Geeky Girl's Guide to Watermelons

If you go to the grocery store and see a woman intently slapping all the watermelons like a watermelon-whisperer, then it's probably my mom. You might think she looks silly, but my mom *always* picks the sweetest and juiciest watermelon. How does she do it?

Unlike many fruits, watermelons stop ripening once they are plucked from the vine, so you want to find one that’s already ripe at the grocery store. These are three ways my mom tells if a watermelon is ripe without having to machete-y it open, but she mainly relies on the first way.

1. Slap the middle of the watermelon. Watermelon “meat” contains long chains of starches when they are young, but the starches break down into individual sugars as they ripen and age. The more “free-flowing” sugars give the meat a more jiggly feel. When you slap the melon, you want to feel and hear this jiggle. If you hear a dull thud like slapping a table top, the melon is unripe. If you hear and feel a reverberating “thump,” as if you’ve struck a gong, it is likely sweet and juicy.

2. Check the watermelon’s “field spot,” the part of the melon in contact with the ground during growth. If it is white, the melon is unripe. Instead, look for a creamy yellow to orangish color.

3. Check for any brown webbing on the rind. When bees pollinate the watermelon flower, it scars the membrane of the flower that eventually grows into the watermelon fruit. The more webbing, the more pollination, the sweeter.

You can also tell the flavor profile of the watermelon by its shape. Longer and skinnier watermelons are watery while ball-like watermelons are sweeter. And did you know you can buy square and heart-shaped watermelons? In Japan, farmers have figured out that encasing a young watermelon with a glass mold will shape the melon as it matures. Square watermelons can be more efficiently stacked and stored than round watermelons.

How are seedless watermelons made?

A seedless watermelon is sterile and incapable of reproducing seeds because it has an abnormal number of chromosomes. Chromosomes are bundles of genes necessary in reproduction. For example, you get half your chromosomes from your mother and half from your father. Because chromosomes code everything from your assigned gender to normal cellular functioning, an incorrect number of chromosomes can cause sterility. Similar to how a sterile mule is the offspring between a regular horse and donkey, a seedless watermelon is the offspring of certain watermelon pollen and flowers.

A standard watermelon flower contains 22 chromosomes, and its pollen contains half that, so 11 chromosomes. Let’s call this the watermelon dad. The watermelon mom has been chemically treated so that she has 44 chromosomes. The mom’s ovule cells therefore have half that, so 22. Crossing the mom’s ovule cell (22 chromosomes) and dad’s pollen (11 chromosomes) results in a watermelon with 22+11=33 chromosome, a melon that lacks the genetic code to produce viable seeds. Thus, a seedless watermelon.

So if you ever wondered how seedless watermelon reproduced to make more seedless watermelons, the answer is they don’t at all. Seedless watermelons have to continuously be bred. Pretty cool, huh? The next time you go to the grocery store, maybe you’ll become a skilled, knowledgeable watermelon whisper now too!