What’s With All the Foaming, Exploding Watermelons?

No, it doesn’t have to do with rubber bands.

Watermelons are a summertime staple to buy, cut, and eat. From the “thump test,” which involves knocking on the rind of the fruit to gauge ripeness, to the many ways someone can enjoy watermelon during the hot months, there’s a lot to know and love about these “green buddhas.”

And while summer is the prime time to eat watermelons, it is also the season that may cause this fruit to spoil, or ferment, faster. Now, fermentation is a great thing if we are talking about wine, kimchi, or cucumber pickles.

But when the process of fermentation starts within a watermelon, this means the fruit is spoiling...And probably foaming.

When these watermelons are still in the ground and growing, they can pick up bacteria. Once bacteria combine with the natural sugars and yeast in the melon—and other factors such as temperature come into play—the fruit can start to ferment.

Heat can speed up the fermentation process, leading to more foaming and exploding. According to the U.S. Department of Agriculture, about 80 percent of all watermelons are grown in four states—Florida, Georgia, Texas, and California. Other prominent states include Arizona and Delaware.

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

If the watermelons start to foam through the cracks of the rind, this is your clue that the inside of the fruit has begun to break down. In more concerning cases where a watermelon is seriously neglected, fermentation produces gas that builds up within the fruit which can cause the watermelon to explode.

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

So, if you see foam fizzing out of your watermelon, it is best to carefully dispose of it, no matter how much you want to make something delicious. Cutting into the fruit, even out of curiosity—because let’s be honest, the inside of a fermented watermelon sounds interesting—may not be safe and is best to be avoided. I'll save you your interest; it is only rotting fruit.

Watermelon belongs in the refrigerator—even an uncut, whole watermelon. This is the surest way to stop the fermentation process from starting during the hot summer months.

“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.”

When you cut into your watermelon and still have some left over, wrap the exposed side well in plastic, put it back in the fridge, and eat within one or two days.