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.