2019-03-12 Why Microwaved Grapes Shoot Sparks

We love food science because it helps us make better barbecue. And because it's cool. Take exploding grapes, for example. What? You never fired up a grape? Cut a grape in half, leave the halves attached, and stick the grape in the microwave oven. Press start and soon the grape will shoot out sparks or flames. Cool trick, huh? But what's going here?

Scientists recently studied the phenomenon to find out. Experiments show that the sparks are not caused by the conduction of electricity. They are caused by microwaves trapped inside each grape. Here's how. A single microwave wavelength measures about 5 inches long. But water inside the grape compresses the microwave wavelength to about 1/2 inch, about the thickness of a grape. Now, with a whole grape, the compressed microwaves bounce around inside the grape and concentrate in the center. With a single grape cut in half with the halves still touching (or with two grapes touching each other), the microwaves concentrate at the spot where the two meet. At that spot, a strong electromagnetic field creates a plasma, which is a superheated gas in which electrons have been stripped from the molecules. Plasma is the same thing that emits light in a plasma TV. In the grape example, the electromagnetic field sparks a plasma by stripping an electron from a sodium or potassium molecule in the grape. That spark triggers reactions in other atoms in the air, which lose electrons as they absorb the microwaves inside the oven. Poof! You get a spark.  

Interestingly, in the hotspot where the grapes touch, scientists determined that microwaves were 80 times smaller than the microwaves are in air. That means it's the water inside the grape that's causing the microwaves to concentrate. What if substances other than water could concentrate microwaves in a similar way, or concentrate them even further? That's the interesting part, and it has many scientific possibilities. Another interesting thing: most food consists primarily of water. What else can we fire up in the microwave? Check out an explosive grape video here.

grapes emitting sparks in microwave oven


Many merchants pay us a small referral fee when you click our links and purchase from them. On Amazon it works on everything from grills to diapers, they never tell us what you bought, and it has zero impact on the price you pay, but has a major impact on our ability to improve this site! And remember, we only recommend products we love. If you like AmazingRibs.com, please save this link and use it every time you go to Amazonhttps://tinyurl.com/amazingribs

...some HTML for the first variant...



Get Smoke Signals, our free e-letter. No spam. Guaranteed

Enter your email:

If you love barbecue and grilling you do our FREE 30-day membership in our Pitmaster Club. We can up your game.

  • FREE 30 day trial membership.
  • Sneak previews of Meathead’s new book.
  • We block ads from members.
  • Real community. No politics. No flame wars.
  • Monthly newsletter.
  • Video seminars with famous pitmasters.
  • Weekly podcasts with Greg Rempe.
  • Weekly BBQ cartoons by Jerry King.
  • Comprehensive Temperature Guide Magnet ($10 retail).
  • Monthly giveaways of Gold Medal grills and smokers worth up to $2000.
  • Discounts on products we love.
  • Support for AmazingRibs.com!

Post comments and questions below


1) Please try the table of contents or the search box at the top of every page before you ask for help.

2) Try to post your question to the appropriate page.

3) Tell us everything we need to know to help such as the type of cooker and thermometer. Dial thermometers are often off by as much as 50°F so if you are not using a good digital thermometer we probably can't help you with time and temp questions. Please read this article about thermometers.

4) If you are a member of the Pitmaster Club, your comments login is probably different.

5) Posts with links in them may not appear immediately.


Click to ask questions and make comments