Pistachio

choi

(1) Summary:
(a) pistachio
http://en.wikipedia.org/wiki/Pistachio
(Pistacia vera; a small tree originally from Persia (Iran); a desert plant; The fruit is a drupe)

(b) drupe
http://en.wikipedia.org/wiki/Drupe
(In botany, a drupe is a fruit in which an outer fleshy part (exocarp, or skin; and mesocarp, or flesh) surrounds a shell (the pit, stone or pyrene) of hardened endocarp with a seed inside; view the graphic of "a typical drupe (peach)": pericarp comprises exo-, meso- and endo- carp)

The combining forms from Greek: mes- is middle, and -carp (karpos in Greek), "part of a fruit or [the entire] fruit."
www.m-w.com  

(2) Mechanical harvesting: principle is the same
(a) Pistachio harvesting. YouTube.com, Uploaded by CoeOrchard on Mar 26, 2010.
http://www.youtube.com/watch?v=3c4rG94XQEQ&feature=related
("C7M shaker and L2 receiver Shaking Pistachios")
(b) Harvest of organic olives with mechanical vibration in Douro. YouTube.com, uploaded by QuevedoPortWine on Jan 13, 2009.
http://www.youtube.com/watch?v=JYzFqSFyTRM&feature=related

(3) I can not find a video clip showing how to mechanically shell pistachio.
(4) Various metods are applied to differentiate "early splits" from normal pistachio nuts (and nuts from shell, following mechanical shelling), such as electronic imaging, sound effect.

But why is it important to differentiate "early splits" from normal pistachio nuts.

In a nutshell, early splits may be contaminated with aflatoxin, a carcinogen, as well as cause shell staining and difficult shelling, resulting in shell adhesion or scratch of kernel (for aesthetic reasons)--similar to the observaton that American consumers won't buy bruised bananas.

To understand "early splits," one needs to know anatomy of a drupe (see above). In Pistachio, the hull (fleshy but less meaty than, say, a peach)) is mesocarp as well as exocarp whereas the shell, endocarp. (In comparison, in an orange, pulp, divided into segments, is mesocarp and the rind is exocarp. In a cherry, the skin and flesh (both of which we eat) are exo- and meso-carp, respectively.)

(a) Doster, M et al, California Agriculture 55: 28-31 (2001).
http://ucanr.org/repository/cao/ ... 28&fulltext=yes

Quote:

"Early-split nuts, which have both split hulls and shells, are frequently moldy and damaged by insects. In contrast, normal pistachio nuts can have a split shell but an intact hull.

"In the orchard, pistachio nuts typically split their shells, which are surrounded by a hull. Most nuts, however, do not split their surrounding hull and have an intact hull until after harvest. This distinguishes pistachio nuts from almonds and walnuts, which frequently rupture their hulls in the orchard but typically not the shells. Unfortunately, a small percentage of atypical pistachio nuts, known as 'early-split nuts,' rupture both their hulls and shells in the orchard, exposing the kernel to invasion by fungi and insects. An additional problem is that the rupture of the hull usually results in dark staining of the shell.

Caption of the last photo: "The normal developmental stages of pistachio nuts are stage 1, the developing shell increases in size, left; stage 2, shell hardens, middle; and stage 3, the kernel grows, the hull separates from the shell, and the shell splits, right.

(b) TC Pearson et al, Physical Properties of Pistachio Nuts. Transactions of the ASAE (American Society of Agricultural Engineers), 37: 913-918 (1994).
http://afrsweb.usda.gov/SP2UserFiles/Place/54300520/226 physical_properties_of_pistashios.pdf

Abstract: "The hulls of early split pistachos abnormally split open several weeks before harvest, making the kernel more vulnerable to the aflatoxin producing mold Aspergillus flavus. The most distinguishing features of early split pistachios nuts were found to be shell staining and hull adhesion tendencies.

Introduction: "Pistachio nuts are characterized by a split in the shell at the calyx end of the nut. This split normally occurs on the tree about a month before harvest. The hull (mesocarp) of pistachio usually encloses the shell and remains intact through harvest, serving as protection for the kernel. On normal nuts, there is space between the hull interior and shell exterior, so the shell can split open without splitting the hull. However, about 1 to 4% of teh time, the hull will adhere tightly to the shell and the hull will split open along with the shell. These nuts are called 'early splits.' The split in the hull allows an unobstructed passage to the kernelfor airborne mold spores and insects or other small animals, such as mites, that might be carrying mold spores.

Please take notice that "hull interior and shell exterior" still means hull outside the shell, with the inside of the hull separating from the outside of the shell.

(c) Ezzeddine Boutrif, Prevention of Aflatoxin in Pistachios. Food and Agriculture Organization (FAO), "Adapted from the author's presentation at the Pistachio '97 Conference, 27-28 October 1997, Rome, Italy."
http://www.fao.org/DOCREP/W9474T/W9474T06.HTM
("The shells of most pistachio nuts split naturally in the orchard prior to harvest. Fortunately, the hull covering the shell usually remains intact, protecting the kernel from invasion by moulds and insects (see Figure). Nuts that are poorly protected by hulls are most prone to contamination in the orchard. Sometimes the hull is attached to the shell so that it splits with the shell, exposing the kernel to moulds and insects.")