A new high-tech 'Pistachio Blaster' can separate high-value open-shell pistachios from lower-value closed-shell nuts by listening to the sound of each nut striking a steel block, the Agricultural Research Service has said.

The sorter, which has about 90% accuracy and sorts around 25 nuts per second, is designed to reduce losses caused when sorting machines make errors, misdirecting premium open-shell pistachios into bins of closed-shell nuts. Open-shell nuts typically make up about 78% of the US harvest.

The machine analyses sounds made during and immediately after each nut strikes a polished stainless steel block. The sounds, first captured as electrical signals by a precisely positioned directional microphone, are sent to a personal computer, where they are converted into digital data. The computer distinguishes the sound pattern made by the impact of a closed-shell pistachio from that of an open-shell nut and sends a signal that causes a blast of compressed air to direct closed-shell nuts to the reject bin.

The Blaster was developed by ARS agricultural engineer Thomas Pearson while at the agency's Western Regional Research Center in Albany, California. ARS is the US Department of Agriculture's chief scientific research agency.