Why You Need to Be on the Lookout for Foaming, Exploding Watermelons This Summer

Sorry, but that watermelon has to go in the trash.

As far as fruits go, watermelons seem reasonably low-maintenance. You pick one out at the supermarket or produce stand, give it an obligatory thump on the side, and take it home with you. But if your picture-perfect melon starts to feel squishy instead of firm, has a suspicious odor, or starts, uh, literally foaming, it needs to be discarded. According to some experts, it could also be dangerous.

Some melon enthusiasts have reported that their whole melons are actually foaming from one or both sides, which isn’t entirely out of the ordinary. (Just search Reddit’s r/WTF subreddit to see several posts from people who have been freaked out by a foaming melon.)

According to the Bangor Daily News, bacteria can be introduced into a watermelon while growing on the vine. The bacteria combine with the sugars and yeast inside the melon and start the fermentation process. The foam — which seeps out of the melon through cracks in the rind — is a sign that fermentation is happening.

Related: 11 Watermelon Recipes to Make This Summer

Hotter temperatures can speed up this process or make it more prevalent, and that’s what’s happening this year. In the United States, watermelons are primarily grown in Arizona, California, Delaware, Florida, and Texas, and all of those states have seen higher-than-average temperatures.

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

Savoie added that the foaming was a sign of a “real food safety issue.” Watermelons that have started to foam should not be eaten, and she even warns against bringing them into your kitchen. Because the fermentation process produces gas, all of that internal pressure can cause the watermelon to explode — and even cutting into a watermelon that has started fermenting could be unsafe. On top of that, foods that have begun to ferment in unsafe or unsanitary conditions can also harbor some nasty bacteria and viruses, including botulism, E.coli, and salmonella.

If you have a whole, uncut watermelon, it’s advised that you store it in the refrigerator. Once it is cut, the open side should be covered with plastic — or with beeswax wrap, if you’re trying to be plastic-free — and any cut melon should be consumed within three days. The National Watermelon Promotion Board does not recommend freezing your melon, writing that freezing can cause the rind to break down, which “produces a mealy, mushy texture.”

Also, be sure to thoroughly wash the outside of the watermelon before slicing into it.

If you end up with a foaming melon, carefully remove it from your house and discard or compost it. And you might want to take a photo, just in case you feel like sharing it on Reddit later.

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