JP7531391B2 - Cooked rice manufacturing method - Google Patents

Description

The present invention relates to a method for cooking rice, and more specifically, to a method for cooking raw rice that has not been soaked in water.

In recent years, the demand for rice balls and boxed lunches displayed at convenience stores and supermarkets has increased, as has the demand for cooked rice (cooked rice), which is cooked in large quantities by manufacturers and kept at room temperature, refrigerated, or frozen for relatively long periods of time. When cooking rice, it is common to have a water soaking process in which the rice is soaked in water as a process before cooking begins. From the perspective of increasing the production efficiency of cooked rice, a short soaking time is preferable, but if the soaking time is too short, the cooked rice will have a hard core due to the low moisture content. Patent Document 1 describes a method for producing cooked rice with a significantly shorter soaking time, which includes a process in which raw rice that has not been soaked in water is placed in an atmosphere of superheated steam while being sprayed with water.

Patent Document 2 describes a method for producing okowa rice balls, which involves the steps of soaking in water, draining, cooking, and vacuum cooling, in which after the cooking step and before vacuum cooling, the surface of the steamed rice grains obtained in the cooking step is coated with a seasoning liquid containing polysaccharides derived from seaweed. According to the manufacturing method described in Patent Document 2, the action of the seasoning liquid prevents excess water from evaporating from the steamed rice during vacuum cooling, so the produced okowa rice balls are not dry.

JP 2014-226062 A JP 2010-284139 A

The objective of the present invention is to provide a technology that can efficiently produce high-quality cooked rice with appropriate hardness and stickiness without the need for soaking in water before cooking.

The present invention is a method for producing cooked rice that uses raw rice as the raw material rice, and includes a steam heating process in which the raw material rice is heated by applying steam at 80 to 100°C, and a liquid treatment process in which the raw material rice is brought into contact with a treatment liquid, the treatment liquid having a viscosity of more than 0.9 mPa·s and not more than 80 mPa·s at a product temperature of 25°C.

The present invention provides a method for producing cooked rice that does not require soaking in water before cooking and can efficiently produce high-quality cooked rice with appropriate hardness and stickiness.

The method for producing cooked rice of the present invention includes a steam heating step in which raw rice is heated by applying steam to the raw rice, and a liquid treatment step in which the raw rice is brought into contact with a treatment liquid. The steam heating step is a step in which the raw rice is cooked, and the liquid treatment step is a step carried out for the purpose of improving the texture of the cooked rice.

In the present invention, raw rice is used as the raw material rice. In the present invention, "raw rice" refers to untreated raw rice that has not been soaked in water. In addition, "not soaked in water" here refers to raw rice that has not substantially absorbed water, and does not include, for example, raw rice that has been washed with water immediately before being used to produce cooked rice.
The type of raw rice is not particularly limited and may be appropriately selected depending on the type of cooked rice to be produced. Raw rice that can be used in the present invention includes, for example, non-glutinous rice, glutinous rice, or a combination thereof. Non-glutinous rice includes low amylose rice, high amylose rice, and normal non-glutinous rice. These may be used alone or in combination of two or more types. Typically, non-glutinous rice is used.
The polishing ratio of raw rice is not particularly limited and may be appropriately selected depending on the type of cooked rice to be produced. Raw rice that can be used in the present invention includes, for example, white rice, pre-washed rice, brown rice, 70% polished rice, germ rice, raw rice from which bran, etc. have been removed by wind, etc. These may be used alone or in combination of two or more types.

In the steam heating process, raw rice (raw rice) is heated by applying steam at 80 to 100°C. If the steam temperature is below 80°C, the rice will not be cooked sufficiently and the rice may become too hard, whereas if the steam temperature exceeds 100°C (i.e., superheated steam is applied to the raw rice), the heating temperature is too high and this may result in the surface of the rice drying out or the rice being overheated. The temperature of the steam is preferably 85 to 100°C, more preferably 90 to 100°C.

The time for which steam is applied to the raw rice in the steam heating step (steam treatment time) is not particularly limited and may be appropriately selected depending on the type of raw rice, etc. If the steam treatment time is short, the cooked rice will have a low moisture content and will be hard with a core, and the cooked rice will tend to have a dry and undesirable texture. If the steam treatment time is too long, the cooked rice will tend to have a high moisture content and will tend to have a sticky and undesirable texture. From the viewpoint of further improving the texture of the cooked rice, the steam treatment time is preferably 10 to 60 minutes, more preferably 15 to 50 minutes, and even more preferably 20 to 45 minutes. Note that the "steam treatment time" referred to here means the total time for which steam is applied to the raw rice to be treated. For example, if the treatment of applying steam to the raw rice is carried out in multiple steps, it means the total time for the multiple treatments.

The method of applying steam to the raw rice in the steam heating step is not particularly limited. The steam applied to the raw rice may or may not be saturated steam. For example, the method may be one in which steam is applied to raw rice placed in a non-sealed space and open to the atmosphere, or one in which steam is applied to raw rice placed in a sealed space. One example of a method of applying steam to raw rice is a so-called batch method in which raw rice is placed in a sealed or non-sealed space and steam is supplied to the space. Another example of a method of applying steam to raw rice is a so-called continuous method in which raw rice is continuously transported along a conveying path such as a belt conveyor placed in a non-sealed space while steam is supplied to the space.

During the steam heating step, the raw material rice to be treated may be stirred using a stirring tool such as a rice scoop. Such a stirring operation can prevent unevenness in the cooked rice.
In addition, in the steam heating step, a treatment of heating the raw material rice may be carried out in parallel with the treatment of applying steam to the raw material rice.

By steam treating raw rice such as the steam heating process, it is possible to cook rice without a water soaking process of soaking the rice in water, which shortens the production time of cooked rice and improves production efficiency. However, it has been found that cooked rice obtained by conventional steam treatment has problems in terms of texture, such as being dry and having low stickiness.
The liquid treatment step is adopted to solve the problem of steam treatment of raw rice, and is characterized in that the raw rice is contacted with a treatment liquid having a viscosity of more than 0.9 mPa·s and not more than 80 mPa·s at a product temperature of 25°C. By adopting the liquid treatment step in addition to the steam heating step, it is possible to efficiently produce high-quality cooked rice having appropriate hardness and stickiness. If the viscosity of the treatment liquid is less than 0.9 mPa·s or more than 80 mPa·s, it is not preferable because it has little effect on improving the texture of the cooked rice. The "viscosity" referred to here is a value measured using a B-type viscometer in accordance with JIS Z 8803 "Viscosity of liquids - Measurement method". The viscosity of the treatment liquid is preferably 70 mPa·s or less, more preferably 60 mPa·s or less. The lower limit of the viscosity of the treatment liquid, 0.9 mPa·s, is a viscosity slightly higher than the viscosity of water at a water temperature of 25°C. That is, assuming that the viscosity of the treatment liquid is greater than the viscosity of water at a temperature of 25° C., it is preferably 1 mPa·s or more, and more preferably 1.5 mPa·s or more.

The treatment liquid is not particularly limited in composition as long as it has a viscosity within the specific range at a product temperature of 25°C. Typically, the treatment liquid contains water as a main component and further contains a thickener to impart a higher viscosity than water, specifically, to make the viscosity at a product temperature of 25°C greater than 0.9 mPa s.
As the thickener, any edible polymeric substance that dissolves or disperses in water to produce viscosity can be used without particular limitation. Examples of the thickener include gelling agents and thickening polysaccharides. One of these can be used alone, or two or more can be used in combination.
Examples of the gelling agent include gelatin, agar, carrageenan, and pectin.
Examples of the thickening polysaccharides include processed starch, disaccharides such as sucrose, and polysaccharides having three or more sugars. The processed starch is a general term for starch that has been subjected to physical, enzymatic, or chemical processing. Examples of starch that can be used as the raw material for the processed starch include tapioca starch, wheat starch, corn starch, potato starch, and rice starch. The processing method of starch to obtain the processed starch is not particularly limited, and examples of the processing include crosslinking, esterification, etherification, and oxidation, and two or more types of processing methods may be combined.

Among the thickeners, thickening polysaccharides are preferred, particularly polysaccharides of three or more sugars, because they have an excellent effect of improving the texture of cooked rice. That is, the treatment liquid used in the liquid treatment step preferably contains thickening polysaccharides, particularly polysaccharides of three or more sugars. Examples of polysaccharides of three or more sugars include guar gum, white fungus polysaccharide, xanthan gum, locust bean gum, and tamarind gum.
The white wood ear polysaccharide is a white wood ear extract containing polysaccharides derived from white wood ear, or a composition mainly composed of the white wood ear extract. The white wood ear polysaccharide may be a polysaccharide polymer containing α-1,3-mannose in the main chain and D-fucose, D-xylose and D-glucuronic acid in the side chain. As the white wood ear polysaccharide, for example, one described in JP 2019-41735 A can be used. As the white wood ear polysaccharide, a commercially available product can be used, and one example thereof is "Tremel Gum" manufactured by Unitec Foods Co., Ltd.

The content of the thickening agent in the treatment liquid may be adjusted so that the viscosity of the treatment liquid at a product temperature of 25°C falls within the above-mentioned specific range, but from the viewpoint of ensuring the action and effect of the thickening agent (the effect of improving the texture of cooked rice), the content of the thickening polysaccharide in the treatment liquid is preferably 0.01 to 0.2% by mass, more preferably 0.02 to 0.15% by mass, based on the total mass of the treatment liquid.

When the processing liquid contains a thickener, in order to ensure that the thickener exerts its action and effect more reliably, it is preferable to add the thickener in the liquid processing step in an amount of preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.11 to 0.7% by mass, and particularly preferably 0.15 to 0.6% by mass, as solid content, relative to the total mass of the raw rice (raw rice). If the amount of thickener added is too small, there is little point in using the thickener, and if the amount of thickener added is too large, the taste and texture of the cooked rice may be reduced, and the viscosity of the processing liquid may increase, making it difficult to spray the processing liquid, making it difficult to contact the processing liquid with the raw rice. In the liquid processing step, it is preferable to adjust the content of the thickener in the processing liquid, the contact method and contact time of the processing liquid with the raw rice, and, if the processing liquid is sprayed on the raw rice, the spray time and spray amount, etc., so that the amount of thickener added as solid content to the raw rice is within such a preferred range.

The processing liquid may contain additives other than the thickener, provided that the effect of the present invention is not impaired. Examples of additives other than thickeners include seasonings such as salt, sugar, sweeteners, 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; colorants, flavorings, preservatives, shelf life enhancers, and the like, and these may be used alone or in combination of two or more.

The method of contacting the raw rice with the treatment liquid in the liquid treatment step is not particularly limited, and examples include a method of spraying the raw rice with the treatment liquid, a method of immersing the raw rice in the treatment liquid, and a combination of multiple methods. From the viewpoint of improving production efficiency, a method of spraying the raw rice with the treatment liquid is preferred. Although the method of spraying the treatment liquid is not particularly limited, spraying using a spraying means such as a spray is preferred from the viewpoint of uniformly applying the treatment liquid to the entire raw rice.

In the liquid treatment step, the temperature of the treatment liquid when it is sprayed or otherwise brought into contact with the raw rice is not particularly limited, but in particular when the liquid treatment step is carried out during the steam heating step, the heating temperature or a temperature relatively close to this is preferred from the viewpoint of not inhibiting the heating of the raw rice by steam, specifically, preferably 30 to 90°C, more preferably 50 to 80°C.

The spray time when spraying the processing liquid on the raw rice may be adjusted appropriately according to the viscosity of the processing liquid, the content of a thickener if the processing liquid contains a thickener, etc., and is not particularly limited, but is preferably minutes. The spray time of the processing liquid is 1 to 60 minutes, more preferably 2 to 50 minutes, and even more preferably 3 to 40 minutes. The preferred range of the spray time of the processing liquid is particularly effective when the processing liquid contains a thickener in the preferred range described above. If the spray time is too short, there is little point in providing the liquid processing step, and if the spray time is too long, the contact time between the raw rice and the processing liquid will be too long, and the cooked rice may have a sticky and undesirable texture. Note that the "spray time" here means the total time for spraying the processing liquid on the raw rice, and for example, if the liquid processing step is performed in multiple steps, it means the total time of the multiple liquid processing steps.

When spraying the processing liquid onto the raw rice, the amount of spray may be adjusted appropriately depending on the viscosity of the processing liquid, and if the processing liquid contains a thickener, the amount of the thickener, etc., and is not particularly limited, but is preferably 50 to 500 parts by mass, and more preferably 100 to 300 parts by mass, per 100 parts by mass of raw rice. This preferred range of the amount of sprayed processing liquid is particularly effective when the processing liquid contains a thickener in the preferred range described above. Note that the "amount sprayed" here means the total amount of processing liquid sprayed onto the raw rice, and for example, when the liquid processing step is carried out in multiple steps, it means the total amount of sprayed processing liquid in each liquid processing step.

During the liquid treatment process, specifically, for example, while the treatment liquid is being sprayed onto the raw rice or after the treatment liquid has been sprayed onto the raw rice, the raw rice may be stirred using a stirring tool such as a rice scoop. This stirring operation distributes the treatment liquid (thickening agent in the treatment liquid) added to the raw rice evenly throughout the raw rice, so that the effect of the treatment liquid (improvement of the texture of cooked rice) can be more reliably achieved.

In the present invention, the order of carrying out the steam heating step and the liquid treatment step is not particularly limited, and both steps may be carried out simultaneously or sequentially. In the latter case, the steam heating step may be carried out first, followed by the liquid treatment step, or vice versa.
In a preferred embodiment of the method for producing cooked rice of the present invention, both steps are carried out simultaneously, i.e., the liquid treatment step is carried out during the steam heating step. More specifically, the raw material rice is heated by applying steam at 80 to 100°C, while the treatment liquid is sprayed onto the raw material rice at an appropriate timing.

In the present invention, the liquid treatment step may be carried out continuously or in multiple batches. An example of the latter is a case where the liquid treatment step is carried out during the steam heating step, and the liquid treatment step is carried out in multiple batches.

The present invention can be practiced, for example, using a cooked rice production device that includes a steam chamber into which steam is supplied, a belt conveyor disposed inside the steam chamber for transporting raw rice, and a nozzle for spraying a treatment liquid from above the raw rice transported by the belt conveyor. In this case, steam at 80 to 100°C is supplied into the steam chamber, and while the raw rice being transported inside the steam chamber by the belt conveyor is heated by the steam (steam heating process), treatment liquid is sprayed from the nozzle toward the raw rice (liquid treatment process). By devising the arrangement of the nozzle, the liquid treatment process can be carried out continuously or in multiple steps.

The method for producing cooked rice of the present invention may further include, in addition to the steam heating step and the liquid treatment step, a cooling step and/or a molding step of the cooked rice obtained through both steps.
In the cooling step, the method for cooling the cooked rice is not particularly limited, and examples thereof include cooling the cooked rice by loosening the cooked rice with a rice scoop, cooling under differential pressure, vacuum cooling, or a combination thereof.
The forming step is a step of forming cooked rice into a predetermined shape, and can be carried out according to a conventional method using a mold, a container, etc. In the forming step, a known forming means such as a serving device for serving cooked rice in a lunch box, a rice ball forming machine, a sushi robot, etc. can also be used.

The method for producing cooked rice of the present invention may further include a water treatment step of contacting the raw material rice with water, in addition to the liquid treatment step. By adopting the water treatment step, in combination with the steam heating step, it becomes possible to cook rice more reliably.
The water treatment step is preferably carried out during the steam heating step. The water treatment step may be carried out continuously or in a plurality of separate steps. There are no particular limitations on the method for bringing the raw material rice into contact with water in the water treatment step, but from the viewpoint of improving production efficiency, a method in which a treatment liquid is sprayed onto the raw material rice is preferred. When spraying water onto the raw material rice, the amount of water sprayed is not particularly limited, and may be appropriately adjusted so as to achieve the desired hardness of cooked rice.
For example, during the steam heating step, the liquid treatment step can be performed by spraying a treatment liquid, and the water treatment step can be performed by spraying water. In this case, spraying of the treatment liquid and spraying of water may be performed simultaneously or at different times.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[Examples 1 to 8, Comparative Examples 1 to 3, Reference Example 1]
Koshihikari (raw rice, no-rinse rice) produced in Niigata Prefecture was used as the raw rice to produce cooked rice. Specifically, 300 g of raw rice was placed in a steam-permeable container with an opening at the top, and the raw rice together with the container was placed in a steam chamber, and saturated steam at a predetermined temperature (see the "Temperature of steam" column in Tables 1 and 2) was continuously supplied to the steam chamber for a predetermined time (see the "Steam treatment time" column in Tables 1 and 2) to apply the steam to the raw rice in a state exposed to the atmosphere and heat it. During this steam heating process, a liquid treatment process was carried out twice in which the raw rice was brought into contact with a treatment liquid ("thickener-containing water" which is a mixture of water and a thickener) shown in Tables 1 and 2. The time interval between the liquid treatment process and the next liquid treatment process was 1 to 12 minutes. In each liquid treatment step, the treatment liquid was sprayed from the upper opening of the container toward the raw rice in the container, and the amount of treatment liquid sprayed in each liquid treatment step was 35 to 45 mL/min per 100 parts by mass of raw rice. The "amount of treatment liquid sprayed (parts by mass) per 100 parts by mass of raw rice" in Tables 1 and 2 is the total amount sprayed in all liquid treatment steps, and the "spraying time of treatment liquid" in Tables 1 and 2 is the total spraying time in all liquid treatment steps. The viscosity of the treatment liquid listed in Tables 1 and 2 was measured using a B-type viscometer (TVB-20L, manufactured by Toki Sangyo Co., Ltd.) at 60 rpm, one minute after the rotor started rotating, in accordance with JIS Z 8803 "Viscosity of liquids - Measurement method."

[Evaluation test]
For each of the Examples, Comparative Examples, and Reference Examples, the sprayability of the treatment liquid during the production of cooked rice was evaluated according to the following evaluation criteria. In addition, the cooked rice produced in each of the Examples, Comparative Examples, and Reference Examples was cooled for 20 minutes with cold air at 15°C immediately after production, and then eaten by a panel of experts, who evaluated the texture (stickiness, hardness) according to the following evaluation criteria. The results are shown in Tables 1 and 2.

<Evaluation Criteria for Sprayability of Treatment Liquid>
A: Good because the treatment liquid can be sprayed evenly onto the rice.
B: Fairly good because the treatment liquid can be sprayed onto the rice.
C: Poor because the viscosity of the treatment liquid was too high to spray.
<Evaluation criteria for stickiness of cooked rice>
A: Moderately sticky, good.
B: Not dry but not too sticky, so somewhat good.
C: Feels dry, so is poor.
<Evaluation criteria for cooked rice hardness>
A: Moderately soft, good.
B: Fairly good, as some hardness remains.
C: Too hard or too soft, poor.

As shown in Table 1, in each Example, the viscosity of the treatment liquid used in the liquid treatment process at a product temperature of 25°C was greater than 0.9 mPa·s and less than 80 mPa·s, and therefore the sprayability of the treatment liquid and the texture of the cooked rice (stickiness, hardness) were superior to the comparative examples that did not meet this requirement. Comparative Example 1 used water as the treatment liquid, resulting in inferior quality of the cooked rice compared to the examples, and Comparative Examples 2 and 3 had a viscosity of the treatment liquid at a product temperature of 25°C that exceeded 80 mPa·s, and therefore the treatment liquid could not be sprayed, and the cooked rice could not be evaluated.

The thickeners in the treatment solutions are different between the Examples in Table 2. Among the Examples in Table 2, Examples 4 and 5 were particularly highly evaluated, which shows that polysaccharides of trisaccharides or more are particularly effective as thickeners.

Claims (7)

A steam heating process is performed by using raw non-glutinous rice as the raw material rice and heating the raw material rice with steam at 80 to 100 degrees Celsius.
A liquid treatment step of contacting the raw material rice with a treatment liquid,
The method does not include a step of soaking the raw material rice in water prior to the steam heating step and the liquid treatment step,
The method for producing cooked rice, wherein the treatment liquid comprises a thickener and water, and has a viscosity of more than 0.9 mPa·s and not more than 80 mPa·s at a product temperature of 25°C. The method for producing cooked rice according to claim 1, wherein the raw rice is exposed to steam for 10 to 60 minutes in the steam heating step. The method for producing cooked rice according to claim 1 or 2, wherein in the liquid treatment step, the raw rice is sprayed with the treatment liquid, and the spraying time of the treatment liquid is 1 to 60 minutes. The method for producing cooked rice according to any one of claims 1 to 3, wherein the thickener is a polysaccharide having three or more sugars . The method for producing cooked rice according to claim 4, wherein the thickener is added in an amount of 0.05% by mass or more in terms of solid content relative to the total mass of the raw material rice in the liquid treatment process. The method for producing cooked rice according to any one of claims 1 to 5, wherein the liquid treatment step is carried out during the steam heating step. The method for producing cooked rice according to any one of claims 1 to 6, in which the liquid treatment step is carried out in multiple steps.