You can tell if a watermelon is getting rancid by its appearance. If it’s discolored, mushy, or smells bad, it’s time to throw it out. The skin should have a bright color, and the flesh should be free of any blemishes. If a watermelon has a strong, foul odor, throw it out.
There are also some warning signs to look for. If a watermelon’s flesh is soft and mushy, it’s time to toss it. A tangy, sour, or foul-smelling smell is another sign, and it’s also past its storage time.