adopting the above-mentioned manufacturing method, the present invention makes it difficult for quality deterioration to occur. An example of a case where quality deterioration is unlikely to occur is when the rice grains have both a good shape and a good texture. A good shape of rice grains means that the rice grains are uniform in shape with little crushing, chipping, or deformation, in other words, have good "graininess." A good texture means that the rice has appropriate stickiness and hardness. An example of a case where quality deterioration is unlikely to occur is when the aging inhibition effect is high compared to when a different manufacturing method is used. The present invention also provides cooked rice obtained by the above-mentioned manufacturing method. It takes an extremely long time to specify the composition of this cooked rice as a product that can be defined as cooked rice obtained by the manufacturing method of the prior art, and there are circumstances in which it is substantially impossible or impractical under the request for early examination under the first-to-file system. For this reason, in this application, cooked rice as a product is defined by the manufacturing method. EXAMPLES

[0044] Hereinafter, unless otherwise specified, parts and % refer to "parts by mass" and "% by mass", respectively.

[0045] 1. Frozen rice production 1 (glutinous rice) Example 1 (1) Soaking process Polished glutinous rice (variety: Hakucho Mochi) was used as the raw material rice. 100 parts of glutinous rice was soaked in 300 parts of water at room temperature (25°C) for 2 hours. After that, it was placed on a sieve to drain the water. The moisture content of the rice was 43%.

[0046] (2) Heat and pressure process After the soaking process, the raw rice was placed in a heating and pressurizing device and pressurized and heated with saturated steam at 170 kPa and 115°C for 15 minutes.

[0047] (3) Water absorption process After the heating and pressurizing process, 26 parts of water at 25°C was added to 100 parts of rice at 90°C and mixed thoroughly for 1 minute to allow the rice to absorb water. The moisture content of the rice was as shown in Table 1.

[0048] (4) Second heating step 100 parts of rice after the water absorption process was placed in a steamer and heated for 10 minutes with saturated steam at 100°C under normal pressure.

[0049] (5)Second water absorption process After the second heating step, 100 parts of 90°C rice was mixed with 20 parts of 25°C water and mixed thoroughly for 1 minute to allow the rice to absorb water. The moisture content of the rice was as shown in Table 1.

[0050] (6) The obtained rice was cooled to 20°C in a vacuum cooling machine (Miura Co., Ltd.) immediately after production, then placed in a container and sealed, and frozen with cold air at -40°C in a quick freezer (Hoshizaki Co., Ltd.) to obtain the frozen rice of Example 1.

[0051] (Examples 2 to 3, Comparative Example 1) In Example 1, the pressure in the heating and pressurizing step was changed to the value shown in Table 1. Other than that, frozen cooked rice was obtained in the same manner as in Example 1.

[0052] Example 4 In the second heating step of Example 1, instead of steaming the rice at normal pressure, a heating and pressurizing device was used to heat and pressurize the rice at 170 kPa and 115° C. for 10 minutes. Except for this, frozen cooked rice was obtained in the same manner as in Example 1.

[0053] Comparative Example 2 In the heating and pressurizing step of Example 1, instead of heating 100 parts of rice after the water absorption step while pressurizing it, it was placed in a steamer and heated for 15 minutes with saturated steam at 100°C under normal pressure. Except for that, frozen cooked rice was obtained in the same manner as in Example 1.

[0054] Example 5 After the heating and pressurizing step, 56 parts of water at 25°C was added to 100 parts of rice at 90°C and mixed thoroughly for 1 minute to allow the rice to absorb water. The moisture content of the rice was as shown in Table 1. The rice was immersed in water continuously from the heating and pressurizing step. Thereafter, the rice was cooled, packaged and frozen in the same manner as in (6) of Example 1 without carrying out the second heating step and the second water absorption step, to obtain frozen cooked rice.

[0055] Example 6 The heating and pressurizing step was carried out for 20 minutes. Except for this, frozen cooked rice was obtained in the same manner as in Example 5.

[0056] Comparative Example 3 This comparative example corresponds to the invention described in Patent Document 2 (JP Patent Publication No. 2008-000086). The (4) steaming step in this example corresponds to the "rice cooking step" in Patent Document 2, in which rice is heated in a state in which "there is no aqueous phase around the rice" (the same applies to Comparative Example 5). (1) Soaking process Polished glutinous rice (variety: Hakuchomochi) was soaked in water at 5°C for 15 minutes as the raw material rice, and then placed on a sieve to drain the water, obtaining rice with a moisture content of 25%. (2)Heating process After the soaking process, the rice was heat-treated using saturated steam at 100°C for 2 minutes at normal pressure. (3) Water absorption process After the heating process, water (25°C) was added to the rice in an amount such that the moisture content of the rice was 59%, and the rice was kept for 60 minutes to allow it to absorb the water, resulting in rice with a moisture content of 59%. (4) Steaming process The rice after the second water absorption step was placed in a container and steamed at normal pressure for 10 minutes. The resulting rice was cooled, packaged and frozen in the same manner as in Example 1(6) to obtain frozen cooked rice.

[0057] Comparative Example 4 In Comparative Example 3, (4) in the steaming step, instead of normal pressure heating, the rice was placed in a pressurized heating device and heated under pressure (170 kPa) with saturated steam at 115° C. In the other respects, frozen cooked rice was obtained in the same manner as in Comparative Example 3.

[0058] Comparative Example 5 This comparative example corresponds to the invention described in Patent Document 3 (JP-A-2006-174780). (1) First water absorption process Polished glutinous rice (variety: Hakuchomochi) was soaked in water at 25°C for 120 minutes as the raw material rice, and then placed on a sieve to drain the water, yielding rice with a moisture content of 39%.

[0059] (2)Heating process After the first water absorption process, the rice was heat-treated using saturated steam at 100°C for 60 minutes at normal pressure.

[0060] (3) Water absorption process After the heating process, water (25°C) was added to the rice so that the moisture content of the glutinous rice was 60%, and the rice was held for 60 minutes to allow it to absorb the water, resulting in rice with a moisture content of 60%.

[0061] (4) Steaming process The rice after the second water absorption step was placed in a container and steamed at normal pressure for 10 minutes. The resulting rice was cooled, packaged, and frozen in the same manner as in Example 1(6).

[0062] Comparative Example 6 In Comparative Example 5, (4) in the steaming step, instead of heating under normal pressure, the rice was placed in a pressurized heating device and heated under pressure (170 kPa) with saturated steam at 115° C. In the other respects, frozen cooked rice was obtained in the same manner as in Comparative Example 5.

[0063] 2. Thawing of frozen cooked rice and evaluation after thawing 1 The frozen cooked rice produced in each Example and Comparative Example was stored in a freezer (-18°C) for 2 weeks, then transferred to a refrigerator at 7°C and stored at 10°C for 72 hours. It was then left to stand at room temperature (25°C) for 10 minutes.

[0064] After leaving the samples, eight expert panelists tasted the samples and evaluated their appearance (graininess) and texture (stickiness and hardness) according to the following evaluation criteria.

[0065] Appearance (graininess) A: The rice grains are individually shaped like individual grains, which is good. B: The shape of the rice grains appears to be similar to grains, but some of the outlines are difficult to see, so it is fairly good. C: The rice is not separate like grains and looks clumped together, making it defective.

[0066] Texture (stickiness and hardness) A: Good, with moderate viscosity and hardness. B: Somewhat sticky and hard in some areas, fairly good. C: Hard and not sticky, so it is defective.

[0067] ·comprehensive evaluation A: It is good because it has good grains, is soft, and has moderate stickiness. B: The grains are somewhat difficult to notice, but the product is soft and has a moderate stickiness, or the texture is strange, but the grains are well-defined, so the product is fairly good. C: The graininess is somewhat difficult to discern and the texture is strange, so it is somewhat unsatisfactory. D: No graininess or poor texture, poor quality.

[0068] [Table 1]

[0069] As described above, according to the manufacturing method of the present invention, the cooked rice obtained had an excellent texture with appropriate stickiness and hardness and a well-defined grain shape, even after undergoing freezing, thawing and the subsequent chilling process. In contrast, the frozen rice of Comparative Example 1, in which the pressure in the heating and pressurizing step was above the upper limit of the present invention, lost its grainy shape and had an excessively soft texture. Also, the rice of Comparative Example 2, in which both heating steps were performed at normal pressure, was not sufficiently gelatinized.

[0070] In Comparative Example 3 corresponding to Patent Document 2, the center part was not gelatinized in the heating and pressurizing step, so the resulting cooked rice was not sufficiently gelatinized. In Comparative Example 4, in which the steaming step was pressurized and heated, the rice contained a lot of moisture, and when pressed, the appearance and texture became poor. Similarly, the cooked rice of Comparative Example 5 corresponding to Patent Document 3 was not sufficiently gelatinized in the heating and pressurizing process, and the cooked rice of Comparative Example 6, in which the steaming process of Comparative Example 5 was replaced with pressurized heating, had a high moisture content and the appearance and texture became poor when pressurized.

[0071] 3. Frozen rice production 2 (non-glutinous rice) Example 7 Non-glutinous rice (low amylose rice, variety: Milky Queen) was used instead of glutinous rice in Example 1. Except for this, frozen cooked rice was obtained in the same manner as in Example 1.

[0072] Comparative Example 7 In Example 7, instead of the heating and pressurizing step, steaming was performed at normal pressure at 100°C for 15 minutes, and the second water absorption step was not performed. Except for this, frozen cooked rice was obtained in the same manner as in Example 1.

[0073] 4. Evaluation of frozen cooked rice during and after thawing 2 The frozen cooked rice produced in each Example and Comparative Example was stored in a freezer (-18°C) for 2 weeks, then transferred to a refrigerator at 7°C and stored at 10°C for 6 hours, and then left to stand at room temperature (25°C) for 10 minutes.

[0074] The samples after standing were evaluated in the same manner as in "2. Thawing of frozen cooked rice and evaluation after thawing 1" above. The results are shown in Table 2.

[0075] [Table 2]

[0076] As shown in Table 2, even when non-glutinous rice is used as the raw rice, the manufacturing method of the present invention effectively prevents quality deterioration due to thawing and chilled storage.

[0077] Evaluation 3: The physical properties of the cooked rice obtained in Examples 1 and 4, Comparative Example 2, and Examples 5 and 6 were measured by the following methods. The following procedure was carried out using a Tensipressor manufactured by Takemoto Denki Co., Ltd.: (1) Frozen cooked rice was placed in a refrigerator at 7°C and then thawed for 72 hours. One cooked rice grain was crushed with a puncture probe (Φ30 mm) at a speed of 1 mm / s until the distortion rate reached 90%. (2) The maximum stress (A) at this time was evaluated as the hardness of the entire rice grain. (3) After that, the sum of the continuing adhesive forces (B) when the strain rate was returned to 0% using a puncture probe (Φ30 mm) at a speed of 1 mm / s was evaluated as the stickiness value of the entire rice grain. The results are shown in Table 3.

[0078] [Table 3]

[0079] The results in Table 3 also show that the use of a specific heating and pressurizing process can reduce hardness and improve viscosity.

Claims

1. A soaking process in which the raw rice is soaked in water at 10 to 35 degrees Celsius to absorb the water; a heating and pressurizing step of steaming the rice after the soaking step with saturated steam under a pressure of 130 to 200 kPa; A water absorption process in which water not exceeding 60°C is added to the rice after the heating and pressurizing process and the rice is absorbed. A freezing step of freezing the rice after the water absorption step.

2. The method for producing cooked rice according to claim 1, wherein in the soaking step, the rice is soaked until the water content is 36 to 45% by mass.

3. The method for producing cooked rice according to claim 1 or 2, wherein in the water absorption step, the rice is allowed to absorb water so that the water content is 57 to 75% by mass.

4. a second heating step in which the raw material rice after the water absorption step is subjected to a heat treatment by steaming under normal pressure so that the moisture content is 43 to 60% by mass; The method for producing cooked rice according to claim 1 or 2, further comprising a second water absorption step of adding water having a temperature not exceeding 60°C to the raw material rice after the second heating step, and allowing the raw material rice to absorb water so that the water content is 57 to 75% by mass.

5. Cooked rice produced by the method according to claim 1 or 2.

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