Sound solution to the pistachio problem
09:45 20 November 04
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Grab a handful of pistachio nuts and you will usually find several with shells that are closed so tightly they cannot be eaten. But soon you might be able to enjoy the snack without this frustration.
A gadget that listens to the distinctive pings made by nuts when they bounce off a surface could help to sort open-shell nuts from uncrackable closed ones.
Ripe, open-shelled pistachios, which fetch top dollar as a snack food, have to be separated from sealed unripe ones, which are normally shelled mechanically for use in ice cream or cake mixes.
But the spinning drums that producers use to do this are less than perfect. The inside of each drum has thousands of needles designed to catch on the open lips of ripe shells. Closed nuts end up in your nut bowl because sometimes they are speared too.
Blasted off
Now Tom Pearson, an engineer at the US Agricultural Research Service in Manhattan, Kansas, US, thinks he has the answer. He developed a sound-based sorter after noticing the different noises the two types of nut made when they struck the ground. “I could pick the types out perfectly without looking,” he says.
Pearson’s machine drops 25 nuts per second onto a steel plate, where a microphone picks up the impact sound they make. Signal-processing software detects the shorter ping of a closed-shell nut, and opens an air valve to blast it off the line.
While not as fast as the needle picker, the sound sorter is cheaper to maintain and up to 97% accurate – against the needle sorter’s 90%.
Geoff Gibbons of Setton Pistachio, California, is testing five sound sorters in tandem with his needle pickers. He estimates the machine will save the company $500,000 a year, and lot of frustrated customers.
Anna Gosline
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