This is the fruit from P. vitifolia, I included an egg for comparison.
Red Passion Flower Fruit
Let the fruits fall on their own, or fall off with the slightest touch, then keep them until they get really wrinkled. I had to use a steak knife to cut them open, unlike the fruits of P. incarnata.
Very sour if fruits aren't wrinkled, somewhat insipid even after sitting around a few days.