December 4

Why Do Grapes Spark in the Microwave? | A Detailed Explanation of What Happens


Author: Cornelia Suehr and its partners may earn a commission if you purchase a product through one of our links.

Why do grapes spark in the microwave is a question that rarely leaves the mind of curious science lovers who want to discover the science behind the mystery.

If you want to make some plasma at home, you need grapes and a microwave oven (see also convection microwaves). The effect of putting the grapes in the microwave is spectacular, but sometimes it ends up being a messy kitchen fireworks display. That is why you should be careful with the experiment as it may end up destroying your oven.

One of the explanations for this is that the grapes trap the energy that the microwave oven emits since the waves are the same size as the diameter of the grapes.

Why Do Grapes Spark in the Microwave Oven?

In 1995, Aaron Slepkov, a Trent University physicist, came across detailed information explaining the plasma making process using a microwave oven. The young physicist was fascinated by the method and kept it at the back of his mind. Aaron Slepkov, Pablo Bianucci, and Hamza Khattak, an undergraduate student, are co authors in a paper in the National Academy of Sciences of the United States of America.

Slepkov discovered the grape-in-microwave trick, in which a slice of grape erupts into a fireball of plasma. It also produces an ionized gas available in large quantities in the sun, among other places.

Purple grapes

Making plasma using grapes and a microwave requires a simple recipe: first, cut the grape in half so you can end up with two grape halves. The two halves are attached to each other at the end using a particular skin bridge. Heat the two halves of the grape for a few seconds, and a fireball erupts, consisting of electrically charged atoms known as ions and electrons.

The hot mix of electrically charged atoms (ions) and electrons is called plasma. The trick has been available online for decades. Some people thought that the eruption was due to the skin connecting the two grape halves. However, that is not true as two grapes put in the same bowl will behave the same. The same applies to two hydrogel beads, two quail eggs, or two ground cherries.

The study can help form a better understanding of nanoplasmonics. For instance, if you place two metal nanoparticles together, you get an enhanced electromagnetic field. But for metals, you see the field with light, as explained in this post, and not with microwaves.

Researchers say that grapes are the resonators for microwave radiation. That means they trap electromagnetic energy. The microwaves will bounce in the grapes for a while. The energy will then break down in a flash. The heat then forms a hot spot at the center of the sliced grapes due to thermal imaging.

Suppose you put two whole grapes next to each other in the microwave, the hot spot due to the trapped energy forms where the two grapes touch each other. The salts within the skin of the grape skin become ionized or electrically charged. This leads to the release of salt ions that produce the plasma sparks.

Empty white microwave

Is It Safe to Put Your Grapes in a Microwave Oven?

Should you microwave grapes? You can do so much using grapes, including freezing them into a healthy snack, making jellies and jams, and baking grapes into pies. You can also use grapes to prepare savory dishes, including red snapper and pork.

However, there's one thing that you shouldn't do with grapes. You should never put your grapes in a microwave. The caution has nothing to do with the taste of the grapes, but it has everything to do with safety.

If you put grapes in the microwave and then heat them, you'll see the grapes spark. Why does it happen like that?

A team of physicists combining thermal imaging, videography, and computer simulations, the team established that the grape sparks are due to the microwaves trapped in the grape. The hemispheres of the grapes act as spheres of water, which minimizes the wavelengths of the microwaves.

If you microwave the grape as one whole, the grape will trap the microwaves at its center. If you slice the grape into two slices and place the two pieces close to each other, the trapped microwaves will hop from one half of the grape to the next, forming an electromagnetic field. The electromagnetic field ionizes the sodium and potassium ions in the grape, resulting in a fire.

According to the team of physicists, there is no need to leave a skin bridge between the grapes you slice. Using two slices of grapes or using two whole ones offers the same results.

Red grapes on a white background

Do Grapes Explode While in the Microwave? 

One of the most intriguing questions that researchers have to grapple with is whether grapes explode if you heat them in a microwave.

If you cut a grape into two slices, put the halves in a microwave, and start heating, the halves will soon explode into a fireball that can badly damage your microwave and get you on a hunt for a new one (see retro-designed microwave ovens).

Some theories and hypotheses were used at the time to explain the phenomenon. One hypothesis was that the two halves of grapes form some form of antenna that directs microwaves across the skin bridge.

The real cause of the explosion is even more easy to understand.

When you slice the grapes into two halves, put them in the microwave, and heat them, microwaves will enter the grapes. When the microwaves enter the grapes, they form hot spots at the points where the two halves of the grapes are closest to each other.

The hot spots will become hotter as the microwaves continue to heat the grapes. The electrolytes surrounding the hot spots will become supercharged and form a plasma, an electrically charged or ionized gas that bursts into a fire. This method of forming an electrically charged or ionized gas is not unique to grapes. You can also use water-filled balls or other fruits of the same size.

Exploded food in a microwave

Some people slice the grapes into two halves when carrying out the experiment but leave a small skin connecting the two. The belief is that the skin acts as an antenna that connects the microwaves between the two halves. However, there is no need for a physical connection between the two halves of the grapes. You also don't need a physical connection if you are using two whole grapes.

Since an electric charge drives the bond, all you need to do is to ensure the fruits are close enough to each other.

What Foods Shouldn't You Put in a Microwave?

Apart from grapes, are there any other types of foods that you shouldn't put in your microwave?

If you are in a hurry, a microwave can come out as a worthy kitchen appliance as it helps you warm your food fast. On a side note, a microwave with 900 watts would suffice for basic heating, while for more demanding processes one should go with more powerful oven with 1100 Watts. To get back on topic, microwaves are versatile kitchen appliances that you can even use to cook whole meals if you have the skills. However, there are some types of foods that you shouldn't put in a microwave as they can destroy the microwave. Such types of foods include:

Hard-Boiled Eggs 

If you put hard-boiled eggs in a microwave, they will explode. As you microwave the boiled egg, hot steam builds inside it. The steam will release when you break the egg. You can deal with the problem by cutting the hard-boiled eggs before putting them in the microwave. This will prevent the hot steam from building up.

Eggs in a microwave


One reason you may not microwave some types of foods is because of safety reasons. However, you can choose not to put some types of foods in the microwave because of how they'll taste. A good example is bread.

Bread will not explode if you microwave it. However, it will not have a pleasant taste. Putting the bread in the microwave heats it from the inside out, which makes you miss the crunchy exterior you enjoy when you toast the bread. Microwaving bread also gives it a chewy and soft texture.

Spicy Peppers 

Although you may like your saucy peppers hot, you may not want them to catch fire. If you put hot peppers in the microwave, they will catch fire. Additionally, when you microwave spicy peppers, they release capsaicin molecules in the air. The molecules can be unpleasant to the eyes.

Frozen Meat 

As you might have already noticed, if you microwave frozen meat, some parts of the meat will remain cold while others become hot. The uneven distribution of heat is the reason why you shouldn't microwave frozen meat. Apart from being inconvenient, the uneven heat distribution can also encourage bacteria growth on the meat unless you cook it immediately.
Frozen meat


Should you put grapes in the microwave? Why do grapes spark when you microwave them? When you microwave the grapes, they generate so much energy that they explode into a fireball. The fireball can be large enough to destroy your microwave which may lead to you needing a new one. Fortunately, we already shared our thoughts on microwaves under 200 dollars. At the same time, though, because most sought-for microwaves come around this price range, you could get a great microwave for less than150 bucks, as well. Now to conclude this post, you must be aware that the energy generation happens if you slice the grapes into two halves or put two whole grapes in the microwave. Thus, it will be best to avoid microwaving grapes.

About the author

Cornelia Suehr

A professional chef and a passionate writer on all topics related to cooking, baking, appliances and kitchenware. Her posts resonate with foodies, home chefs and professionals.


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