There is provided an apparatus for splitting closed pistachio nuts in a controlled manner such that the longitudinal sutures of the nuts will be cracked open. The apparatus includes a cylindrical housing with a mandrel mounted for rotation therein to provide an annulus into which nuts can be introduced. According to various features of the apparatus, the pistachio nuts are rotated, oriented and then split along their sutures in the annulus and subsequently discharged through an opening in the housing. There is also provided a continuous process of treating closed shell pistachio nuts which includes the step of removing the denser foreign particles from the closed shell nuts by flotation; and a soaking step so that the shells of the unopened pistachio nuts will be saturated with water to provide a degree of shell flexibility such that when pressure is applied to the suture of the shell to effect splitting, the shell will flex rather than crack. The shells are subsequently surface dried and then introduced to a splitting operation of the type carried out by the apparatus previously described.