With a name like “Passion Fruit” you would think of some fabled fruit that is picked from lush green trees in a glorious oasis overlooking oceans or mountains, or both. The truth of it is that most passion fruits look like big tree seeds with soft gooey centers. The outer skin is a bit rough and fairly thick.
Because of this, it’s tough to know when passion fruits are ripe just from the look or touch. There are also varieties that have no wrinkles at all, perfectly round and red with the smoothness of a baseball but the squish of a tennis ball.
Once you cut through the thick skin you will be greeted by lots of juice from membranes that surround the crunchy, black seeds; the seeds don’t have much flavor but are edible. I suggest eating them, if only to make it less messy than trying to eat around them. They are a bit smaller than, and not as thick as, watermelon seeds.
In US markets, the purple, wrinkly passion fruit is usually the only one available. In Asia I’ve seen 3 different versions: purple, yellow and red. The purple tends to be the sweetest while the yellow has the most tang (acidity).
A final interesting note is that, per Wikipedia, the purple passion fruit is found to contain traces of cyanogenic glycosides, a derivative of the cyanide family. Passion indeed!