These are tropical fruits about the size of eggs, with a brownish purple skin that wrinkles when ripe. (There is also a yellow-skinned variety.) They are mostly hollow when ripe, with juice, seeds, and a little flesh inside. The tart juice has an intense, exotic flavor and aroma greatly prized by pastry chefs. Select fruits that are large and heavy for their size. If they are smooth, let ripen at room temperature until the skin is wrinkled.
To use, cut in half, taking care not to lose any juice. Scrape out the seeds, juice, and pulp. Seeds can be eaten, so do not discard. If you need only the juice, it is much more economical to buy the frozen juice, as fresh fruits are expensive.