This amount of foam bubbling out of a watermelon means the fruit inside is fermenting and it's not safe to eat. Left alone, it could also explode. Credit: Courtesy of Julie Raines

It was not exactly a ticking time bomb, but left alone, the foaming watermelon on Julie Raines’ kitchen counter could have become a fruity explosive device.

At best, the foam bubbling out of the melon created a sticky mess. At worst, it was a frothy indication of a serious food safety issue.

The foam emerging from Raines’ watermelon is a sign the fruit inside is actively fermenting — a natural process that started far from her Bowdoin kitchen. And it’s been affecting more watermelons this summer as the states in which the watermelons are grown have been facing above average temperatures.

Most of the watermelons found at Maine stores come from Florida, Arizona, California, Delaware or Texas.

At some point in the growing process in one of those states the melon picked up a bacteria. That bacteria combined with the natural sugars and yeast in the melon. Fermentation — the chemical breaking down of the melon’s insides — began.

“There have been increases in hot weather in those parts of the country,” said Kathy Savoie, professor and food safety expert at the University of Maine Cooperative Extension. “Fruits have a natural sugar called fructose and under extended and undesirable storage conditions, it will ferment.”

It’s also been unusually warm in Maine recently, increasing the likelihood of melons and other fruit fermenting here if not stored properly.

A watermelon that has started foaming or leaking liquid should never be consumed, Savoie said.

“The foaming indicates a real food safety issue,” Savoie said. “People should not knowingly bring it into their home and certainly not eat it.”

Once the fermentation begins inside a watermelon, it creates the perfect environment for toxic pathogens to flourish, including botulism, E. coli and Salmonella, according to the Fermentation Association.

If enough gas that is produced in the fermentation process builds up inside the fruit, it can cause the watermelon to explode. Cutting into a fermenting watermelon can also result in an explosion.

To avoid risk of fermentation, watermelons — as with any perishable fresh fruit — should be stored in the refrigerator once you bring it home, Savoie said.

All fruits — even ones with rinds like melons — should be washed thoroughly before cutting into them, she said. That’s because any harmful pathogens on the outside can get pulled into the edible inside from the knife’s slicing.

“I understand that watermelons are large and can be difficult to fit into the refrigerator,” Savoie said. “But especially once they have been pierced or sliced through the skin or rind, it’s the perfect opportunity for mold, yeast and bacteria to get on the food.”

Lack of refrigerator space is exactly how Raines’ watermelon ended up on her counter for several days.

Three days later the foam appeared, and closer inspection showed it was bubbling out of the watermelon.

“It was really creepy looking,” Raines said. “It was bubbling like soap.”

Unsure what to do, she placed the foaming fruit into a zip-close bag, put it in the refrigerator and wiped down her counter.

As a retired biology teacher from Yarmouth High School, Raines knows all about the fermentation process, but a foaming watermelon was a first for her.

She posted a photo and video of the melon in a Maine gardening group on Facebook on Tuesday asking if anyone else had experienced anything similar. By the next day, her post had racked up 161 comments, with many warning her to not eat the fruit and to secure it in case it blew up.

Others spoke of their own experiences this summer of buying watermelons around the state that showed signs of rot or fermentation when cut open.

The produce manager at the Hannafords on Broadway in Bangor said he’s never heard of watermelons foaming. He said he was not aware of any recent complaints of poor watermelon quality in Hannaford stores.

Now that she understands what is going on with her foaming watermelon, Raines is getting back into high school biology mode.

“I’m going to leave it out in the sun in my yard so it gets warm,” she said. “Then I am going to stand back wearing safety goggles and use a long knife to poke it to see if it explodes. I’m all about experimentation.”

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.