Nut Morphology and maturation
Pistachios, like grapes, grow in clusters. They are classified similarly to almonds, peaches, apricots, plums, and cherries, as drupes. This means that they are comprised of three parts: a hull, a shell, and a seed. The pistachio is the nut or seed, as is an almond; in the case of peaches and apricots, the seed is discarded and instead the hull is eaten. As pistachios age, the hull and shell begin to separate and shell splits. Not all pistachios are like this, and not all nuts will necessarily split – this depends on the variety, irrigation, climate, and weather conditions. Early splitting is also possible in all varieties, when the shell will split before separating from the hull. This is dangerous, as the unripe hull provides access to the kernel for undesirable aflatoxins like Aspergillus Flavus. An early, quick harvest is the best way to avoid this, as early splitters need time before such toxins can set in.