Another misconception is that microwave ovens cook food "from the inside out", meaning from the center of the entire mass of food outwards. This idea arises from heating behavior seen if an absorbent layer of water lies beneath a less absorbent drier layer at the surface of a food; in this case, the deposition of heat energy inside a food can exceed that on its surface. This can also occur if the inner layer has a lower heat capacity than the outer layer causing it to reach a higher temperature, or even if the inner layer is more thermally conductive than the outer layer making it feel hotter despite having a lower temperature. In most cases, however, with uniformly structured or reasonably homogenous food item, microwaves are absorbed in the outer layers of the item at a similar level to that of the inner layers. Depending on water content, the depth of initial heat deposition may be several centimetres or more with microwave ovens, in contrast to broiling/grilling (infrared) or convection heating—methods which deposit heat thinly at the food surface. Penetration depth of microwaves is dependent on food composition and the frequency, with lower microwave frequencies (longer wavelengths) penetrating further.[citation needed]
Compared to liquid water, microwave heating is less efficient on fats and sugars (which have a smaller molecular dipole moment).[31] Sugars and triglycerides (fats and oils) absorb microwaves due to the dipole moments of their hydroxyl groups or ester groups. However, due to the lower specific heat capacity of fats and oils and their higher vaporization temperature, they often attain much higher temperatures inside microwave ovens.[30] This can induce temperatures in oil or very fatty foods like bacon far above the boiling point of water, and high enough to induce some browning reactions, much in the manner of conventional broiling (UK: grilling), braising, or deep fat frying. Foods high in water content and with little oil rarely exceed the boiling temperature of water.
The second problem is due to food composition and geometry, and must be addressed by the cook, by arranging the food so that it absorbs energy evenly, and periodically testing and shielding any parts of the food that overheat. In some materials with low thermal conductivity, where dielectric constant increases with temperature, microwave heating can cause localized thermal runaway. Under certain conditions, glass can exhibit thermal runaway in a microwave to the point of melting.[41]
“What is microwave radiation? Is it dangerous? Are microwaves safe?” We see these questions a lot, so let’s clear it up once and for all: this type of electromagnetic radiation can be dangerous at high levels, but we’ve been using microwaves for decades, and it’s never been a problem. This is because, from the mesh door to the locking mechanism, microwaves are specifically sealed to prevent radiation from escaping, and the design works really, really well. However, if your oven door is damaged or if you think something is wrong, call a contractor and have them test radiation levels. It only takes a few seconds, and then you’ll know for sure.

However, lower-frequency dielectric heating, as described in the aforementioned patent, is (like induction heating) an electromagnetic heating effect, the result of the so-called near-field effects that exist in an electromagnetic cavity that is small compared with the wavelength of the electromagnetic field. This patent proposed radio frequency heating, at 10 to 20 megahertz (wavelength 30 to 15 meters, respectively).[5] Heating from microwaves that have a wavelength that is small relative to the cavity (as in a modern microwave oven) is due to "far-field" effects that are due to classical electromagnetic radiation that describes freely propagating light and microwaves suitably far from their source. Nevertheless, the primary heating effect of all types of electromagnetic fields at both radio and microwave frequencies occurs via the dielectric heating effect, as polarized molecules are affected by a rapidly alternating electric field.

The Quick Touch is a little expensive at $250. Amazon reviews also warn that the words printed on the buttons can wear off after years of use … but we actually liked the implication that this microwave will last long enough for some surface-level wear. If you’re going to pay more for an appliance it should be long-lasting and awe you with its usability and features — the Quick Touch did that for us.


It’s a rare compact model that comes equipped with 10 power levels, but this AmazonBasics model offers them. It also has Alexa voice control, which feels almost too futuristic for a microwave. You save on space without giving up much of anything with this model, which we call a solid win! This 0.7 cubic ft microwave is awesome and worth the counter space. The control panel is easy to use and laid out well.


The Breville’s accuracy and customizability were unmatched in testing. Because microwave heat conducts from the outside in, you’ll usually get rubbery edges if you don’t lower power to allow the heat to seep in further. But with the Breville, if something starts boiling over, you can use its power level and time dials in the midst of cooking and let the heat penetrate.
If you want a smaller microwave that still offers plenty of power, then this 1.1-cubic-feet, 1000-watt option from Samsung is a great pick. Customers love the modern black color scheme and the brushed stainless steel handle. The design of the control panel is also unique because it combines digital controls with a metal dial. The ceramic enamel interior is designed to wipe clean easily and resist grease, oil, and scratches. Online reviewers appreciate the unique LED display and say that one of the microwave's highlights is Eco mode, which allows you to turn the digital display off to conserve energy. One downside is that the microwave can be quite loud, according to current owners.
Water and other homogeneous liquids can superheat[54][55] when heated in a microwave oven in a container with a smooth surface. That is, the liquid reaches a temperature slightly above its normal boiling point without bubbles of vapour forming inside the liquid. The boiling process can start explosively when the liquid is disturbed, such as when the user takes hold of the container to remove it from the oven or while adding solid ingredients such as powdered creamer or sugar. This can result in spontaneous boiling (nucleation) which may be violent enough to eject the boiling liquid from the container and cause severe scalding.[56]
Water and other homogeneous liquids can superheat[54][55] when heated in a microwave oven in a container with a smooth surface. That is, the liquid reaches a temperature slightly above its normal boiling point without bubbles of vapour forming inside the liquid. The boiling process can start explosively when the liquid is disturbed, such as when the user takes hold of the container to remove it from the oven or while adding solid ingredients such as powdered creamer or sugar. This can result in spontaneous boiling (nucleation) which may be violent enough to eject the boiling liquid from the container and cause severe scalding.[56]
In 1945, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a chocolate bar he had in his pocket. The first food deliberately cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.[10][11] To verify his finding, Spencer created a high density electromagnetic field by feeding microwave power from a magnetron into a metal box from which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly. On 8 October 1945, Raytheon filed a United States patent application for Spencer's microwave cooking process, and an oven that heated food using microwave energy from a magnetron was soon placed in a Boston restaurant for testing.[12]
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