Milling consists in the very first phase of extraction. Here olives undergo mechanical actions leading to the break-up of their cell wall and membranes resulting in the spilling of oil and cell fluids. This action happens through the rubbing of pit fragments on pulps or as a result of the impact caused by mechanical devices rotating at high speeds on pulp masses. The product derived from this step in most plants is oil dough, a semi-fluid mass composed of a solid (pit fragments, peels and pulp) and a liquid (oil and water emulsion) part.
The systems used are basically of two types: Pressing, Separator.