**3. Processing and elaboration of olives and olive oil**

In this section, the steps required for obtaining high-quality olive oil (extra virgin) and table olives will be described. It is important to know the details of the processing in order to understand in which step can the contamination by herbicides take place.

#### **3.1 Olive oil**

### **3.1.1 Harvest of olives**

The harvest of the olives could be understood as an independent activity from the elaboration of the oil. However, the characteristics of the oil are highly influenced by the harvest time and method employed.

Olives must be picked at the moment of optimum ripeness, where the fruit presents the maximum content of oil and the best characteristics. Olives reach their ripeness in autumn and picking starts at the end of November, lasting up to February or March. The methods to harvest the olives have not changed much from the ancient time. The methods used should not damage the fruit and should avoid breaking of boughs or shoots. The high-quality olive oil is obtained by "milking" the olives into a sack tied around the harvester's waist (using ladders for the highest boughs) and extending canvases at the foot of the trees, where the olives will fall when the tree is beaten (using flexible poles). Recent methods make use of harvester machines (shakers) that generate the vibration on the tree for the falling of the fruit. This vibration machines can be small vibrators operated by the farmer in the required boughs, of full-equipped tractors, with vibration units for the whole trunk of the tree and an umbrella to pick the olives.

Harvest by hand is impossible in olive trees of 4-5 meters high, even with the use of ladders. In general, the trunks are to wide to allow the use of vibration machines and the olives are picked directly from the ground after they fall down when they reach ripeness. Hence, harvest period lasts longer, even until spring when it is a high-production year. When the olives are picked from the ground, weeds have to be completely eliminated from the zone in order to make it easier the picking. The quality of the olive oil obtained from this olives is poor due to organoleptics flaws such as soil flavor.

#### **3.1.2 Washing**

Traditionally, agricultural workers have cleaned the fruit in the fields by means of sieves. But this cleaning is not complete and the fruit goes into the olive-oil mill with a great quantity of impurities, leaves, branches, mud, etc, which are necessary to eliminate. Therefore, for this purpose, cleaners that use air current or shaking sieves are used to eliminate leaves, branches and other impurities lighter than the fruits. In addition, washing devices are employed to eliminate heavier impurities such as stones or dust. In next figures, both cleaning steps, the one with the air for light impurities (Figure 1) and the other one by washing for heavy impurities (Figure 2), are shown.

Once the fruit has been cleaned and weighed, it is stored in hoppers until it can be crushed. The storage period must be as short as possible in order to avoid alterations, which will produce oils with a higher degree of acidity, lower stability and worse flavor.

Washing device

Fig. 1. Cleaning steps for olive fruit.

210 Herbicides – Properties, Synthesis and Control of Weeds

In this section, the steps required for obtaining high-quality olive oil (extra virgin) and table olives will be described. It is important to know the details of the processing in order to

The harvest of the olives could be understood as an independent activity from the elaboration of the oil. However, the characteristics of the oil are highly influenced by the

Olives must be picked at the moment of optimum ripeness, where the fruit presents the maximum content of oil and the best characteristics. Olives reach their ripeness in autumn and picking starts at the end of November, lasting up to February or March. The methods to harvest the olives have not changed much from the ancient time. The methods used should not damage the fruit and should avoid breaking of boughs or shoots. The high-quality olive oil is obtained by "milking" the olives into a sack tied around the harvester's waist (using ladders for the highest boughs) and extending canvases at the foot of the trees, where the olives will fall when the tree is beaten (using flexible poles). Recent methods make use of harvester machines (shakers) that generate the vibration on the tree for the falling of the fruit. This vibration machines can be small vibrators operated by the farmer in the required boughs, of full-equipped tractors, with vibration units for the whole trunk of the tree and an

Harvest by hand is impossible in olive trees of 4-5 meters high, even with the use of ladders. In general, the trunks are to wide to allow the use of vibration machines and the olives are picked directly from the ground after they fall down when they reach ripeness. Hence, harvest period lasts longer, even until spring when it is a high-production year. When the olives are picked from the ground, weeds have to be completely eliminated from the zone in order to make it easier the picking. The quality of the olive oil obtained from this olives is

Traditionally, agricultural workers have cleaned the fruit in the fields by means of sieves. But this cleaning is not complete and the fruit goes into the olive-oil mill with a great quantity of impurities, leaves, branches, mud, etc, which are necessary to eliminate. Therefore, for this purpose, cleaners that use air current or shaking sieves are used to eliminate leaves, branches and other impurities lighter than the fruits. In addition, washing devices are employed to eliminate heavier impurities such as stones or dust. In next figures, both cleaning steps, the one with the air for light impurities (Figure 1) and the other one by

Once the fruit has been cleaned and weighed, it is stored in hoppers until it can be crushed. The storage period must be as short as possible in order to avoid alterations, which will

produce oils with a higher degree of acidity, lower stability and worse flavor.

**3. Processing and elaboration of olives and olive oil** 

**3.1 Olive oil** 

**3.1.1 Harvest of olives** 

umbrella to pick the olives.

**3.1.2 Washing** 

poor due to organoleptics flaws such as soil flavor.

washing for heavy impurities (Figure 2), are shown.

harvest time and method employed.

understand in which step can the contamination by herbicides take place.

Fig. 2. Washing step for olive fruit.

#### **3.1.3 Preparation**

The process of releasing the oil from the plant tissue begins by milling the olives to tear the flesh cells in order to let the oil run out of the vacuoles. This is followed by stirring the olive paste to permit the formation of large drops of oil and to break up the oil–water emulsion. In so-called "dual-phase decanters" the oil is then separated by direct continuous centrifugation from the pomace, which consists of vegetable matter and water. The yield of oil varies from 80 to 90% of the total oil content of the olives, because the oil in the olive paste is only partially free to escape and part of it remains in the unbroken cells or is trapped in the tissues of the cytoplasm, or is emulsified in the aqueous phase.

After the extraction of virgin olive oil from the olives, the remaining paste is called pomace and still contains a small quantity (2-6%) of oil that can only be extracted with chemical solvents. This is done in specialized chemical plants, not in the oil mills and the obtained oil is called pomace oil.

Evaluation of the Contamination by Herbicides in Olive Groves 213



Other trade preparations include dehydrated and/or shrivelling olives and specialities

The denomination pesticides (or plaguicides) include a wide variety of products that are very different in their chemical composition and characteristics. A plaguicide can be described as a substance (or formulation containing at least one of them) that presents any

Fight agents that can be harmful for the crops or prevent the potential effects of these

Destruct or prevent the action of potentially harmful organisms different to the ones

Taking into account the specific action of the plaguicides, different classifications can be

 Insecticides are used against insects and they include ovicides and larvicides (against eggs and larvae of insects, respectively). Nearly all insecticides have the potential to

Fungicides are chemical compounds or biological organisms used to kill or inhibit fungi

 Nematocides, disinfectants and fumigants in general, used to kill parasitic nematodes. Herbicides are used to kill unwanted plants while leaving the desired crop relatively

 Phytoregulators and similar products can be used to improve the potential of the trees. Molusquicides and rodenticides are used to control molluscs (slugs and snails) and

Laboratory studies show that pesticides can cause health problems, such as birth defects, nerve damage, cancer, and other effects that might occur over a long period of time. However, these effects depend on how toxic the pesticide is and how much of it is

common preparation is "natural black olives".

**4. Pesticides: definition and classification** 

 Control or regulate the vegetable production. Protect the vegetable production, including woods.

Destruct part of the vegetables or prevent undesirable growths.

made, being the decimal classification one of the most frequently used:

significantly alter ecosystems, being many of them toxic to humans. Acaricides kill members of the Acari group, which includes ticks and mites.

as "black olives".

prepared in different forms.

of the following uses:

Destruct weeds.

that attack plants.

or fungal spores.

unharmed.

rodents pests.

Post-harvest pesticides and seeds.

Other specific plaguicides.

Protectors of woods, fibers and derivatives.

agents.

The FFA limit in olive oil for direct consumption is 2%. Virgin olive oils with higher content are called "lampantes" and must be refined prior to consumption. The components to be removed are all those ones that are detrimental to the flavor, color and stability of the oil, mainly FFA, phosphoacylglycerols, pigments, volatiles and contaminants. The standard processes used are chemical and physical refining. The main difference between both processes is that chemical refining procedure includes caustic soda treatment to neutralize the oil while, following physical refining, FFA are eliminated by distillation during deodorization. Physical refining reduces the loss of neutral oil, minimizes pollution and enables recovery of high quality FFA. Nevertheless, not all oils can be physically refined.

#### **3.2 Table olives**

 "Table olives" means the product: a) prepared from the sound fruit of varieties of the cultivated olive tree (*Olea europaea L*.) that are chosen for their production of olives whose volume, shape, flesh-to-stone ratio, fine flesh taste, firmness and ease of detachment from the stone make them particularly suitable for processing; b) treated to remove its bitterness and preserved by natural fermentation or by heat treatment, with or without the addition of preservatives; c) packed with or without covering liquid (International Olive Oil Council, 2004).

Table olives are classified in one of the following types according to the degree of ripeness of the fresh fruits:


To prevent olive damage, fruits destined for table olives production are picked by hand and carefully placed in special padded basket that are hung by their neck. Olive transportation is carried out in perforated plastic containers, which have plastic netting as walls (supported by an iron structure). The perforated walls permit the aeration of the fruits and the reduced weight also contributes to minimizing the damage of the fruits. Sometimes, olives are also transported in bulk, although this transportation system is not recommended due to the increased risk of damaging the olives.

Once the olives have been transported, their processing takes place. In general, any processing method aims to remove the natural bitterness of the fruit, caused by the glucoside oleuropein. The bitterness may be removed by alkaline treatment, by immersion in a liquid to dilute the bitter compound, or by biological processes. The product so obtained may be preserved in brine according to its specific characteristics, in dry salt, in a modified atmosphere, by heat treatment, my preservatives, or by acidifying agents. The most common trade preparations are (Sánchez et al., 2006):



Other trade preparations include dehydrated and/or shrivelling olives and specialities prepared in different forms.
