Cooking With Magnetism (For Real)

Vincent T.
0xMachina
Published in
6 min readFeb 17, 2020

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Let’s cook with electromagnetism.

Everyday, people cook their food using something they may not have expected. Magnetism. That’s correct MAGNETISM as in “magnets”. We use a common kitchen appliance that puts magnetism to work. The appliance I am referring to is the humble and very simple rice cooker. Restaurants and households all over the world have used this appliance to cook steamed rice of all sorts. Rice is a staple in many places that is eaten with a main dish. You can either cook the traditional way by fire and stove, or just use the easiest way of cooking rice … the rice cooker.

I find the rice cooker to be one of the world’s greatest inventions, after the telephone, television and computer. It helps provide our every day nutritional needs quickly with a push of a button. Rice itself is a great filler for meat and vegetable dishes, very much like bread. The advantage with rice is that it is easier to cook, taking at most 20 minutes while bread is a more lengthy chore. You have to mix the flour and water, knead the dough, etc. There is also no instant “bread cooker” unless you buy the pre-made dough and put it into the oven. Rice is still much easier to make, and you don’t have to worry too much about cooking the perfect rice. Rice consists of just one ingredient, while with bread it requires a mix of ingredients that can have different results if not in the right proportions.

Some people think that the rice cooker is just a pot where you put rice and water (obviously, but wait … there’s a lot more). You then turn on a button and several minutes later, you have fluffy rice that is steaming hot. Now here is where you might be wondering where does a magnet come into cooking rice?

Dissecting The Rice Cooker

The rice cooker consists of a main body that contains an electric heating plate and thermal sensor. It also contains a pot with a lid, which is inserted into the main body. An electrical cord from the main body is inserted into an AC outlet. Once the rice and water has been put in the pot, it is ready to be cooked. There is a mechanical button on the main body that is pressed down to turn on the appliance, while more sophisticated rice cookers use electronic control buttons.

The traditional rice cooker contains a main body with electrical cord and power switch and pot or pan with lid.

How It Works

When electrical current flows through resistive materials, it generates heat. The original rice cookers used the principle of resistive heating in order to heat a plate that then cooks the rice. Once heated, the water will reach boiling point (212° F, 100° C). Once all the water inside the pot has boiled into steam, the temperature will drastically increase. The thermal sensor or heat sensing device, will then switch off or go to a warming state in some rice cookers. The result is then steamed fluffy rice. That is the simplest operation of a rice cooker. Once again, where do magnets come into all this? It is not actually magnets, but the force of electromagnetism that is at play.

Today many rice cookers are electronic and rely on induction heating. The main body of the rice cooker, underneath the heating plate, contains copper coils. Once electric current is passed through those copper coils, they create a magnetic field, which is the process of induction. It generates the heat due to resistance from the magnetic field, from the process of hysteresis. This is due to the magnetic materials resistance to any fast-paced changes in their magnetic level. This can be from the magnetic material in the cooking pot (or pan).

A circuit diagram of induction heating. An MCU (Main Control Unit) provides signals to a Gate Driver. A discrete IGBT is used for fast switching and higher efficiency to the induction heater.

In the induction heating rice cooker (an induction heater that consists of an electromagnet and an electronic oscillator) a high-frequency AC current is passed through the electromagnet. Eddy currents are generated in the material of the heating plate that distributes the heat to the pot for cooking the rice. An electronic heat sensor or thermostat will detect when the water has evaporated by measuring the highest temperature inside the pot. It will then switch from a cooking to a heating state or turn off the rice cooker.

Actually, Magnets Are Used

Now you may also have heard that rice cookers do have magnets. That is also true, but that is in the assembly of resistive heating rice cookers. The magnet is actually also the thermostat or thermal sensing device in traditional rice cookers that use resistive heating. The magnet is attached to where the heating element meets the pot, and contains a spring. When the pot is put into the main body with the water and rice, the magnet is depressed pushing the spring downward to hold the switch that keeps a closed circuit with the heating plate.

A rice cooker magnet which also functions as a thermostat. (Source Amazon)

The magnet loses its magnetic property when they go above a certain temperature. The magnet in the switch loses its magnetism at temperatures above 100° C. This happens when all the water inside the pot has evaporated, now heating the inside of the pot and the rice, further increasing temperatures above 100° C. When this happens the magnet releases the switch and turns the rice cooker into a warming state or shuts off entirely. It is good to know this, but the magnet itself doesn’t cook the rice but aids in its cooking.

Advantages Of Induction Heating

The benefits of moving from resistive to inductive heating are huge. Inductive heating provides more efficiency and precision. Here are 3 reasons why.

  1. There is more accuracy due to the thermal sensing device, which can adjust the temperature electronically by varying the magnetic field.
  2. More precision in the heat level distribution when cooking inside the pot. The temperature can be adjusted electronically by either increasing or decreasing the magnetic field.
  3. Greater efficiency since the amount of heat is not at a constant peak level, like in traditional resistive heating rice cookers. The heat can vary with the conditions inside the pot, so it uses less energy.
An induction heating rice cooker (Source TIGER)

One Appliance, Many Uses

You can also use the rice cooker to cook other food items besides rice. It can be used to boil eggs, steam dumplings and even braising meats. The rice cooker can even be used to steam tamales. Newer generation rice cookers have evolved into multipurpose appliances with advanced electronic controls and sensors. Some rice cookers even use fuzzy logic with programmable electronic controllers. However, even the simplest rice cooker can steam, boil and braise food. Thanks to electromagnetism, induction heating brings newer features to the rice cooker which makes it all the more easier and efficient to cooking a popular staple food item and a lot more.

Let’s keep making those rice bowls.

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Vincent T.
0xMachina

Blockchain, AI, DevOps, Cybersecurity, Software Development, Engineering, Photography, Technology