Process of extracting the olive oil, milling

The purpose of milling is to break down the cells of the pulp (70%) and stone (30%) which contain the oil to be extracted.

When the oil is green, at the beginning of the harvest, the cells containing the oil are smaller and the grinding size must be finer. As the olives ripen, the cells become bigger and hence the grinding size can be larger.

The finer the milling, the more “fines” (impurities) are in the oil.

Milling in the stone mill

The mill itself is made up of two cylindrical grinders of granite stone. This type of mill is a combination of tradition and technology.

The cylinders are grooved and their distance of separation may be graduated in accordance with the required grinding size of the stone and pulp.

The conveyor belt drops the olives in between the stones which, with one turning against the other, break up the pulp and the stone to extract the oil. This method of grinding the olives has the advantage of not stressing the olive, and the temperature does not, therefore, increase too much at this point of production.

These fragments then pass through some toothed wheels where the grinding size can be adjusted.

The resulting paste arrives at the beater via an endless screw.

Milling in the hammer mill

This mill is a stainless steel dual drum, the inside of which comprises two concentric sieves, with the “hammers” being positioned inside of these in the form of a helix. The hammers crush the olives and, if this process is performed at too high a speed, the action stresses the olive and increases the temperature at this point.

The hammers can work at 1,500/3,000 revolutions per minute.

Depending on how fine the milled paste is to be, the outer sieve can be changed so that what passes through it can be larger or smaller.

The conveyor belt carries the olives to the lower part of the drum where the first hammer circle begins the grinding process.

When the fragments reach a specific size, the same centrifugal force moves them to the upper part of the drum through the first sieve (with holes of 10mm in diameter). Here, the second circle of hammers continues to grind the paste.