Can Thumping Help You Pick the Perfect Watermelon?

By Mary Hightower, U of A System Division of Agriculture

Fast facts

Stem, ground spot color, skin all provide clues
Webbing, or scar tissue, can be an indicator

You’ve seen them. Buyers thumping, listening, sniffing, lifting and peering, all in the quest for the perfect watermelon.

How do horticulture experts size up their watermelons?

Vic Ford, who heads up the agriculture and natural resources section of the Cooperative Extension Service, has developed some criteria over the years. After all, Ford spent many years as director of the Southwest Research and Extension Center in Hope, a city famous for watermelons and its annual celebration of the summer sensation.

Here are Ford’s factors:

Dryness of the stem.
Yellow to orange color of the bottom – called “the ground spot,” and
Darkness of the webbing. Webbing looks a little like tan or grayish/brownish scar tissue on a melon’s skin.

“If the melon has a green stem, white bottom and light webbing, it is not ripe,” Ford said. “I can’t hear the difference between a ripe and unripe watermelon by thumping.”

Matthew Bertucci, a research scientist for the University of Arkansas System Division of Agriculture running several watermelon demonstrations this summer, said that what he’s learned in the field, doesn’t always apply in the produce aisle.

He agreed with Ford, that “a well-developed ground spot of tan or yellow indicates that the melon stayed in the field long enough to fully ripen. That’s the part of the melon that is in contact with the ground prior to being picked.”

“I’ve got a good protocol for picking a ripe melon in the field, looking for dried tendrils, breakdown of the waxy layer, ridging along the stripes, and development of a distinct ground spot,” Bertucci said. “But I find it difficult to tell the quality of the melons at the grocery or at a farmer’s market.”

However, fruit left in the field too long or stored in direct sunlight can get sunscald, which will diminish quality.

“The tricky thing for me is that you can look for all the field indicators for ripeness, so you don’t accidentally get an underripe watermelon,” he said. “But they don’t tell you anything about storage quality or sweetness, so they won’t help if a fruit is overripe or a watermelon wasn’t stored properly. And no one is happy to get a mealy watermelon.”

Bertucci said there are researchers who measure watermelon quality with near-infrared imaging or by measuring its dielectric properties from outside the skin, but he takes a more direct approach: “In my experiments, we always just cut them open to check for quality directly.”

What about the acoustic qualities of the melon?

“As Dr. Ford said, thumping has never been helpful for me,” Bertucci said. “But I still do it. It’s a watermelon purchasing tradition.”

To learn more about the horticultural research and extension work being done by the Division of Agriculture, visit www.aaes.uark.edu and www.uaex.edu, or call your county extension office.