The Technique of olive oil extraction
The extraction of extra virgin olive oil from freshly harvested olives is a very delicate process and critical to the quality of the product. The process is divided into four phases: crushing, churning, pressing and separating the oil from water. What follows is a brief description of these phases to explain the high quality of olive oil from Foa.
The first phase is the frangitura, the crushing of the olives( from which the name frantolio, olive press comes,) in the course of which the pulp and the kernels of olives are split and crushed, obtaining a thick olive paste. The traditional pressing techniques used grinders typically of granite, of cylindrical shape on a base also of granite, thereby crushing with their weight the olives. This type of pressing, although fascinating in terms of the history and tradition of olive oil, has the disadvantage of requiring longer processing times and thus results in a prolonged exposure to air that begins the oxidation process sooner. The modern techniques of pressing (the results of some amazing Italian innovations) use hammers or rotary discs that have the ability to crush the olives quickly , minimizing the length of exposure of the mixture to the air and which produces a more uniform particle size of the solid part ( core ) than that obtained with the grinders . This system is now preferred as it is easier to clean than the old millstones and thus is more hygienic. The risk of modern presses is that if the operation is not followed scrupulously, the process can be too fast, causing a rise in temperature of the mixture that significantly alters the organoleptic characteristics of the product.
The olive paste is then subjected to gramalatura, in English, maxalation, which consists of a continuous and prolonged churning which unifies the oil droplets in always larger drops that in the next phase can be more easily separated from the solid part. This is essential with the use of the mechanical presses that promote the coalescence of the droplets of oil trapped in the solid part of the paste. At this stage it is vital the process of mixing takes place at temperatures below 28 ° C, higher temperatures may give yields of 10-20 per cent extra oil, but at the expense of the quality of the components, as the “noble" nutrients are particularly temperature sensitive. [ Some churning processes limit contact with air by operating in an environment saturated with nitrogen : this feature allows you to retard the oxidation processes and at the same time restoring the outstanding primary aromas].
The extraction phase itself, called pressing, leading to the separation of the three components of the paste : extra virgin olive oil, water and solid matter. There are several methods of pressing based on two types of process: continuous or discontinuous .
Discontinuous is the most traditional system in which the extraction takes place by mechanical pressure. The olive paste is spread on discs of vegetable fiber or coconut fiber called fiscoli (which nowadays are made of synthetic materials ) : fiscoli are stacked in cylinders and interspersed with steel disks to equalize pressure that is applied gradually. The pressure squeezes the liquid oily component from the vegetation . The traditional system is very charming and can provide excellent oils , but strainers are difficult to clean and can absorb and transmit tastes and odours of the already strained olives, so have a high risk to subsequent pressings of serious defects in the earlier ones, such as the olive fruit fly or mold .
The solid residue that at the end of the pressing remains stuck to the fiscoli still contains 5-8 % oil, which subsequently may be separated with the use of chemical solvents in similar procedures to those used for seed oils . The remaining olive pomace is an excellent bio fuel .
In the continuous method , the more modern, mechanical pressure has been replaced by other physical processes that lead to the separation of the liquid portion from the solid: the most common is a centrifugal system that decants the oil by exploiting the different specific weights of the three individual components. The dough is first fluidized by the addition of water to a temperature equal to that of the paste.
In the last phase there is the separation of the oil from the vegetable matter which is facilitated by using the difference of the weight of the oil compared with that of water. At the end of this operation the oil is cloudy and opaque. It is already edible as it releases its intense aromas. In the weeks immediately following foreign substances are deposited on the bottom of the container leaving small traces of impurities: such as water particles, waxes, vegetable residues that the separator failed to separate from the oil. These can then be easily discarded.