You've got to know when to hold 'em and when to fold 'em ('em being watermelons)
As the weather gets swelteringly hot, watermelon begins to make up about 80 percent of my diet. While some folks will buy a whole watermelon at the grocery store and break down the fruit themselves, others are far more likely to buy it pre-sliced. Is it easier? Absolutely. But, like all produce, once it’s sliced open it will go bad much quicker. But while apple slices will go brown and grapes begin to wrinkle, watermelon doesn’t show its age the same way.
When selecting a whole melon at the grocery store, you want to check and make sure it’s ripe enough, but you also want to avoid a melon that’s overripe. The easiest way to tell is to check the skin for any soggy spots and patches of greenish-blue, black, or white mold.
Even if the exterior looks OK, there’s a chance that the fruit could have gone bad. If the flesh has noticeable dark spots or is covered in anything slimey, you should toss it. If it looks fine but has a sour or ~off~ smell, that’s another indication that this watermelon is no good. On the plus side, I bet if you can prove that you purchased rancid fruit and then take it back to the store immidiately (and make an appropriate fuss) you can get your money back.
Pre-cut watermelon packages tend to be tagged with an expiration date, and that should be taken seriously. Of course, most foods aren’t guaranteed to spoil by that date, so it’s best to know what to look for. Again, you want to avoid melon that's slimy, discolored, weird-smelling, or growing anything fuzzy.
Sometimes spoiled watermelon looks and smells fine. This is often the case with cut melon that’s been sitting in a container in your fridge for a week or so. Though the sealed container has prevented the fruit from getting slimy or growing mold, the melon can still be bad, and could potentially make you sick. If you take a bite and the fruit is sour or fizzy, spit it out and chuck the rest.
A good rule of thumb is to eat pre-cut watermelon by the expiration date, or at the most, within five days of buying the fruit. Watermelon you cut yourself and store in an airtight container in the fridge should also be eaten within five days. A whole watermelon can last in your kitchen for about a week (though if it’s really warm in your place, that may be too long, as our Senior Food and Drinks Editor Kat Kinsman found out last summer), and in the fridge for about two weeks. But really, why would you ever wait 14 whole days to slice into that melon?