You’d be hard-pressed to find a home without a microwave oven these days. These appliances make it easy to reheat and even cook some foods, as long as the required temperature can be reached in the microwave.
There’s no real highest temperature a microwave can reach, as microwaves don’t have heating elements like regular ovens. The heat is produced by the microwaved object and not the appliance. But since most foods have some amount of water, the maximum temperature they’ll reach is around 212°F (100°C).
The rest of this article explains how a microwave oven works and why it has no actual highest temperature. It also looks at the maximum temperature of microwaved objects and factors that can affect this temperature.
How a Microwave Oven Works
Contrary to what many people think, a microwave oven doesn’t actually heat food, at least not in the way that a stove or conventional oven does. Instead, what a microwave does is excite the molecules in your food, making them vibrate and rub against each other. As the molecules vibrate, they produce heat, much like how you generate heat when you rub your palms together.
When you turn on your microwave, it releases 12 cm (4.7 inches) radio waves into the cooking cavity. Just like your WI-Fi and television signals can pass through walls and doors, these 12 cm waves will pass through glass, ceramics, paper, and plastic. On the other hand, the waves will bounce off metal surfaces but will get absorbed by food.
As the microwaves pass through food, the molecules (particularly water, fat, and sugar molecules) flip back and forth, following the waves’ zig-zag pattern. The microwaves have a frequency of 2.45GHz, so they flip the molecules a whopping 2.45 billion times per second when they pass through food. This rapid back and forth movement is what causes the heat in the food and is also known as dielectric heating.
As stated, the waves pass through paper, plastic, glass, and ceramics. Any heat you notice on the container is from the hot food touching it, not the microwave.
Now to heat your food so quickly, the microwave employs several components. But the most important one is the Magnetron, which converts electricity to microwaves.
Other components include;
- A waveguide that channels the waves from the Magnetron to the food compartment
- A stirrer to circulate microwaves around the food compartment
- A turntable to rotate the food so that all sections are heated evenly
Here’s a three-minute animated video showing all that’s been said about the workings of a microwave oven.
The Highest Temperature a Microwave Can Reach
After seeing how a microwave works, you’ll agree that it’s not the appliance that gets hot but the food (or object) that’s inside. Even models with temperature probes are actually telling you how hot the food is and not how hot the microwave is.
So the right question isn’t “what’s the maximum temperature a microwave can reach?” instead, it should be “What’s the max temperature objects can reach in a microwave?”
The Maximum Temperature of Microwaved Objects
Unlike conventional ovens that have temperature settings, microwave ovens don’t have temperatures at all. The object will continue heating up until you turn off the appliance, the material changes state (e.g., from liquid to gas), or it gets destroyed.
So the maximum temperature is the one right before the object gets destroyed in the microwave. This temperature will vary from material to material because of the different thermal properties of objects.
But heating food is the most common use of microwaves. And most, if not all, foods have water in them. So the maximum temperature food can get to and still be edible is near 212°F (or 100°C), which is the boiling point of water. At this temperature, the water in the food turns to vapor and escapes. When all the water escapes, the food will likely start burning.
However, it’s possible to superheat water up to 248°F (or 120°C) in a microwave. But this will only happen if the water is pure, the container has no scratches, and it remains undisturbed in the microwave.
With superheated water, there’s a great risk of scalding when you pick the container. That’s why it’s advised to leave a wooden or plastic spoon in the water. The spoon will prevent superheating by disturbing the water’s surface and allowing it to boil at the normal boiling temperature.
What Affects the Temperature in a Microwave?
Cooking food in a microwave can be more energy efficient than using conventional cooking methods because the food cooks faster, and the heat affects only the food and not the container. And according to the FDA, microwave cooked food may be more nutritious than food cooked conventionally.
Like you know, temperature determines how quickly your food will cook. And in a microwave, how quickly you reach temperatures that are high enough to cook food depends on several factors like the size and shape of the food, how much water is present in it, the size of the food compartment, and the power and wattage of the appliance.
Size and Shape of the Food
Like in conventional ovens, large amounts of food take longer to heat up in a microwave because more molecules are vibrated. The shape also affects microwaving, as round shapes absorb microwaves better than ovals and rectangles.
The Amount of Water in the Food
Water molecules are one of the most affected by microwaves. So, foods like vegetables and fish with high water content will heat up faster than less moist foods.
Size of the Cooking Cavity
The size of the microwave cavity determines how many waves will hit the food and how often they’ll do so. An object in a large microwave will take longer to heat up, as it won’t get hit by as many waves as a similar object in a smaller appliance.
Power and Wattage of the Appliance
Wattage is the most critical factor that affects microwave cooking time. The wattage is based on the size of the Magnetron in the appliance, so bigger magnetrons have higher wattages, and higher wattages produce more microwaves to cook food faster.
Microwave wattages range from 500 to as high as 1,200. Anything lower than 700 is not ideal for cooking, as it will struggle to heat food evenly. A 1000 watt microwave will serve well for heating, cooking, and defrosting food as well.
Although microwaves can heat stuff quickly, the appliance itself doesn’t get hot like a regular oven. The heating is achieved by rapidly vibrating the water or fat molecules in the food using high-frequency microwaves.
The microwaves are produced by a Magnetron, a device in the appliance that converts electrical energy to microwaves. The waves then follow a tube to the cooking cavity, where they are absorbed by the food, triggering a vibration of the food molecules.
Since most foods contain water, the maximum temperature the food will reach and still remain edible will be 212°F (100°C), which is the boiling point of water. After this, the food will soon start burning.
The rate at which the food reaches this temperature will depend on the size and water content of the food, wattage of the appliance, and the microwave oven’s size.