Fostering curiosity in kids (and their parents) since 2011

“Why is a watermelon red inside?”

photo of cut open watermelons, showing their red insides and the occasional black seed

Photo via Good Free Photos

My daughter is a watermelon fiend. Given the option, she would eat nothing but watermelon at every meal. In the midst of a recent watermelon binge, my daughter paused long enough to spit out a question along with a black seed.

“Why are watermelons red inside, Mommyo?”

In an effort to curb parental addiction to our devices, we don’t allow iPhones at mealtimes.

I didn’t know, so my daughter graciously granted me an iPhone exemption so that I could find out.

Turns out ripe watermelons get their red color from lycopene, the same stuff that makes tomatoes red and carrots orange.

And though strawberries and cherries are also red, lycopene isn’t to blame for that. Strawberries and cherries get their lush red hues from anthocyanins, which when mixed with the increasing sugar in the ripening strawberry and cherry fruits turns the fruit red. Interestingly, the same stuff mixes with sugar in the more alkaline blueberry to turn the berries a distinctive blue.

Sound familiar? It should. Anthocyanins are used to make everyone’s favorite chemistry tool — litmus paper.

“Are watermelons always red, even the ones that aren’t ripe?”

No. Even though the lycopene that will turn the watermelon red is present in the fruit the entire time it is ripening, the insides of an unripe watermelon most likely won’t be red.

That’s because when the fruit is ripening, green chlorophyll masks the red color of the lycopene (or in the case of berries, the red/blue tones of anthocyanin) chemicals.

Chlorophyll’s annual self-destruction is the same reason leaves turn from green to red, gold, and brown in the fall.

When the growing season is over and the chlorophyll is no longer needed, the chlorophyll chemicals break up and disappear, allowing the colors of the other chemicals in the fruit (and leaves) of the plant to show through.

“What else about watermelons, Mommyo?”

Watermelons aren’t always red. I hear they can come in yellow, orange, and white as well, although I’ve personally never seen it.

9 Responses to ““Why is a watermelon red inside?””

  1. Strawberry Steve

    What a nice blog you have! Really cute! 😀
    By the way, I’ve tasted a yellow watermelon. As I recall, it’s flavor was very similar to a red melon, but was a bit milder and sweeter. Very delicious! :9

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    • shalahowell

      Thanks, Steve. By the time I discovered yellow watermelons existed, the season was over. I’ll have to hunt one down next year. They sound delicious. 🙂

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  2. Schmadeke

    Thanks for a great explanation. Would anyone happen to know what the lycopene reacts with inside the cell to create the red color?

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    • Shala Howell

      As far as I can tell, the lycopene is itself red, due to its inherent cell structure. The more double carbon-carbon bonds inside a carotenoid like lycopene, the redder it is. As I understand it, in an unripe watermelon, the lycopene is always red, but its red color is masked by the more powerful chlorophyll green. As the chlorophyll fades, the lycopene red comes out. I’m no chemist, though. So if you want to dive into a more detailed explanation, I can merely point you to the “Properties” section of the Wikipedia page for Carotenoids: https://en.wikipedia.org/wiki/Carotenoid

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  3. ROSE

    I BOUGHT A WATERMELON. TNSIDE OF IT WAS ORANGE.THE FIRST TIME SEEN THATCOLOR WATERMELON. IS THIS SAFE TO EAT JUST ASKING.

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    Reply
    • Shala Howell

      Hi there, the last watermelon I bought ended up being orange inside too. We ate it anyway and appear to have survived. I’m certain this comment comes too late to help you, but there it is. Hope you had a great summer, and thanks for visiting Caterpickles!

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