In early split pistachios the hull is still tightly bound to the shell, but has a narrow, blackish and gummy-looking premature split.

Typically the internal pistachio shell splits before harvest while the protective outer hull stays intact until after harvest. Early split nuts are when both the outer hull and internal shell split while still on the tree, exposing the kernel to invasion by insects and molds, including Aspergillus flavus which produces aflatoxins.
; Fresno County Credit: Themis J. Michailides
In early split pistachios the hull is still tightly bound to the shell, but has a narrow, blackish and gummy-looking premature split. Credit: Themis J. Michailides