Agriculture Reference
In-Depth Information
temperature), enzymatic lipolysis (endogenous to the
fruit), microbial lipolysis (as a result of microflora in the
fruit), and oxidation of the oil (due to peroxide formation
in the unsaturated fatty acids) (Alba, 2008). In these
situations, it is best to store the fruit in a cool, ventilated
area that is protected from the outside.
Solid-liquid separation
The intent of this procedure is to separate the liquid in the
paste (oil and waste water) from the solid (skin, pulp, and
broken pits), known as “olive pomace.” There are three
types of systems: selective filtration, pressure extraction,
and centrifugation.
Cold selective filtration produces high-quality oil; how-
ever, it is rarely used due to its high cost (Hermoso et al.,
1991).
The hydraulic press is the traditional system employed.
It places the paste on filters made of esparto or synthetic
fiber. This is all located on a trolley with a central spike and
all under a press that when activated drives the oil out of
the capacho (press mat), toward the trolley. This system is
used in only 3% of the Spanish oil mills, whereas in Italy,
46% of the industries use this method (Alba, 2008).
The use of a centrifuge represents the modernization of
the olive oil industry. The mixed paste is introduced (par-
tially diluted in water) into a horizontal centrifuge called
a decanter. The rotation (around 3500 rpm) separates the
solid material from the liquid phase, thereby forming three
phases: a solid olive pomace, or orujo, and two liquids
(oil and residual vegetable water). This system is known
as three-phase centrifugation. This system is used in 43%
of oil mills in Italy, whereas in Spain, it represents only
10% (Alba, 2008). Although this system has many ad-
vantages, it has a number of disadvantages, including a
large volume of aqueous waste (residual vegetable water)
of approximately 0.7-1.1 liter/kg of olives. This effluent
contains a high quantity of contaminants, as evidenced by
the fact that chemical demand for oxygen and spillage into
public waterways negatively affects flora and fauna (Alba,
2008). A variant of this system has been developed called a
two-phase centrifugation system that does not need to thin
the paste with the addition of extra water. As is apparent
from its name, this system produces only two residues: a
two-phase solid olive pomace, or alpeorujo (which incor-
porates the vegetable water and is therefore more humid),
and another liquid (in this case, oil) (Hermoso et al., 1995).
The final effluent in this production system is reduced to
0.25 liter/kg of olives. This process is the most predominant
system used in Spain (87%), although the distribution of
this system depends on the country. Italy, for example, uses
it in only 11% of its olive oil industries (Alba, 2008).
Cleaning and washing
These operations are necessary to avoid contamination,
which in turn prevent damage to the machinery. Leaves
are removed, by vacuum cleaner or fan, since they signif-
icantly alter the sensory characteristics of virgin olive oil
(green leaf taste).
Milling
This stage consists of pressing the fruit with a mill to re-
lease the occluded oil in the mesocarp cells. There are two
large groups of mills: stone types (with conical or cylindri-
cal rollers) and the more current metal types, which include
hammer, toothed disk, or grooved cylinders. The choice de-
pends on the mill, although the overall objective is to reduce
surface area and milling time and limit the incorporation of
trace metals (Civantos, 2008c). The key variables to con-
sider during the process of milling are uniformity (to obtain
maximum efficiency in the mixing), degree of milling (av-
erage size of the hardest particles in the paste), speed (if
excessive, it can cause heating), aeration, and impurities
(which should be limited as much as possible).
Mixing
The purpose of this phase is to collect all the oil droplets
and break the oil-water emulsion. Mixing is carried out
with stainless steel beaters with vertical or horizontal ro-
tors (20-40 rpm) with rotating arms that are most com-
monly used these days. During the mixing process, various
aspects need to be regulated such as the speed of the pad-
dles (if excessive, emulsions may form), mixing time (since
this affects polyphenol content), and the temperature of the
paste (Civantos, 2008c). As a guideline, the paste may be
heated by hot water circulation between 22 and 25 Cfor
20-30 min (Di Giovacchino, 2003). During milling and
mixing, the paste organizes itself into a reticular structure
whose spaces retain oil and “alpechin” (olive mill wastew-
ater). Difficult pastes are those in which oil extraction is
hampered by a total or partial loss of this structure. In these
cases, one can use technological additives. The legally au-
thorized additives are those without chemical or biochemi-
cal action such as natural micro-talc (hydrated magnesium
silicate). Their use facilitates the absorption of oil droplets
and increases extraction between 1% and 3%.
Liquid-liquid separation
The oil must be purged of certain impurities such as wastew-
ater and some solids. The separation of solids can be per-
formed by using vibratory sieves of filters, while separation
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