The first essential step in bread-making was grinding the wheat with stone mills, followed by sifting to separate the flour from the bran. Despite the presence of many public bakeries in the Vesuvian cities, bread was still prepared at home, as evidenced by the discovery of numerous small hand mills.
With domestic mills, the flour obtained was not finely ground and contained many impurities such as siliceous granules, released from the abrasion of the lava stone elements. Analysis of bread remains from Herculaneum has shown that these siliceous elements were indeed present in the dough and, as a result, ingested by the inhabitants—this is confirmed by the significant dental wear found on the skeletons of those who took shelter in the boat sheds by the beach.
The specimen on display was found in the House of the Genius, a building largely explored between 1828 and 1850, located along Cardo III.
The structure is composed of a fixed cylindrical base, called the meta, with a conical-shaped top. Above it rests a second cylindrical block, called the catillus, hollowed in the center to form a double cone with opposing vertices—one pointing downward and the other upward. A central pin ensured rotation, while lateral holes on the catillus allowed the insertion of a rod to facilitate movement. The grain was poured in from the top and, once ground into flour, exited through the hollow between the two elements.