When a pistachio is ripened perfectly, its light-tan
shell splits open, revealing a rich-tasting, lime-green kernel that's
ready to roast and enjoy. This handy split-shell feature makes it easy
for you to loosen the plump nut from its protective housing.
Nicknamed "laughing pistachios" because they
look like they're smiling at you, open-shell nuts typically make up
about 78 percent of the U.S.-grown harvest.
But some of the remaining harvest is made up of closed-shell
nuts that cost pistachio processors an estimated $3 million to $7 million
in losses every year. That's due, in part, to sorting-equipment errors
that misdirect premium, open-shell pistachios into bins of lower-value,
To help solve this problem, ARS
agricultural engineer Thomas C. Pearson has invented the Pistachio Blaster
(see diagram below), a high-tech sorter that quickly segregates closed-shell
nuts from their high-value, open-shell counterparts with about 90 percent
accuracy. The Blaster doesn't damage the nuts, performs at the respectable
speed of about 25 nuts per second, and can pay for itself in less than
a year, Pearson says.
This super-sorter might be used to sort other crops, such
as hazelnuts, also called filberts, and wheat, notes Pearson. He developed
it while at the ARS Western Regional Research Center in Albany, California,
and is now with the agency's Grain Marketing and Production Research
Center in Manhattan, Kansas.
The Blaster relies on what's known as "impact acoustics"
to correctly sort the nuts. In a sequence of steps that occur faster
than the blink of an eye, the Blaster analyzes sounds made during and
immediately after each nut strikes a polished stainless steel block.
Those sounds, first captured as electrical signals by
a precisely positioned directional microphone, are sped to a personal
computer, where they are converted into digital datasome 350 pieces
of information, or data points, for each nut.
The computer distinguishes the distinctive sound pattern
made by the impact of a closed-shell pistachio from that of an open-shell
nut, "much like your ear can distinguish a 'plink' from a 'plunk,'"
Pearson says. When the analysis reveals the telltale sounds of a closed-shell
nut's bounce, the computer sends a signal that causes a blast of compressed
air to direct the nut to the reject bin.
One of the nation's largest pistachio processors, Setton
Pistachio of Terra Bella, California, holds a license for the Blaster,
and is already using several of these novel machines to make sure that
more laughing-face pistachios make their way from orchards to you.By
Agricultural Research Service Information Staff.
This research is part of Quality and Utilization of
Agricultural Products, an ARS National Program (#306) described on the
World Wide Web at www.nps.ars.usda.gov.
For further information on U.S. Patent No. 6,541,725,
"Acoustical Apparatus and Method for Sorting Objects," contact
Thomas C. Pearson, USDA-ARS
Grain Marketing and Production Research
Center, 1515 College Ave., Manhattan, KS 66502; phone (785) 776-2729,
fax (785) 776-2789.
"Pistachio Blaster" Finds Perfect Nuts" was published
in the November
2004 issue of Agricultural Research magazine.