When watermelon is ripe, the green rind is firm and the pink flesh is sweet, moist and crisp. However, when a watermelon is overripe, the flesh begins to deteriorate and lose its flavor and consistency. A series of tests to determine ripeness can help you select fruit from the market or decide whether to discard a watermelon you already have on hand.
Press your thumbs firmly into the exterior rind of the watermelon. If there is a slight give beneath your thumbs, there is a high chance the watermelon is overripe.
Tap your closed fist on the exterior of a whole watermelon and listen for the sound it makes. Overripe watermelons have a dull and hollow sound.
Slice the watermelon in half with a sharp knife and check the interior. If the pink flesh looks grainy or deteriorated in any way, the watermelon is overripe. In the store, use this method to check precut melons for ripeness.
Press your fingertip into the flesh of the watermelon. If your finger sinks in with no resistance, the watermelon is likely overripe.
Try a bite of the watermelon. An overripe watermelon will feel mushy or grainy in your mouth with a slight bitterness.