Buzz
How much do you really know about microwaves?
Image courtesy of Panasonic and Matsushita Electric Corporation of AmericaThe microwave oven is often hailed as one of the most significant inventions of the 20th century — it has become a staple in hundreds of millions of homes across the globe.
Consider how often you rely on a microwave throughout your day. You’re running late, so there’s no time to prepare breakfast. You swing by a gas station, grab a frozen breakfast burrito, and microwave it. Later, during a busy afternoon at work, you grab a snack-sized bag of microwave popcorn from the vending machine and heat it up in the break room. After a long workday, you’re too tired to cook, so you reheat yesterday’s lasagna in the microwave.
Clearly, microwave ovens are so popular because they cook food in mere minutes. These household essentials are also remarkably energy-efficient, as they focus their heat on the food, not the container holding it. In this article, we’ll delve into the fascinating science behind microwave cooking and the secret to these “meals in a minute.”
Microwave Technology
Image provided by Panasonic and Matsushita Electric Corporation of AmericaIt’s no surprise that a microwave oven utilizes microwaves to heat food. Microwaves are a type of wave found between radio waves and infrared radiation on the electromagnetic spectrum. The frequency typically used in microwave ovens is around 2,450 megahertz (2.45 gigahertz).
Waves within this frequency range have a unique characteristic: They are absorbed by water, fats, and sugars. When absorbed, these materials convert the waves into atomic motion, which generates heat. Interestingly, these waves aren’t absorbed by most plastics, glass, or ceramics. Metal, however, reflects microwaves, which is why metal cookware isn’t suitable for use in a microwave oven. This reflective property is also why microwave ovens have metal walls.
Microwave Cooking Process
Image provided by Panasonic and Matsushita Electric Corporation of AmericaYou may have heard the phrase that microwave ovens cook food "from the inside out." But what does that actually mean? Let’s break it down to better understand how microwave cooking works.
Imagine you’re baking a cake in a traditional oven. Typically, you’d bake it at 350 degrees F (177 degrees C), but this time you mistakenly set the oven to 600 degrees F (316 degrees C). What do you think will happen? The cake's outer layer will burn before the inside has even begun to warm up.
In a conventional oven, heat must travel (via conduction) from the outside of the food toward the center (refer to How a Thermos Works for a detailed explanation of conduction and other heat transfer methods). The dry heat on the outside of the food evaporates moisture, allowing the exterior to crisp up and brown (for example, bread forms a crust) while the interior remains moist.
In microwave cooking, the radio waves penetrate the food and excite the water and fat molecules almost uniformly throughout. There’s no need for heat to travel inward by conduction. The heat is distributed evenly right away because the molecules all begin vibrating together. Of course, there are limitations. Microwaves don’t penetrate thick food evenly (they may not reach the center), and there are also “hot spots” from wave interference, but you get the general idea. The whole heating process is different because it involves "exciting atoms" rather than "conducting heat."
In a microwave oven, the air inside remains at room temperature, meaning it can't create a crispy crust. This is why microwavable pastries often come with a small foil and cardboard sleeve. When you place the food inside and microwave it, the sleeve absorbs the microwave energy and becomes very hot. This heat on the outside allows the crust to crisp up, mimicking the effect of a conventional oven.
