Bent low beneath a canopy of leathery green leaves in the sweltering heat of a Calabrian summer, Michele Cirelli is searching for a perfect fruit. Weaving his wrist through the inch-long thorns of his citrus trees, he picks out a good one—deep green and waxy. He takes it, gently, by its plump middle, careful not to damage its precious stem, and turns it slightly, so I might see how the light bounces off the knobbly ridges at its top. “This, this is the type the rabbis want,” he explains. A…