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Melon Thumper
August 06, 1999
Double click the movie to stop it.

Few tastes remind one of summertime like a sweet succulent watermelon. But an unripe watermelon can dampen a summerís picnic like a thunderstorm. Fortunately, a group of students at the University of Delaware are developing a device to improve the odds of picking the perfect melon. And this is good news for the watermelon industry, which loses money annually by second-guessing the readiness of the crop for harvest.

"Growers have a real problem when there is a wide range of watermelons out there with different levels of ripeness," says Ed Kee, a University of Delaware professor who posed the watermelon project to the students. "And as harvesting crews go through, it is very difficult to determine which one is fully ripe."

The Tell-Tale Thump

"Historically, growers have either thumped the melon or they have cut it open," explains Kee. "Also, they can tell by the dead tendril, which is the part of the vine next to the melon. The watermelon, where it lays on the ground, will turn from a white to a creamy yellow color. Thatís another indication of ripeness. But none of those are foolproof. Thatís why weíre interested in improving the process."

The University of Delaware students pursued the centuries old melon thumping method, updating it for the 21rst Century. First they measured how much sugar a watermelon needs to taste sweet. Then they created a device that measures the amount of sugar in a watermelon using sound waves.

A watermelon is placed on the platform, where a weight thumps each watermelon with the same force and velocity. A microphone picks up the sound waves and transfers this information to a computer, where the frequency of the sound waves is analyzed. The amount of sugar in a watermelon affects the sound wave. Once the size and shape of the melon are taken into account, the device can predict whether it has enough sugar inside to be sweet and ripeóthus taking the mystery out of melons.

"The testing we are doing now is to correlate the frequency of those waves which are different in a ripe melon as compared to an unripe melon," explains Kee. "We are learning that the size and shape and whether a variety is seeded or seedless also makes some difference."

Economic Impact

image: NWPB

The watermelon industry produces over 1.5 trillion pounds of watermelon annually, primarily in China, Turkey, Iran, and the United States. And it is not at all unusual for a 40,000-pound truckload of watermelons to be rejected at market if only ten of them are green. This places a large economic burden on the farmer, who pays for the freight charges to and from the market and is left with a harvest that cannot be sold. Consequently, the commercial availability of the melon thumper (which is not quite ready to market) is certain to receive an "A" grade from farmers.

Melon Minutiae

  • It may be sweet, but itís not a fruit. Watermelons are vegetables related to cucumbers and gourds.
  • Egyptians decorated tombs with the watermelons more than 5,000 years ago.
  • China, Turkey and Iran are the top watermelon producing countries. China grows nearly 40,000,000,000 pounds of watermelon a year. The USA comes in fourth with a measly 4,500,000,000 pounds.
  • Watermelons are aptly named: Theyíre 92 percent water.

Elsewhere on the web:

University of Delaware Extension Service

Ed Kee at the University of Delaware

National Watermelon Promotion Board



produced by Rogene M. Eichler West


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