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New effort to crack nutty problem

"Laughing pistachios" occur when the nut grows too big for the shell.
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(CNN) -- Munch your way through any packet of pistachio nuts and there will inevitably be a small pile of uncrackable shells left over.

But now an American agricultural engineer believes he has come up with a more efficient way of making sure only edible kernals make it into your packet.

And while that's good news for pistachio-philes, it promises to be very profitable for farmers as well, with less open shells being lost amid the lower-value closed nuts.

More than three-quarters of a typical harvest will be "laughing pistachios," the name given to the open nut when the shell cracks open in a wide smile revealing the green kernel within.

Yet the task of attempting to separate the remaining closed nuts is estimated to cost pistachio producers up to $7 million a year, largely because so many open nuts slip into the closed pile, from where nuts are shelled mechanically for use as flavoring for ice cream and cake mix.

Pistachios are currently sorted in spinning drums in which the open nuts are easily caught on hundreds of needles. Unfortunately closed nuts can often get snared as well.

But, with the "Pistachio Blaster," Thomas C. Pearson of the Kansas-based Agricultural Research Service claims to be able to segregate closed nuts from the rest with 90 percent accuracy.

The device is based on impact acoustics, with a computer able to tell whether a nut is open or closed simply by the sound it makes as it falls onto a stainless steel block.

"I could pick the types out perfectly without looking," Pearson told the New Scientist magazine.

When the computer recognizes the distinctive sound pattern of a closed nut, it triggers a blast of compressed air to shoot the nut into the rejects pile.

The technology is already in use at Setton Pistachio in California, the state which produces 98 percent of the U.S. pistachio harvest, with the company expecting to save up to $500,000 a year.

While slower than existing sorters, the Pistachio Blaster can still deal with 25 nuts per second and the device could also be adapted for processing other agricultural produce such as hazelnuts or wheat.

As for cracking open those tantalizing slightly split shells in the meantime, the California Pistachio Commission recommends using the shell of an already-opened nut to prise out the contents.

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