How Rice Cookers Work


An early poster advertises Toshiba's automatic rice cookers to overseas markets.
An early poster advertises Toshiba's automatic rice cookers to overseas markets.
Image courtesy of TOSHIBA

Burned chunks or gooey paste can be the disappoin­ting result of rice gone wrong, but with the use of a rice cooker, the odds even up for even the klutziest in the kitchen.

Rice is a staple in many people's diets around the world. The grain is especially important, both nutritionally and culturally, in Southeast Asia, so it's no surprise that Japan introduced the first household electric rice cooker. That first model was made by Toshiba in 1955, and other companies soon joined the market, adding innovations that expanded the abilities and features available in rice cookers. Replacing the conventional cast-iron pots of the day, which cooked over a coal stove, rice cookers freed Japanese homemakers from the tiresome task of carefully monitoring endless pots of rice [source: Web-Japan.org].

­­Rice cookers are geared primarily for rice but can be very versatile in their uses. Some people even use rice cookers as their primary cooking tool, for everything from spaghetti to spare ribs to scrambled eggs.

For a closer look at how rice cookers operate -- from the more basic models to the high-tech ones laden with all the bells and whistles -- let's begin with how they know to progress from one step of the cooking process to the next.

Rice Cooker Basics

The inner workings of a typical rice cooker
The inner workings of a typical rice cooker
HowStuffWorks 2008

Rice needs two things to evolve from a hard, little grain to big, fluffy morsels -- lots of water and lots of heat. For this reason, cooking rice happens in four phases:

  1. Sitting in water
  2. Boiling
  3. Absorbing water (steaming)
  4. Resting

Rice cookers automatically guide rice through these four stages. The appliance consists primarily of a main body, an inner cooking pan, an electric heating plate, a thermal-sensing device and some buttons.

Water and rice sit inside the cooking pan while it's inserted into the rice cooker's shell. The pan's weight depresses the thermal-sensing device, and the heating plate quickly brings the water to a boil. The sensing device is a small, spring-loaded thermometer that gauges the temperature of the pan's contents. It's set into the bottom of the rice cooker's main body.

Simple rice cookers usually warm their contents by transferring heat from the heating plate to the cooking pan, and the type of metal used can improve that transfer. Some metals -- copper and aluminum for example -- are highly conductive. In other words, they transfer their heat easily. A wide range of materials can be used for the cooking pan, and each type may affect the overall time it takes to cook the food.

The process for cooking the rice is simple. Water boils at 212 degrees Fahrenheit (100 degrees Celsius), and once it reaches a steady boil, it won't get hotter. As long as there is water in the pan, the temperature should be stable. Once the rice absorbs all the water in the pan, the temperature will start to rise. The rice cooker senses this change and will either switch off or switch to a warming cycle. At this point, the rice has finished cooking and entered the resting stage.

While most rice cookers do not speed up the cooking process noticeably, they can accomplish the task with less mistakes and less fuss than the average person armed with a stovetop pot, especially when the cookers are equipped with fuzzy logic. Fuzzy logic lets a rice cooker react to what's happening in the pan, and we'll explore how it does this on the next page.

Fuzzy Logic and Rice Cookers

Photo Courtesy Consumer Guide Products

Fuzzy-logic rice cookers have computer chips that direct their ability to make proper adjustments to cooking time and temperature. Unlike basic rice cookers, which complete tasks in a single-minded, mechanical manner, the process behind the fuzzy-logic rice cookers needs a bit more explanation. The fuzzy sets theory, first proposed by UC Berkeley professor Lotfi Zadeh in 1965, laid the groundwork for fuzzy logic, which he also put forward in 1973. Fuzzy sets theory has to do with mathematical sets, or groups of items known as elements. In most mathematical sets, an element either belongs to the set or it doesn't. For example, a sparrow would belong to a set of birds, but a bat wouldn't. In fuzzy logic, though, elements can belong to sets in varying degrees. So since a bat has wings, it might belong to a set of birds -- but only to a certain extent. Fuzzy logic is basically a way to program machines so they look at the world in a more human way, with degrees of truth. Instead of cold, hard parameters and strict data sets, fuzzy logic assumes a more practical approach. Using numbers, it incorporates non-definitive words like "slightly" or "almost" into its decision-making processes. As a result, the use of fuzzy logic in rice cookers helps to ensure properly cooked rice because it gives the appliances the ability to make judgment calls similar to those a person might make, albeit typically better than those a hungry, impatient person might make.

Photo Courtesy Consumer Guide Products

Zojirushi's NHS-06 3-Cup Rice Cooker on the left uses basic rice-cooker technology; Zojirushi's NS-ZCC18 Neuro Fuzzy 10-cup version cooks with the help of fuzzy logic.

An example of when fuzzy logic might be called into action is when the rice is cooking too fast on a hot day. In a typical scenario, the fuzzy logic algorithm will take the form of an if/then statement such as, "If the rice is too hot, and it is continuing to heat up fairly quickly, then the heating element needs to be turned down."

While fuzzy-logic rice cookers function under the same premise as basic models, their mathematical programming can deliver a slew of customized cooking options. The trick to these capabilities is the rice cookers' ability to react, making precise fluctuations in cooking time and temperature depending on the program selected. These may include different keep-warm and quick-cook cycles for the optimum cooking of rice varieties like sushi rice, porridge rice, mixed rice, white rice, sweet rice and brown rice. Some models also offer texture settings, allowing people to select hard or soft and sticky or wet rice.­ ­

But even with all these features, fuzzy-logic rice cookers are not the most advanced rice cookers available. That prize goes to the models that also use induction heating

Induction Heating and Rice Cookers

Some rice cookers take precision a step further with the help of a technology called induction heating. While other rice cookers apply heat directly from an electrical plate underneath the inner cooking pan, induction-heating rice cookers get their heat from an alternating electric current from the wall outlet.

Induction heating, used for many applications beyond rice cookers, is achieved when this current passes through metal coils, typically made of copper. The movement of the current through these coils creates a magnetic field. It is into this magnetic field that the rice cooker's pan is inserted. The magnetic field produces an electrical current inside the cooking pan, and this generates heat. Heat can also be produced from this process if the rice cooker's pan is made out of a magnetic material. This is due to a phenomenon called hysteresis, in which magnetic materials show a resistance to any fast-paced changes of their magnetic level. This resistance creates friction, which contributes to the cooking heat.

Induction heating improves rice cookers in three main ways:

  1. The temperature-sensing methods can be more accurate, allowing for fine-tuned adjustments in temperature.
  2. The heat distribution area can encompass the inner cooking pan, not just radiate upwards from below, to produce more evenly cooked food.
  3. The level of heat being created in the cooking pan can be changed in an instant by strengthening or weakening the magnetic field that is generating it.

These elements create the biggest bonus of the induction heating rice cooker. In the event of a human measuring error, an induction heating rice cooker can make minute adjustments to both the time and the temperature of the selected program because of its sensitivity to temperature, and its precise ability to control it.

­­­

Using Rice Cookers Successfully

Different varieties of rice, like basmati and jasmine, offer enticing aromas and rich taste.
Different varieties of rice, like basmati and jasmine, offer enticing aromas and rich taste.

There are several things to keep in mind to make sure everything goes as planned when you're using a rice cooker. But before we go into that, let's look at the different varieties of rice you might be cooking, specifically the differences between brown and white rice.

While several common types of rice are simply different varieties of plant species in the Oryza genus, white rice typically differs from brown rice only in how much it has been polished. When rice is harvested, its natural husk, called its chaff, is usually polished off to create brown rice products. From there, more polishing in varying amounts can remove the bran layer, changing it from brown to white rice in stages. In addition to the bran layer, rice has a small portion called the germ attached to it, and this can be polished off as well. Once rice has been through this entire process, it is considered typical white rice.

When using most rice cookers, you should wash the rice prior to cooking. Unless you're cooking the aptly-named rinse-free variety, washing the rice is an important step to clean off any remaining particles from the production process, which in some countries can include talc. Rinsing the rice is also a good way to clean off any excess starch, which will make the rice less sticky. The one exception to this rule is large, fully-automated rice cookers that rinse the rice for you.

Another important tip is to keep the measuring cup that typically comes with a rice cooker. Measuring-cup volumes vary from country to country, and to make sure you're filling your rice cooker with the right amount of rice and water, you'll need that little cup. This is also important because most rice cookers have an optimum load capacity. For example, a rice cooker with a capacity of seven cups may work best when preparing four to six cups of rice. But try to cram in eight cups or go light and make one, and you probably won't enjoy the finished product.

It's also good to note that different varieties of rice require different amounts of water to cook properly. Many rice cookers feature measuring lines etched in the inner cooking pan, which are usually appropriate for short grain white rice and some types of brown rice. For other types of rice, follow instructions about how much water to add. The freshness of rice may also affect the amount of water and cooking times -- typically more water is needed for older rice.

­Now that you know the path to rice-cooker success, you need to choose the best one for your needs. The next section will help you select your perfect rice cooker.­­

How to Choose the Right Rice Cooker for You

A group of official rice taste testers dip their chopsticks into five varieties of rice, prepared in the electronic rice cookers sitting in front of them.
A group of official rice taste testers dip their chopsticks into five varieties of rice, prepared in the electronic rice cookers sitting in front of them.
Sam Yeh/AFP/Getty Images

A rice cooker can be a great product for people with a variety of needs. Rice cookers benefit students who need compact appliances for their dorm rooms, parents who need to program a ready-and-prepared dinner, or rice-challenged cooks who need extra help in the kitchen. So which rice cooker do you need?

Do I want a lot of features or just a cheap, get-it-done model?

More high-end models come with a bevy of advanced features and programs, which may figure into your decision on which one to buy. Bonus features include programs to keep rice warm and ready to eat, to speed up the cooking time, to reheat rice or to decide when the rice cooker will begin cooking.

Keep in mind that all those extra abilities will come with a few extra dollars tacked onto the price.

What size do I need?

When choosing a rice cooker, consider how much rice you want to prepare. If you plan to prepare rice just for yourself, buying a large-capacity rice cooker might create a poor-tasting final product. Rice cookers work best when used for their intended serving sizes so make sure you consider how much rice you'll cook on average. Along those lines, do you also want to prepare other foods in your rice cooker? If that's the case, purchase a rice cooker with a steaming tray. Insert the steaming tray, loaded with vegetables, above the water level. As the water boils off and evaporates while cooking the rice, released steam will also cook the vegetables.

What material d­o I want my food to be cooked in?

Something else to consider when looking for the right rice cooker is what kind of inner cooking pan you would prefer. Many people prefer models made of aluminum or stainless steel, with a nonstick coating for easy cleanup. Others may prefer more natural pans made from charcoal or clay, which are naturally nonstick without the artificial coating.

What other features should I look for?

Features like a see-through lid can help you monitor your meal's progress, and a steam vent in the lid helps prevent any bubbling over. Measuring lines on the inside of the cooking pan can also be a selling point for people who don't want to use a measuring cup.

To learn more about rice cookers and other handy kitchen gadgetry, explore the links on the next page.

Related HowStuffWorks Articles

­­More Great Links

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