The agricultural landscape in Puglia is characterized by the strong presence of the olive tree and, in the karst areas, by the so-called underground constructions linked to the production of oil: these are real oil mills, also called trappeti, from the Latin Trapetum or Trapetus.
The ingenuity of the peasants, struggling with adverse climatic conditions and pressured by the need to cope with periods of famine, has given concrete answers to two types of problems: avoiding the solidification of oil caused by low winter temperatures and equipping themselves with adequate structures to its processing without the economic burden of building a building.
Obtaining the mills by digging in tuffaceous or calcareous soils was the solution.
The oil, in fact, solidifies at 6 degrees. In the subsoil, however, the temperature is constant and higher also thanks to the large lights that burned day and night, and this allowed the oil to retain its natural fluidity, thus making it easier to extract, collect in the tanks and the deposit of impurities during the decanting phase.
But that's not all, the "trappetaries" knew well that building a building from scratch would almost always involve unsustainable costs, including skilled labor, purchase and transport of construction materials. Digging underground, on the other hand, required unskilled labor - therefore less expensive - and no use of construction materials.
The underground oil mills were built with this logic until the mid-eighteenth century and used, albeit sporadically, until the mid-twentieth century, spreading in particular in the Salento area.
Depending on the more or less complex structure, the underground oil mills are distinguished between vertical and horizontal but all have a system of machines consisting of a large circular stone mill, driven by a mule that turns in circles, a large press, a small and the various equipment necessary for the collection and storage of oil.
The underground oil mills were built with this logic until the mid-eighteenth century and used, albeit sporadically, until the mid-twentieth century, spreading in particular in the Salento area.
Depending on the more or less complex structure, the underground oil mills are distinguished between vertical and horizontal but all have a system of machines consisting of a large circular stone mill, driven by a mule that turns in circles, a large press, a small and the various equipment necessary for the collection and storage of oil.
In particular, the presses, mainly built with oak or olive wood, were of two types: "Genoese" and "Calabrese". The “Calabrese” press consisted of a large horizontal beam, called a “pancone”, crossed by two vertical threaded screws embedded in hard limestone plinths.
The "Genoese" press, so called due to its widespread use in Genoa and throughout Liguria, was instead introduced in Puglia in the early nineteenth century and had a more complex structure. Starting from the nineteenth century these structures were progressively abandoned to give way to modern oil mills, first semi-underground and then definitively built on the surface. Today it is still possible to visit what remains of these marvelous underground architectures, some of which retain, as well as the large stone millstones and collection tanks, the elementary decorations that embellish the walls carved into the rock, evocative of almost religious atmospheres that still linger in these places of ancient labors.
Among the best preserved underground oil mills, the Grottaglie mills, the “Lagopagliaro” mill in Ostuni, the “Granei” in Sternatia and the “Caffa” mill in Vernole certainly deserve a visit.
