**3.7. Olive oil storage**

166 Olive Germplasm – The Olive Cultivation, Table Olive and Olive Oil Industry in Italy

Servili et al., 1999d; Stefanoudakii et al., 1999; Di Giovacchino et al., 2001).

and their subsequent use for residual oil recovery by solvent extraction.

procedures which comply with the regulations of the law.

**3.6. Separation of the oil from vegetation water** 

Finally, the impurities are collected even further away.

the olive oil storage tanks.

quality oils and machines featuring high yields to be obtained (Ranalli & Angerosa, 1996;

As regards the by-products obtained by centrifugation, it is important to recall here that, whereas the aforementioned problem concerning the use of three-phases traditional systems is represented by the enormous amounts of vegetation water to be drained (0.7-1.2 m3/ton), the main problem, when using the two-phases systems, is not only a decrease in oil quality, but also the high humidity level of the pomaces (50% for the traditional three-phases decanters, 55-60% for the two-phases). This last aspect implies two disadvantages: i) where to store by-products of the extraction process; ii) how to transport to the pomace oil factory

The pomaces produced by two-phases system are generally employed for the production of compost or for spreading to improve agriculture soil, following a process similar to that used for the vegetation water of olives. In this context, three-phases decanters with low water consumption can represent an adequate alternative with respect to the two-phases extraction system, because they allow a quality of oil to be obtained which is comparable to that of oils obtained using the two-phases system, and pomaces with a reduced humidity content, similar to those produced by the traditional three-phases systems. On the contrary, they produce a certain amount of vegetation waters, which imply water draining

The liquid coming from the extraction system is called "oily must", and consists of oil and vegetation water, which is separated by using vertical centrifuges. The oily must also contains solid particles and mucilage (0.5 to 1.0%). These substances are suspended if they are very small, whereas they are easily separated from the liquid if they are of an appreciable size (seed fragments and/or epicarp of olive fruit fragments). In particular, separation from the liquid is carried out by using a sieve (1~2 mm mesh) placed at the top of

Disk stack centrifuges, suitable for separating solid impurities with a specific weight ranging from 1.050 to 1.150, are used to separate the oil from the oily must. The basic principles of centrifugation are well known. If a vigorous rotational motion is applied to the oily must (oil, vegetation water and impurities), the lighter part (i.e. the oil) is collected close to the axis of rotation, while the heavier part (i.e. the water) is collected further away.

Moreover, spillways enable the oil as well as the vegetation waters and impurities to be recovered. A fraction of the impurities is deposited on the rotating drum, which must be periodically cleaned, even though self-cleaning decanters are widely used. In fact, these decanters work in a continuous cycle, providing a periodical and automatic discharge of the sediment, which could compromise the centrifugation process. The decanters most During storage, the phenolic composition of EVOO is modified by the endogenous enzymatic activities contained in the cloudy phase. These enzymes may reduce the "pungent" and "bitter" sensory notes, the intensity of which is strictly linked to the content of aglycon secoiridoids, and, at the same time, can produce olfactory and taste defects. Oil filtration partially removes the water and enzymes from EVOOs, and enables the EVOO phenolic content to stabilize during its storage. The filtration process of EVOO is a procedure carried out in two steps: first, the suspended solids are removed, and second, the elimination of humidity gives the oil a brilliant aspect. Normally, organic or inorganic materials are used in conjunction with a variety of filtration equipment to enhance or enable the separation of suspended solids and water-oil. The type of such equipment, often called filter aids, depends on the final objective (Montedoro et al., 2005).

The olive oil profile changes during its storage, due to the simultaneous, drastic reduction in compounds from the LOX pathway and to the neo-formation of volatile compounds, responsible for some common defects referred to as "rancid", "cucumber" and "muddy sediment" (Morales & Aparicio, 1997; Angerosa et al., 2004; Servili et al,. 2009a).

This runs parallel to the increase in saturated aldehydes nonanal, and above all hexanal in the oxidation process, but it cannot be considered a useful marker of oxidation, since it is also present in the aroma of high quality EVOOs (Angerosa et al., 2004; Servili et al., 2009a).

Furthermore, the presence of sediment as a result of the decantation of unfiltered olive oil during its storage can determine, under suitable temperature conditions, the production of unpleasant compounds responsible for the typical "muddy sediment" defect due to the fermentation which produces compounds, probably of the butyric type (Angerosa et al., 2004; Servili et al., 2009a).
