Nothing heralds summertime and its star-spangled main event quite like a red, ripe, juicy watermelon. That is, unless your sweet, refreshing dessert should begin to spit, hiss and foam, and then go KABLOOEY, spurting putrid juices all over your picnic or – perish the thought – spewing mushy melon guts all over your kitchen or festive tablescape.
So just how obnoxious can one fruit be, you ask?
For the most part, you'll never meet a more pleasant snack than the watermelon. It's like the John Candy or Labrador retriever of fruits. But every now and then, like other things in life, you run into a bad one. And when you do, there's no need to freak out or disavow the Citrullus lanatus. Instead, be curious and amazed, as an exploding watermelon definitely makes for a really weird science story to tell your friends or, better yet, a jaw-dropping YouTube video:
So what's going on when a watermelon turns prankster and explodes?
Walter Reeves Weighs In
The garden guru of the Southeast, Walter Reeves, aka The Georgia Gardener, says in an email that what's going on is the process of fermentation.
"It's happening because the watermelon is full of sugar and a fast growing bacteria or fungus got in there somehow and it is fermenting. Maybe it got poked by something on the trip home or maybe it had an unnoticed blotch disease infection," he says.
"Fermentation causes many different chemicals to be produced. Some smell of alcohol, some smell of vinegar, some are floral, etc. Fermentation produces carbon dioxide gas, which hisses as it comes out of the rind under slight pressure. So the simple answer is that a watermelon can ferment inside and the pressure can cause various effects," says the retired radio and television host, author and weekly gardening columnist for the Atlanta Journal-Constitution.
Think the 'fizzes-like-crazy' sound a soda makes when you shake up the can before you open it.
Bacterial infection can be another reason why a watermelon splits.
"Bacterial blotch disease comes from infected seed and only affects the rind," says Reeves. "It does not spread into the interior. But if the blotch cracks, other bacteria and fungi can go through the cracks to the interior of the fruit and begin fermentation. If you find an infected watermelon with only a small blotch on the rind, the interior should be fine. But if the interior smells bad or seems watery, don't eat it."
Watermelons are more than 90 percent water. So what happens when a watermelon bursts?
"It expels fluid violently," says Reeves. Think mini volcanic eruption.
"Exploding," says Reeves, "can be caused by genetic factors that influence rind thickness, sugary pulp and small fruit size. Thin rind + super sweet pulp (which readily absorbs water) = BOOM! on a hot day."
The Exploding Watermelon Gene
So, is it true that there's an "exploding gene"?
Watermelon splitting or "exploding" can also be caused by the explosive rind gene which is found in many heirloom varieties. Dr. Penelope Perkins-Veazie, a plant physiologist and professor of horticulture at North Carolina State University (NCSU), says in an email that the explosive rind gene was identified back in 1937. Basically it causes the fruit rind to burst or split when cut.
"So a little bump will pop the rind open and the turgor pressure in the fruit pushes flesh far and wide," says Perkins-Veazie. "Triploid [or seedless] watermelons require diploid [seeded] pollinators, but usually growers don't want a lot of large seeded watermelons to harvest. So incorporating the explosive rind gene into the small fruited, seedy pollinator fruit means they can be stepped on, destroyed, but fruit are small enough (usually palm sized) so they won't squirt all over the seedless fruit."
Mark Twain once proclaimed the watermelon, "the chief of this world's luxuries, king by the grace of God over all the fruits of the earth. When one has tasted it, he knows what the angels eat."
Mark Twain must never have encountered what Walter Reeves describes as the "ooey-gooey, slimy, yucky puddle of crapola" left behind by a catastrophic watermelon rind failure. Otherwise, Twain's proclamation might have begun with, "What in tarnation?" and ended with "angel vomit."