Hong Kong police destroyed a German-made grenade from World War I on Saturday morning after the device cropped up in a shipment of imported potatoes at a local potato chip factory.

The grenade, described by authorities as having been caked with mud and dirt, was discovered by workers at a factory run by Japanese snack maker Calbee, South China Morning Post reported.

Police said they used a “high-pressure water firing technique” to safely detonate the weapon.