Most coffee connoisseurs are familiar with the gentle hum of their favorite café’s grinder while they wait in eager anticipation of that aromatic first sip. But behind this everyday scene lies a surprisingly tricky problem. Coffee beans often come mixed with small stones—accidental stowaways from harvesting and processing. Nearly identical to beans in size, shape, and color, stones routinely evade even the most meticulous of inspections.

For cafés and commercial coffee producers, stray stones spell trouble. When they enter the grinding mechanism, they can severely damage the grinder’s precision-engineered cutting disks known as burrs. These burrs, essential but highly expensive, require expert alignment after replacement, which often disrupts operations and therefore imposes considerable downtime.

“Large-scale factories rely on advanced screening methods early in coffee production. Due to the size and cost constraints, these traditional screening methods aren’t practical for most busy cafés and smaller commercial settings,” said Dr. Teo Tee Hui from the Singapore University of Technology and Design (SUTD).