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Introduction

Instant rice is a product that has been gaining popularity recently due to its quick preparation for consumers using only a microwave. The process of creating instant rice includes first cooking the rice, then dehydrating it and finally rehydration by the consumer at home. Producers who create instant rice aim to make the product as close to newly cooked rice as possible; they aim to make rehydration time short and have texture, colour and stickiness of cooked rice.

Researchers have conducted experiments to find the optimal conditions to use in order to meet the desired qualities for instant rice. They look for the best technique, temperature and time to use in order to let the rehydration process make the instant rice resemble cooked rice. In an experiment, it was found that the hardness and chewiness of instant rice that was rehydrated decreased as the moisture content of the rice and cooking pressure of the atmosphere increased. This finding is useful for producers who are always trying to improve their products. It is important however to note that optimal conditions can differ based on the technique used for cooking and dehydration as well as the type of rice used. For example, Brown rice may be processed with different conditions compared to White rice because brown rice has more layers (hull, bran and germ). Because white rice has those components removed, it will be easier to reach the desired soft texture upon cooking due to the water being able to penetrate the grain with more ease. Brown rice has a cooking time of approximately 45 minutes while white rice has a cooking time of approximately 20 minutes. Furthermore, lowering the cooking temperature of the rice may control the rate of water diffusion which is another factor that could affect the quality of the rice product.

This product has not been perfected yet like some other processed foods. After rehydration, the quality is different compared to cooked rice; it is less hard and less sticky due to the previous steps of preparation. Dehydrating techniques and methods that are used can affect the flavour and texture of the rice; further research is yet to be done in order to find the best possible way to process rice to make it resemble cooked rice which most people prefer due to its satisfying texture.

Preparation Process

Preparation

One method to prepare the rice is to soak it at 30°C to allow water absorption. Allowing some water absorption in the beginning will start softening the rice grain. Next, steam the rice with a steamer at 100°C for 5 minutes to start the gelatinization process. Soaking the rice at 90°C afterwards will retain over half of the moisture content (60-80%). Another 5 minutes of steam will then make the rice reach its desirable moisture content (62%).

Cooking

It is essential to take into account how the rice is cooked in order to attain the best results. There are many little factors during the cooking process that affects the quality of the rice. As stewing time increases, the moisture content of the food decreases. If the stewing time is over 40 minutes, this will result with an excessive loss in moisture. Decrease in moisture content will also increase the hardness of the rice, which can also be a result from cooking it at a high pressure for a long period of time due to an increase in gelatinization. In order to prepare the rice at the shortest amount of time, it is optimal to cook it at 45°C because that is when the water absorption is the fastest. In addition, some key factors that impact the production of the food are initial moisture before drying that affects the quality and appearance of the dried rice, degree of gelatinization, and drying techniques.

Methods

Boiling

1. Soak rice in water at a ratio of 1:1.3 respectively at room temperature for 10 minutes
2. Boil rice for 12 minutes
3. Wait 10 mins after cooking

Electric cooker

1. Add rice to water at a ratio of 1:1.5 respectively
2. Cook rice for 18 minutes
3. Wait 10 minutes afer cooking
4. After cooking, wash with water at ambient temperature or cool water for 30 seconds to prevent Agglomeration from happening

Rehydration Time

The rehydration time of the rice depends on the structure and porosity (number of pores in structure of the grain). Porosity can be created through drying and puffing. It can also change the water absorption capacity of the rice. However, porosity can be changed with different drying conditions and techniques. If the rice has a high drying rate then it is at its desired structure where rice is porous instead of dense, which is important for the rehydration process.

Dehydration

Drying is the most critical step for rehydration process. It is also referred to as puffing. Depending on the drying technique, it can change the colour, volume, rehydration capability, volume expansion, dry bulk density, and microstructure of the rice grain. When the rice is exposed to a high increase in water vapour pressure, it will go through structure changes and produce the porous structure. Depending on the puffing conditions, it can have an effect on hardness and stickiness for the rice, such as hardness is decreased with the increase in moisture content and high drying temperatures can lower stickiness. The more porous the rice grain is, the softer the texture after hydration. 

For brown rice, it can be prepared with the use of a microwave, which is beneficial with its fast drying rate due to the waves penetrating the insides making the moisture move to the surface rapidly. Freezing and thawing before microwave as a pretreatment can promote more of a sponginess taste because the ice crystals can expand the rice. For optimal conditions and the rice to taste as delicious as it can be, it is preferred to have the water to rice ratio of 1.44, microwave at the power level of 499.8W, and at a hot air temperature 89.99°C. 

Drying methods

Hot air drying or freeze drying. It is recommended that boiling and freezing prior to drying should be conducted as a method for producing instant rice

[Taikeng 9]: low-amylose japonica

• gelatinization temperature: 61.0-72.7°C

[Taichung Sen 10]: low-amylose indica

• gelatinization temperature: 61.4-74.8°C

[Taichung Sen 17]: high-amylose indica

• gelatinization temperature: 59.0-71.7°C

Fluidized bed drying is considered to be the most suitable technique for water removal. This technique allows for faster and more homogenous drying to the product. Furthermore, when comparing fluidized bed drying to tray drying, there is less change of physical and chemical changes to the product.

Food Science

Gelatinization

The process of the breakdown of starch granules in water with the presence of heat is known as gelatinization. During gelatinization, swelling of starch granules leads to cell explosion and the release of its content. Temperature affects the rate of water diffusion during cooking where the rate of gelatinization can be influenced. Starch granules become soft and pliable after this irreversible process. Some samples have been through two gelatinization processes whereas the outer surface of rice is softened in the first cycle and the rice is able to achieving better moisture content level in the second cycle.

Retrogradation

Retrogradation is regaining the crystallization of starch after gelatinization. Retrogradation takes place after gelatinization with less heat surrounded, and results in starch dehydration. Since instant rice is packaged and store at room temperature, retrogradation is necessary to produce instant rice.

Quality

The preparation of rice can overall affect the quality of the end product of instant rice. If the rice has extremely high quality during its cooking stages, then it may have a very high quality after the consumer rehydrates the rice at home.

Microwaving

Brown rice

Using a microwave as a technique for dehydration helps the quality of the rice remain intact due to its rapid heating. The microwave creates a porous structure instead of shrinkage to the rice grain that would be caused by tray Drying. With a microwave, the heat penetrates the centre of the rice grain quickly and allows for rapid release of water. Whereas in tray drying, the solutes would move up to the surface then the water would evaporate from heat causing a hard-shell. It is important to look at the microwave's power level as well as it can affect the texture of the rice due to the energy weakening interactions between the sugars that make up the rice.

Brown rice

The quality of the colour in brown rice decreases and becomes more dull as more time is given to drying the rice. This may be due to the concentration effect that takes place when the water leaves the rice. When the amount of water decreases, the reactants are more concentrated which may lead to more reactions taking place.

The quality of rehydrated instant brown rice is measured by looking at it's Starch gelatinization, colour, hardness and taste. However, we must keep in mind that taste can be often covered by flavours that are added to the product.

White rice

White rice

The microstructure of white rice can be slightly deformed if it is prepared from an electric rice cooker. However, using an electric rice cooker makes the rice softer and drier than by simply boiling the rice. If this happens, then the end product of the rehydrated instant rice product could have a lower quality since it will need to be processed further. When cooked white rice is frozen in preparation for the dehydration step, the rehydrated rice at the end has a desired texture that resembles cooked rice. This freezing pre-treatment can also affect the colour of the instant rice if it is dehydrated under 160°C. Rehydrated rice that is found to be less sticky than fresh cooked rice is likely to be due to drying techniques and conditions but not the freezing pre-treatment.

Packaging

Characteristics of container

Packaging of Minute Rice's instant rice.

The container used to store instant rice needs to be made out of a material that is microwave-safe as well as allow the waves to be transmitted into the rice itself to heat it up. Having the container itself being as the dishware will give consumer the benefit of not having to clean up afterwards as they are able to simply throw it away. Furthermore, there is no need to drain water after microwaving.The shapes of the containers can vary from a cup, inverted cone, cylinder, a tray, and much more. It is important that there is a Hermetic seal between the body of the container and the lid so that the contents may have less risk of escaping the container as well as ensuring the container is full is steam so that the rice can be heated.

These types of containers can also be used for instant noodles, macaroni, pasta and many other instant foods.

Advantages

• Quick
• Acceptable quality
• No draining required
• Minimizes work needed by consumer

Disadvantages

• Must be designed to specifically fit food and be cooked properly
• Produces lots of waste