sensory characteristics. The major olive oil production is localised in the Mediterranean area. The European Union (EU) is the first producer with almost 2.5 million
tons in 2013–2014. From the non-European countries, Tunisia, Syria, Turkey and
Morocco are the other important producing countries, whereas a great year-by-year
variability is observed because of the olive plant physiology. The EU accounts for
80–90% of the world olive production. Spain, Italy and Greece specifically produce
45%, 25% and 20% of the world olive oil production, respectively (IOC 2015a).
Olive oil is contained mostly as vacuoles inside the mesocarp cells of the fruit,
and very little amounts are found in the seed. The extraction herein reported is
referred to as “virgin olive oil” (VOO), whose name comes from the fact that no
chemical solvent or other chemical means is allowed for its extraction. Thus, by
definition, VOO is obtained by only physical treatment of the olive fruits. The first
processing step implies crushing of the olives, using a metallic “hammer”-based
system (or other crushers) or a more traditional mill stone, to give the so-called olive
paste. This is a mixture of solids, water contained in the drupe and the oil. The solids
are removed by either pressing the olive paste using traditional hydraulic press
systems or by more modern horizontal centrifuges that separate the different fractions according to their density. Two main centrifuge systems exist, i.e. “threephase” or “two-phase”, which are improperly named after the number of products
obtained, i.e. water, oil and solids in the first case and oil and wet slurry named
alperujo in the second case. A second centrifugation is often carried out to remove
residual water in the oil. The final product is a turbid opalescent liquid that is finally
clarified by deposition in the tanks or filtration. Unfiltered—veiled—virgin olive oil
is generally richer in phenolic compounds, and it is popular among some consumers
and chefs who judge the opalescent appearance as an indicator of higher wholesomeness and flavour. However, the unfiltered oil can undergo fermentative processes with consequent appearance of some sensory defects. Presently, large-scale
production of cloudy oil is prevented because it has a limited stability due to
sedimentation of the solid residues and water, with consequent quality deterioration
and appearance of sensory defects (Tsimidou et al. 2005; Zullo and Ciafardini 2017).
A crucial step between olive crushing and the solid-liquid separation is
“malaxation”. This process is specific for virgin olive oil production and consists
of a slow mixing of the olive paste at relatively high temperature (possibly not
exceeding 28
C to avoid excessive oxidation). This process is aimed to promote
coalescence of fat droplets so that a higher extraction yield is obtained in the
subsequent centrifugation. It has also a crucial importance in terms of phenolic
and flavour compound formation, as most of the lipid oxidation reactions take
place during malaxation, with formation of aroma compounds and dramatic change
of phenolic compound composition. The influence of each of these steps on EVOO
flavour is reported in the following paragraphs.
Detailed description of the different equipment available for olive oil extraction is
reported in a book recently published by Peri (2014), which covers all aspects related
to processing condition and olive mill equipment. The reader can also refer to
Clodoveo et al. (2015) for information about the production steps in relation to
minor bioactive constituents and new strategies to develop continuous plants.
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213
tons in 2013–2014. From the non-European countries, Tunisia, Syria, Turkey and
Morocco are the other important producing countries, whereas a great year-by-year
variability is observed because of the olive plant physiology. The EU accounts for
80–90% of the world olive production. Spain, Italy and Greece specifically produce
45%, 25% and 20% of the world olive oil production, respectively (IOC 2015a).
Olive oil is contained mostly as vacuoles inside the mesocarp cells of the fruit,
and very little amounts are found in the seed. The extraction herein reported is
referred to as “virgin olive oil” (VOO), whose name comes from the fact that no
chemical solvent or other chemical means is allowed for its extraction. Thus, by
definition, VOO is obtained by only physical treatment of the olive fruits. The first
processing step implies crushing of the olives, using a metallic “hammer”-based
system (or other crushers) or a more traditional mill stone, to give the so-called olive
paste. This is a mixture of solids, water contained in the drupe and the oil. The solids
are removed by either pressing the olive paste using traditional hydraulic press
systems or by more modern horizontal centrifuges that separate the different fractions according to their density. Two main centrifuge systems exist, i.e. “threephase” or “two-phase”, which are improperly named after the number of products
obtained, i.e. water, oil and solids in the first case and oil and wet slurry named
alperujo in the second case. A second centrifugation is often carried out to remove
residual water in the oil. The final product is a turbid opalescent liquid that is finally
clarified by deposition in the tanks or filtration. Unfiltered—veiled—virgin olive oil
is generally richer in phenolic compounds, and it is popular among some consumers
and chefs who judge the opalescent appearance as an indicator of higher wholesomeness and flavour. However, the unfiltered oil can undergo fermentative processes with consequent appearance of some sensory defects. Presently, large-scale
production of cloudy oil is prevented because it has a limited stability due to
sedimentation of the solid residues and water, with consequent quality deterioration
and appearance of sensory defects (Tsimidou et al. 2005; Zullo and Ciafardini 2017).
A crucial step between olive crushing and the solid-liquid separation is
“malaxation”. This process is specific for virgin olive oil production and consists
of a slow mixing of the olive paste at relatively high temperature (possibly not
exceeding 28
C to avoid excessive oxidation). This process is aimed to promote
coalescence of fat droplets so that a higher extraction yield is obtained in the
subsequent centrifugation. It has also a crucial importance in terms of phenolic
and flavour compound formation, as most of the lipid oxidation reactions take
place during malaxation, with formation of aroma compounds and dramatic change
of phenolic compound composition. The influence of each of these steps on EVOO
flavour is reported in the following paragraphs.
Detailed description of the different equipment available for olive oil extraction is
reported in a book recently published by Peri (2014), which covers all aspects related
to processing condition and olive mill equipment. The reader can also refer to
Clodoveo et al. (2015) for information about the production steps in relation to
minor bioactive constituents and new strategies to develop continuous plants.
9 Olive (Olea europaea)
213