The EVOO grinding and extraction process

The Milling Process

Milling is the term used for the process of grinding or crushing olives to extract their oil. Generally, it involves breaking the pulp cells of the olives and extracting their juice, i.e., the oil.

At the beginning of the harvest, when the olives are still green, the oil-containing cells are smaller, which means the crushing needs to be much finer and more delicate. Once the olives ripen and their cells become larger, the crushing can be coarser.

Innovation and technological development have allowed for the implementation of a modern technological system using a hammer mill and a "centrifugation" process, which we will discuss later. Both accelerate the process while ensuring proper hygiene to achieve an optimal result.

After harvesting, the olives are cleaned of impurities and any remaining stones or twigs are removed. Now begins the first step, called "milling." This is done using hammer mills. In this step, the olives are crushed in the mill, breaking their structure. The resulting paste then goes to kneaders where rotating blades work for about 20 minutes. This homogenizes the paste and combines the oil molecules. This kneader is water-controlled and also maintains control over temperature and oil extraction.

During the process, temperature influences the quality of the EVOO. At lower temperatures, the EVOO will have higher quality, as it better preserves the organoleptic properties of the olive. Unfortunately, this does reduce the quantity obtained, as it will be less compared to making oil at higher temperatures. By reducing the temperature to less than 27ºC, cold-extracted EVOO is achieved.

Centrifugation

Once the kneading phase is complete, the centrifugation process begins. This system originally consisted of three phases, but thanks to technological advances, the industry has now reduced this centrifugation process to two. Therefore, what was previously divided into three phases (solid phase, liquid oil, and liquid pomace water) is now reduced to two centrifugation phases. Furthermore, this system has been shown to be more efficient and is therefore the most widely used in Spanish olive mills.

Thus, a horizontal centrifuge is used to separate the liquid part, i.e., the oil, from the solid part, which includes the olive skin, pit, water, and some oil. This solid phase is known as "alpeorujo," which is de-pitted at the factory itself. Afterward, it goes to pomace extractors.

The obtained liquid phase is then subjected to further centrifugation. This second centrifugation is vertical and will separate the oil from the water.

The last part of the process would be filtration. Filtering improves the quality of the oil and extends its optimal condition. This way, we remove moisture and impurities from the oil that cause the product to oxidize more quickly. Thus, the oil will be preserved in better condition.

Finally, the oil is stored in tanks protected from sudden temperature changes. Storage in air-conditioned cellars will also protect it from light while awaiting bottling.

Now you have a clearer understanding of how the milling and extraction processes work in the production of EVOO at Aceites Ad Morum. All that's left is to try our product— the store is just one click away!