concentric stones mill
The shape of this concentric stones mill, allowed to crush olives without braking the bones. There have found remains in excavations together with remains of the olearia millstone, makes us suppose that in some antique exploitations first oil was elaborated without crushing of the bone, as they considered that bones damaged the quality of the oil and then they made the second crushing to break the bone in the olearia millstone.
This mill consists of a ring shaped stone that turns on a vertical stone with cylindrical-conical and fluted form. The separation between them was placed to make olives to friction between them without breaking the bones. The exterior ring stone was resting on the top part of the central millstone that at the same time was resting on a circular stone with parapet that was collecting crashed paste.
We have found remains of this kind of millstone in the North of Africa and in the Guadalquivir valley, giving a appearance date around the III century b.C
Concentric stones mill, used to crush olives without braking the bone
Source: Pieralisi España S.L