Can you see any olive tree around you? Neither can we, but we can imagine that there were cultivated here in Valdorba at that time. We now it thanks to the remains of this medieval stone olive oil press, which stopped being used in the 18th century.
This is the area where the olives were received, cleaned and stored.
Olives are piled up and increase their temperature due to respiration. Thus, they start releasing water, which facilitates oil extraction.
The millstone grinds the olives placed over the lower millstone. The millstone is horse-powered. Thus the olive paste is obtained and then collected from the outer part of the lower millstone.
This lower millstone differs from the rest, as it has two parts: an outer part made of sandstone from the press, and another part made of conglomerate taken from a nearby area.
The paste is mixed with hot water in order to facilitate oil extraction and then it is distributed uniformly and piled up in big baskets made of esparto grass.
The pile of baskets is pressed for several hours; each group of baskets is pressed several times.
The result is a mixture of oil and olive mill wastewater (the so-called "alpechín").
The product resulting from the first pressings is collected with pitchers and kept in large earthenware jars, where the liquid rests until virgin olive oil separates from olive mill wastewater.
The product resulting from the last pressing is taken to the decantation tanks. The oil is less dense and comes out through the upper channel, while the wastewater is taken to a ditch or septic tank. This crude olive oil was used as fuel for altar lamps and for making soap.
After pressing, the marc (skin and pits) remains in the baskets, and is used as fuel or animal food.
This system is based on the lever principle. At first the beam rests in the dowel, which is slightly leaned towards the screw. The head of the beam rests in the top of the pile of baskets, which is higher than the dowel. The dowel is removed and several planks are laid for them to transmit the thrust to the baskets. Then, the shafts make the screw turn until the stone weight is lifted a meter approximately. The handles of the screw are tied to the beam. The stone weight slowly descends over the baskets and little by little the liquid pours into the channels and is conducted to the decantation tanks. The process was controlled by the beam master, who was responsible for the perfect functioning of the press and prevented changes in the trajectory of the beam.
It consists of a wooden structure fitted in the rock. A person has to screw the crossbeam down the screw in order to press the pile of baskets. This type of press was used before the lever-and-screw press.
